Normally I limit my investigations of stem-feeding insects to those that produce some kind of external evidence that catches my eye (a certain wingstem stem being an exception), but last spring , for whatever reason, I decided to have a peek inside a dead stem of tall blue lettuce (Asteraceae: Lactuca biennis) that had been leaning against the side of my house, right by the front door, all winter long. On April 12, I broke off a short chunk from the top of the stem, split it lengthwise, and immediately saw that there were little round cells in the walls of the stem with larvae inside.
I guessed these must be cryptic wasp galls—something I’d first become aware of in 2019 when two adults of Aulacidea harringtoni (Cynipidae) emerged from a two-inch piece of a Lactuca canadensis stem I’d collected the previous July because it had a puparium of a stem-mining agromyzid fly on the surface.
I put the split pieces of the L. biennis stem in a jar, along with a couple of intact pieces from farther down the stem, and put the jar on a shelf in my office to find out if my guess was right.
Between May 9 and June 10, ten of these wasps emerged in the jar:
These are eurytomid wasps (Eurytoma sp.), which are parasitoids of gall insects rather than being gall inducers themselves. When the first ones emerged, I figured this would be a good time to see some wasp pupae, so I split one of the intact stem pieces. The exposed cells still had larvae inside, and there was also a spider living in the stem’s hollow center.
I think this spider is in the genus Euryopis (Theridiidae), which makes distinctive tufted egg sacs—one of which (maybe) is shown in this post. Here’s a closer view of the above wasp larva:
On May 27, this beetle appeared in the jar.
This is Isohydnocera curtipennis (Cleridae), which I had seen a couple of times in June 2020 wandering around on milkweed plants in my yard. Until this one appeared in that jar, I had been completely unaware that these beetles develop in galls of other insects. It turns out this same species has been reared from stem galls of the goldenrod gall moth Gnorimoschema gallaesolidaginis (Gelechiidae), and of Euura salicisnodus (Tenthredinidae), a sawfly that causes galls in willow stems*.
Between May 29 and June 27, 22 gall wasp adults emerged. Louis Nastasi tells me they belong to an undescribed species of Aulacidea.
I did eventually see a gall wasp pupa, on June 10. I think it was from one of the larvae whose cells I had broken open, and was found loose on the bottom of the jar.
Meanwhile, another 24 parasitoid wasps emerged between June 18 and 27. Twenty-two of them were pteromalids; I’m not sure if the ones shown below are two different species or differently colored male and female of the same species. Probably I’ll never know; I’ve never been able to get anyone to identify the pteromalids I’ve reared over the years.
And there were two of these ormyrids (Ormyrus sp.).
I got the feeling that more and more wasps would just keep emerging indefinitely, but I had to leave for a six-week road trip at the beginning of July, so that’s where the story ends. If you want to learn more about these herb gall wasps—and maybe help make some new discoveries—take a look at Louis Nastasi’s post here. (Most of the galls, by the way, are externally obvious, not cryptic like the ones in this lettuce stem.)
[Edit, 3/20/2024: Louis saw this post and he assures me that all of these parasitoid wasps are undescribed, not just the Aulacidea, for which he already has a name picked out, and he thinks the pteromalids may belong to the genus Homoporus.]
* Sabrosky, Curtis W. 1934. Notes on the larva and larval habit of Isohydnocera curtipennis (Newmn.) (Coleoptera, Cleridae). Journal of the Kansas Entomological Society 7(2): 65-68.
Uh-oh, spring has arrived—as evidenced by the hazelnuts starting to bloom in my yard—and I haven’t finished going through last year’s photos yet. I have, however, made it far enough to finish this post I started a few months ago. The story starts in August 2020 when, as you may recall, I was keeping a running list of all the leafminers I found in my yard. The 23rd installment of that series included this entry toward the bottom:
“I don’t remember specifically planting garden phlox (Polemoniaceae: Phlox paniculata), but it’s been jumping around our yard for a few years now.
“I’ve been watching it closely for leaf mines of Liriomyza phloxiphaga (Agromyzidae), which is known from a single specimen I reared from phlox in my mother’s garden three years ago. No luck so far, but on August 17 I did find this:
“Leafminer #153: A heretofore unknown leafminer that forms a narrow linear mine in leaves of garden phlox, soon entering the midrib and presumably continuing into the stem—as with Marmara viburnella, but this isn’t a Marmara; at this point I’m not sure what insect order it belongs to. I can’t see an eggshell at the beginning of the mine, there is no evident frass or larva when I backlight the leaf, and there is no external evidence of feeding in the stem.
“I’ve found one other example so far, right next to the garage.”
In the 30th installment (two months later), I included this update:
“On October 11, I finally collected the mysterious Leafminer #153, which forms a short mine in a leaf blade of garden phlox before disappearing into the midrib and, I surmised, completing its development as a stem borer without leaving any further external evidence.
“I split open a couple of stems that had mines like this, and sure enough, something had been tunneling in the pith:
“Since the mine isn’t really visible in the leaf midrib and since the midrib and stem are difficult to dissect cleanly, I wasn’t able to see the mine actually transitioning from the leaf to the pith of the stem, but I confirmed that there was no tunneling in the stem immediately above a mined leaf but there was a tunnel right at the node with the mined leaf. I didn’t want to break apart too many stems for fear of damaging the larvae or pupae that I hope are still inside, but it seems that the tunneling continues all the way to the ground. Hopefully I got enough of the root to capture the mystery bug, and will be able to see who comes out in the spring.”
Nothing ever emerged from that stem, but in the spring I watched the phlox plants closely, and on May 27 I noticed the mines had appeared:
This example shows something that was also evident in the one I had found by the garage in October: associated with the mine are a bunch of little dots, which are “host-feeding” punctures a female agromyzid fly makes with her ovipositor, not for the purpose of laying eggs but to drink the juices that bubble out of the wounds—for nutrition and, I imagine, to “taste” and confirm that it is a suitable leaf to lay eggs in.
Not only did I see this strong circumstantial evidence that an agromyzid was responsible, I actually got to see several females making these punctures on the same day.
A shiny, metallic agromyzid fly whose larva lives as a stem borer is likely to belong to the genus Melanagromyza, which I don’t know much about because none of them are supposed to be leafminers. I collected one and sent it to Owen Lonsdale, even though I was pretty sure all he would be able to say was yup, that’s a female Melanagromyza, and we need to see male genitalia to get it to species—which is exactly what happened.
In July 2021, I uprooted a few mined phlox plants and put them in a clear garbage bag, but the only fly that ever appeared in it (in early September) was this “little house fly,” Fannia canicularis (Fanniidae):
In May of 2022, I split open a couple of the previous year’s phlox stems and found an empty Melanagromyza puparium in one of them—so the larvae evidently don’t always make it into the roots.
Nevertheless, most of the tunnels in the stems I split did go all the way to the ground. So that fall, I marked several plants that had leaf mines on them, and last April I dug two up, bagged them, and put them in the corner of my office to keep an eye on. (This, and what happens next, may look familiar if you’ve been following this blog for a while.)
Over the next several weeks, the tiny creatures that appeared in the bags included this 8-mm jumping spider (Salticidae: Phidippus princeps)…
…lots of dark-winged fungus gnats (Sciaridae; this one was <2 mm long)…
…this 5.5-mm soldier fly (Stratiomyidae), which is Allognosta fuscitarsis, the same species I once reared from a larva that had apparently arrived on the kitchen counter by way of a zucchini from the garden…
…and at last, a 2-mm male Melanagromyza! Somehow I sensed that this would be the only one, and I was worried I would lose it if I tried to get a live photo, so I chickened out and put it in the freezer first.
This winter, Owen and I have been working on a paper that deals with all the specimens I sent him through 2022, saving the 2023 specimens for a future paper. But since we were already describing a new Melanagromyza species John van der Linden had reared from a different phlox species in Iowa, it made sense for him to have a look at this specimen too. His assessment: another new species! I’ll reveal its name once that paper is published.
But wait, there were still more things appearing in those bags, like this ~2.5-mm “dusky lady beetle” (Coccinellidae, tribe Scymnini)…
…this ~1.3-mm spider, which I think is an Agroeca (Liocranidae)…
…this ~1.7 mm beetle (another Stilbus)…
…several ~1-mm spiders I can’t identify, and for which no one on BugGuide has suggested IDs yet…
…this ~1.2 mm “pleasing fungus beetle” (Erotylidae: Toramus pulchellus)…
…this ~1.5 mm “dirt-colored seed bug” (Rhyparochromidae: Antillocoris)…
…more and more dark-winged fungus gnats, which are consistently difficult to photograph alive, but I managed with this 3-mm long one…
…a bunch of little blackish slugs (Agriolimacidae: Deroceras)…
…this 4-mm casebearer moth larva (Coleophoridae), probably a species in the goldenrod-feeding Coleophora duplicis complex…
…this 5-mm wolf spider (Lycosidae)…
…this 5.5 mm ichneumonid wasp (tribe Phaeogenini; larvae are internal parasitoids of caterpillars)…
…this 2.4 mm eulophid (tribe Entedonini; similar to some of the ones that parasitize leafminers)…
…this ~2-mm agromyzid fly, which I think is something in the Phytomyzaatomaria species group; possibly P. crassiseta, which mines leaves of speedwells (Plantaginaceae: Veronica spp.)…
…still more dark-winged fungus gnats…
…a ~1-mm encyrtid wasp…
…another eulophid wasp, maybe the same as before…
…this click beetle (Elateridae: Melanotus)…
…this figitid wasp, which would have emerged from some kind of fly puparium, but it doesn’t look like the ones I rear from agromyzids; we’ll see what Matt Buffington has to say about it, eventually…
…another wolf spider…
…and finally, between June 4 and 10, nine of these ~2-mm frit flies (Chloropidae: Rhopalopterum):
I might not have thought much of these frit flies, but as it happens, in early April I split open a phlox stem right next to the garage and found three fly larvae near the base. They weren’t producing distinct tunnels as the Melanagromyza larvae do, but definitely living inside the stem.
All three formed puparia between the two layers of the piece of double-ply toilet paper I stuffed into the bottom of the vial I collected that chunk of stem in, and they emerged as adults between May 19 and 23.
To me they looked the same as the nine flies that emerged from the bagged phlox plants, and I sent them all to George Foster, who happens to be working on a revision of the genus Rhopalopterum. He agreed that they are all the same, and last I heard he was thinking they are a new species—the only new species he had encountered in the course of his revision. I will post an update when we have the last word on that, but I’ll add that I think this species has more than a casual association with garden phlox, because in July 2017, when I was investigating the leaf mines in my mother’s garden that turned out to be the work of the agromyzid that Owen and I later named Liriomyza phloxiphaga, I collected a few tiny flies that I found resting on the leaves, thinking they might be agromyzids—and they, too, turned out to be this same Rhopalopterum species.
When I decided to start working on a guide to North American sawfly larvae, the first thing I did was put together an updated list of all the species that occur here (the most recent list was published in 1979), so I could start taking stock of what was known about the host plants and larvae of each species. With this list completed, I discovered that there were eleven pairs of species that had identical names, all the result of a paper published ten years ago* that did away with several genera—including Amauronematus, Eitelius, Pachynematus, Pikonema, Pontania, Pteronidea, and Phyllocolpa—and declared them synonyms of the now enormous genus Euura, which now includes over 25% of the North American species in the largest sawfly family, Tenthredinidae. This is a shame, because many of these genera were convenient groupings; for instance, larvae of Pikonema species ate spruce needles, Pontania species all made round leaf galls on willows, Phyllocolpa species made leaf-fold galls on willows and poplars, and as previously defined, Euura contained two subgenera, of which one formed willow bud galls and the other formed willow stem galls.
In any case, when a similar change was made with agromyzid flies, lumping Chromatomyia and some other genera in with the now enormous genus Phytomyza, the paper that did so** included a complete list of all the world’s Phytomyza species and established new names to deal with the ten pairs of species that now had identical names as a result of this change. It seemed like no one was planning on doing this for the sawflies anytime soon, so one day last year I dashed off a little paper to take care of it myself, and that was just published yesterday***. All of the new names are based on the original ones; some are meaningless anagrams and for the rest I just changed the endings, as follows:
Amauronematus orbitalis Marlatt, 1896 →Euura borilista Eiseman
Euura minuta MacGillivray, 1914 →Euura untima Eiseman
I have never met any of the above species, but there was one more change I needed to make, and it involved a species I’ve found in my own front yard—the third type of sawfly larva I found in 2020 when I kept a running list of all the sawfly larvae and leafminers in my yard. I found five of these larvae munching on leaves of a bigtooth aspen sapling on May 31…
…All of them burrowed into a jar of soil the next day, and emerged as adults like this one the following spring:
Dave Smith identified these adults as the species that Marlatt had described as Amauronematus dyari in 1896 (named after Harrison Dyar, who is apparently the only person to have reared this species before me). When Dave put together the 1979 sawfly list, he placed this species in the genus Nematus, and because Marlatt (1896) had named another species Pteronus dyari that was later determined to be a synonym of Nematus latifasciatus Cresson, 1880, Dave established a new name for Amauronematus dyari, Nematus attus. The recent checklist of Canadian sawflies**** listed this species as Euura attus, as does the Electronic World Catalog of Symphyta, but this is incorrect: Dave’s replacement name is no longer necessary, because while this species has been transferred to Euura, N. latifasciatus (and therefore its synonym Amauronematus dyari) is still placed in the genus Nematus. So according to the rules of the International Commission on Zoological Nomenclature, the species in my yard must now go by the name Euura dyari.
I never thought I’d get mixed up in this kind of nomenclatural shenanigans, but as it happens I also felt compelled to rename a spider in another little paper that was also published yesterday*****. I wrote about this species ten years ago, and it is responsible for this egg sac, which I found on the underside of a board on Nantucket:
In 1884, H. C. McCook coined the name Micaria limnicunae for this spider, but his description—which applied only to the egg sac and the spiderlings that emerged from it—was considered “worthless” by arachnologists, and M. limnicunae has been treated as a name that can’t be attributed to any known species. However, for reasons explained in my paper, I am now convinced that this is the same spider that N. Banks described in 1892 as Agroeca ornata. I therefore have declared that the correct name for this spider is Agroeca limnicunae, and A. ornata is a junior synonym (and therefore should no longer be used). In this paper I also reveal that the maker of the mystery egg sac at the top of this post is Agroeca pratensis, and that also goes for the one on page 45 of Tracks & Sign of Insects and Other Invertebrates that is attributed to “Micaria limnicunae.” (My paper also discusses the mystery egg sac that was discussed on pp. 42–43 and here, concluding that the genus Tetragnatha is in need of revision and that arachnologists ought to take egg sac characteristics into account when working out the species limits.)
And while we’re getting caught up on taxonomic matters, I should mention that I wrote or co-wrote the sections on Bucculatricidae, Gracillariidae, Heliozelidae, Nepticulidae, Opostegidae, and Tischeriidae in the new checklist of North American Lepidoptera that was published a few months ago******, in which Erik van Nieukerken and I declared the poplar leafminer Stigmella aromella (Nepticulidae) a synonym of S. populetorum, and Don Davis and I declared the beech leafminer Phyllonorycter restrictella (Gracillariidae) a synonym of the European species P. maestingella, and the magnolia leafminer Phyllocnistis magnoliella a synonym of the tuliptree leafminer P. liriodendronella. Which brings us to the sad fact that I have now subtracted more species from the list of known North American moths than I have added. And, as it happens, one of the three moth species I have named–this little beauty, Grapholita thermopsidis (Tortricidae)…
…has had its name changed to the much less pronounceable Ephippiphora thermopsidis after the new checklist came out*******.
There are, of course, hundreds of leaf-mining moths that have yet to receive their first name, but unfortunately dealing with those requires a great deal more effort than shuffling around the names of the ones that have already been described.
* Prous, M., S. M. Blank, H. Goulet, E. Heibo, A. Liston, T. Malm, T. Nyman, S. Schmidt, D. R. Smith, H. Vårdal, M. Viitasaari, V. Vikberg, and A. Taeger. 2014. The genera of Nematinae (Hymenoptera, Tenthredinidae). Journal of Hymenoptera Research 40: 1–69. [Available online here.]
** Winkler, I. S., S. J. Scheffer, and C. Mitter. 2009. Molecular phylogeny and systematics of leaf-mining flies (Diptera: Agromyzidae): delimitation of Phytomyza Fallén sensu lato and included species groups, with new insights on morphological and host-use evolution. Systematic Entomology 34: 260–292. [Available online here.]
*** Eiseman, C. S. 2024. New names for Nearctic species of Euura Newman (Hymenoptera: Tenthredinidae). Proceedings of the Entomological Society of Washington 125(2) [2023]: 264–267.
**** Goulet, H. and A. M. R. Bennett. 2021. Checklist of the sawflies (Hymenoptera) of Canada, Alaska and Greenland. Journal of Hymenoptera Research 82: 21–67. [Available online here.]
***** Eiseman, C. S. 2024. On the identities of some distinctive, suspended spider egg sacs (Araneae: Liocranidae, Tetragnathidae). Proceedings of the Entomological Society of Washington 125(2) [2023]: 278–284.
****** Pohl, Gregory R. and Stephen R. Nanz (eds.). 2023. Annotated Taxonomic Checklist of the Lepidoptera of North America, North of Mexico. Wedge Entomological Research Foundation, 580 pp. [Print book; available for purchase here.]
******* Hu, G.-L., J. Brown, M. Heikkilä, L. Aarvik, and M. Mutanen. 2023. Molecular phylogeny, divergence time, biogeography and trends in host plant usage in the agriculturally important tortricid tribe Grapholitini (Lepidoptera: Tortricidae: Olethreutinae). Cladistics 39: 359–381. [Available online here.]
I just noticed that I never bothered to mention here that I finished the second edition of Leafminers of North America last December. Apparently I quietly updated the page dedicated to that book and then went back to working on other writing projects, including my guide to sawfly larvae and various papers on leafminers and other herbivorous insects. Of course all of the leafminer book subscribers received the last installment of the second edition at that time, and I sent out the first monthly installment of the third edition last month. So if you’ve been meaning to subscribe, now is a good time! Details are on that page (or you can click the image of the book cover below), and it’s still true that you can have the whole first edition for as little as $5, as explained here.
Also, someone just asked if there will be a calendar this year, and yes, a box of them is on the way to me right now! As usual, I will send a copy to anyone who makes a donation of at least $30 (the amount WordPress charges me each year to keep this blog free of annoying ads) before the end of November, which you can do here (select “Send,” and then include your mailing address in the notes). In this year’s calendar, some months have a single full-page photo and some show an adult leafminer along with its larval mine.
Also, I will be back at Eagle Hill in Maine next summer, teaching a week-long “Leaf and Stem Mining Insects” seminar the week of August 4. Their 2024 schedule isn’t on their website yet, but I suspect it isn’t too early to get yourself a spot if you contact them about it.
And also, one reason that things have been pretty quiet on this blog lately is that earlier this year, Julia and I had a baby girl, Ayla (pronounced eye-la). But the main reason is that this summer, we took Ayla on a six-week road trip—during which she got to meet two other baby girls at the International Congress of Dipterology in Reno, Nevada, where I was invited to speak about leaf-mining flies, and she also got to hang out with some moth people at the Lepidoptera Course at the Southwestern Research Station in Arizona, where I invited myself to visit and speak about leaf-mining moths on our way home—and as a result I’ve been extra busy with work (and bug rearing projects) ever since. Here’s Ayla examining a columbine flower in Arizona and an “oak apple” gall in Oklahoma (she determined the latter to be crunchy and full of ants):
Now the reports I had to do for other people are in, and almost all of my bugs are put away in the fridge for the winter, so I expect BugTracks will become a little more active as I go through all my photos from this year. In the meantime, if you know your western and midwestern plants, I’d appreciate any help you can offer identifying the hosts of the leafminers I found this summer, which are all posted on iNaturalist. I’m slowly getting caught up with reviewing everyone else’s leafminer observations in the Leafminers of North America project; I’m up to early September now, with just 4300 or so left to go! iNaturalist’s “computer vision” AI has improved greatly in recognizing leafminer species, so that I now can often select the correct identification from a dropdown list of its top guesses, but of course what makes things most efficient is when the (human) observer has made an informed identification (e.g. by using my book) and all I have to do is click “agree” and move on. One of the projects I’m currently focusing on is another big paper on agromyzid flies with Owen Lonsdale, which will include a number of new host records, new distribution records, and new species based on specimens that various iNaturalist users reared when I asked them to follow up on some particularly interesting finds.
Okay, I think those are all my announcements for now!
You know those hairs that line the basal portion of the midrib on the lower surface of black cherry (Rosaceae: Prunus serotina) leaves?
Or the ones in the vein axils on the lower surface of many other tree leaves, like this black oak (Fagaceae: Quercus velutina)?
It turns out these are Acarodomatia! Which is to say, they are structures that evolved for the purpose of housing mites that benefit these plants, either by preying on tiny herbivores (e.g. other mites) or by feeding on pathogenic fungi. I just heard about this for the first time last night when James Trager accidentally sent me a message on Facebook, which caused me to see a link he’d sent me four years earlier that I’d missed until now. (Tip: if you want me to see something, send me an email; I often miss things on Facebook messenger. If you want to make sure I never hear something, leave me a voicemail.) That link was to this “In Defense of Plants” podcast, which I listened to last night; it features Gussie Maccracken talking about her work with fossils, including this paper that gives evidence of acarodomatia already existing around 75 million years ago. Googling “acarodomatia” turns up lots of other information, including this review paper which says (among other things) that these structures are found in about half of North American tree species. I’m a little annoyed that I spent almost 20 years in school and no one ever mentioned the existence of these things.
So, today I walked around the yard and plucked a few leaves that had acarodomatia on them, including the two pictured above, and had a look at them under the microscope. I didn’t see anything among the hairs of the black cherry leaf, but they provide an extensive hiding place and it would be easy to miss any mites that may have been there. When I looked at the ones in the black oak vein axils, I saw a little colorless mite go scrambling out of the second one I looked at, and the same thing happened with the third—I think they were disturbed by the intense light under the scope. I was unable to relocate them when I trained my camera on them, but I believe the spherical object at the center of this photo is a mite egg:
Leaves of striped maple (Sapindaceae: Acer pensylvanicum), it turns out, have nice cavernous retreats in the vein axils behind these hairs. There are several pairs of these acarodomatia along the length of the midrib.
The red maple (A. rubrum) leaves I looked at just had a single pair of tufts at the base of the midrib. This restricted real estate, it seems, improved my chances of spotting the resident mite. See it?
Okay, it’s pretty subtle, given that it’s extremely tiny (~0.2 mm long) and hiding behind a couple of hairs. Here’s a closer crop:
I got a few other photos of it as it ran around on the leaf veins; they’re certainly not good, but maybe sufficient for an acarologist to tell us approximately what kind of mite it is:
So, as with extrafloral nectaries, these acarodomatia are common structures that are often mentioned in botanical manuals (hairs in the axils of veins noted in this key, for instance), but bafflingly, no one ever bothers to point out what their purpose is.
It’s normally a little disappointing to find an ichneumon wasp in one of my rearing containers, since that generally means I failed to rear whatever insect I was trying to rear. So when this one appeared yesterday…
…I braced myself for the bad news as I checked the lid of the jar to see what sawfly larva I had collected sometime last year, kept provided with fresh leaves of its host plant, given a jar of soil to burrow into, and refrigerated over the winter, only to have it succumb to a parasitoid, leaving its identity as mysterious to me as if I had just taken a photo of it on the plant and left it to its fate. But I found that what I had scribbled on the lid was “10/1/22 hazelnut, parasitized, gone 10/2.” Which meant that I already knew it was parasitized when I collected it on October 1, and it burrowed into the soil by the next day—so not a big loss, and a minimal investment of effort on my part. As it happens, I had just made it up to October 1 in sorting through the photos I took last year, so I was able to quickly refresh my memory about who this sawfly larva was. But before I get to that, a little background on the hazelnut sawflies in my yard.
Although there are native beaked hazelnuts (Betulaceae: Corylus cornuta) growing wild around the edges of the yard, it is the hazelnuts we planted—Corylus ‘Medium Long’, which is thought to be a hybrid of American hazelnut (C. americana) and the European hazelnut (C. avellana)—that always seem to attract the sawfly larvae. Just about every year, these larvae show up and get to work defoliating them:
Both of the above photos were taken on September 2, 2016, and at the time I thought I was seeing different-aged larvae of the same species—in fact, they were filed together until today, when I realized the smaller larvae in the top photo belong to a different family (Tenthredinidae; tribe Nematini) from the spotted larva, which is in the family Argidae. It was the spotted larvae that I succeeded in rearing; adults emerged the following June, and Dave Smith identified them as Arge willi.
When I did a thorough inventory of the sawfly larvae in my yard in 2020, larvae of the first type showed up on June 21. I collected them but again failed to rear them; four parasitoids in the genus Ichneutes (Braconidae) emerged the following March.
And I found larvae of Arge willi starting on September 1.
Then, on October 10, I found this beauty (which is something in the subfamily Tenthredininae)…
…but I failed to rear it as well. I looked in vain for more larvae like this in October 2021, and then again this past October. Although no yellow-spotted larvae materialized, I did find yet another species that I hadn’t seen in my yard before.
I think these may be Hemichroa crocea, which normally feeds on alder (Alnus) but is occasionally found on birch (Betula) and hazelnut (Corylus). I was just about finished writing my key to birch-feeding sawfly larvae this winter when I turned my attention to a taxonomic paper on tischeriid moths, but hazelnut will be the next key I do when I get back to that project (well, after musclewood (Carpinus), as I work my way alphabetically through the birch family). Anyway, on the same bush as the larvae above, I found this one, which (based on my knowledge of birch-feeding sawflies) I believe is a Nematus species.
I saw the objects attached to its head and thorax and knew it was unlikely to survive, but I decided to collect it anyway. Ichneumon wasps in the subfamily Tryphoninae attach stalked eggs to their hosts, and I think that’s what the brown object on the head is. As for the white object on the thorax, I believe it is a larva rather than an egg, but whether it’s a tryphonine or something else, I’m not sure.
In this view, the stalk on the egg is more apparent:
I think the ichneumonid that emerged yesterday is in fact a tryphonine, but someone please correct me if I’m wrong. And its sawfly host may have been Nematus corylus; for comparison, here are some larvae of that species that Julia and I collected on Nantucket in September 2020…
…and an adult that emerged the following April:
Looking back through my photos, I think N. corylus was probably the host of the braconids, and it may have been the species that I initially mixed up with Arge willi, but I don’t seem to have photos of those larvae in later instars. Once I put together my key to larvae on hazelnut I’ll have a better sense of how many (known) options there are for larvae with that general appearance. In any case, it’s nice to have our hazelnut bushes providing food for at least four different sawfly species, in addition to occasionally giving us some nuts to eat.
Back in 2012, when I had only recently realized I needed to write a complete guide to the leafminers of North America and as a result Julia and I were driving around the US to find them all, we visited a friend of mine from college, Josh Lane, in Bonny Doon, California, which is a little south of San Francisco. The three of us took a walk on a drizzly Halloween morning, and the first leaf mines we noticed were on a plant that Josh informed us was yerba santa (Namaceae: Eriodictyon)…
…which made it easy to identify the maker of the mines as Phytomyza eriodictyi, an agromyzid fly.
Apparently it wasn’t a very productive walk, based on the photos I took that day, because it was over a half an hour before I pulled out my camera again, and that was to photograph not a leaf mine but an elaborate web of an orbweaver in the genus Metepeira (Araneidae), consisting of a typical spiraling orb web next to a labyrinth of crisscrossing threads, near the top of which the spider had constructed a retreat out of bits of leaves and other debris, in which it was now waiting for insect prey to become caught in the web.
Fifteen minutes later, we stopped to examine one of California’s zillion species of Ceanothus (Rhamnaceae), which had mines of three different moth families on display.
This elongate mine that caused the leaf margin to curl over and conceal it was made by a Tischeria species (Tischeriidae); a lot more work needs to be done on this group, and if anyone out there is interested in rearing adults and sending them to me, I would love to check them out.
Linear mines on Ceanothus are made by Nepticulidae; I still don’t know how to distinguish mines of Acalyptris punctulata from those of the several Stigmella species on these plants. Another good project for someone.
And then there were the distinctive mines of Xenolechia ceanothiella (Gelechiidae), each consisting of a branching track with a tubular retreat of silk spun just outside the entrance on the lower surface.
A few minutes later we arrived at a seepy spot that I dimly recall as being our destination for this walk—I think Josh wanted to show us this plant, and I don’t remember now if it was because he had noticed mines on it or just because it was a neat plant that was in bloom then, but in any case he evidently didn’t know what it was because in my journal it’s just referred to as “Bonny Doon scroph,” as in, what used to be the snapdragon family (Scrophulariaceae) before most of its species were moved to other families including Orobanchaceae, Phrymaceae, and Plantaginaceae. I later learned that the plant was musk monkeyflower (Phrymaceae: Erythranthe moschata, formerly Mimulus moschatus), which also exists back home in Massachusetts, where it is rare and protected as a Threatened species.
Some of the leaves were riddled with linear mines, which had the general look of fly mines, with grains of frass along the sides, or at least not forming a central line.
Upon picking the leaf in the photo above and flipping it over, I could see a larva inside one of the mines, and it was much more elongate than a typical agromyzid fly larva. It’s at the top center in the photo below.
Looking more closely, it had a definite head capsule, unlike any of the usual leaf-mining fly larvae.
On a nearby leaf, we found a larva in the process of establishing a new mine, lying on the upper surface with just its front end inserted below the epidermis.
These seemed to be midge larvae (Chironomidae), which are normally aquatic, and are not normally leafminers; the only remotely similar phenomenon I was aware of was the mine-like channels that Polypedilum braseniae makes in floating leaves. We speculated that the wet weather had provided the opportunity for these larvae to venture up out of the seep and into normally inaccessible leaves. After spending 15 minutes with this mystery, and sticking a few leaves in a vial with the hope of rearing an adult, we finished our walk, and Julia and I continued on down the California coast.
Three days later, I took this photo of one of the larvae worming around along the wall of the vial…
…And two days after that, I could see a couple of pupae among the leaves in the vial. Here’s one:
And the other, with its shed larval skin (exuviae) visible to the right.
A month later, no adults had emerged, and when writing to Ray Gagné about some of the interesting gall midges we had found on our trip, I asked him if he could suggest anyone who might know about these leaf-mining midges. He referred me to Peter Cranston, who he noted is based in Australia but had spent many years in California. Peter in turn referred me to John Epler as the go-to person for information on Chironomidae in the US, but in Peter’s reply, he wrote:
Was the yellow-flowered scroph a Mimulus by chance ? I have seen grazing like this on leaves essentially in the splash zone but without contents. There is a diffuse literature on leafmining in chironomids, but most refer to immersed leaves. As for terrestrial leaves there are reports of some orthoclads from Brasilian rainforests, but I do not recall if the observations are formally published and related to an identified taxon. Many years ago I was sent a larvae from Australian rainforest but it may have been developing in a mucous blob rather than truly mining.
John (who lives in Florida) was unfamiliar with this midge, but agreed that it looked like a chironomid and he offered to examine the pupae, instructing me to be sure to preserve the larval exuviae as well. He listed a number of chironomids that do something that might be considered leafmining, but none of them out of the water, and after thoroughly scouring the literature, I have only come up with four species worldwide that have been documented as true miners (living between the two epidermal layers and feeding on the excavated tissue) of living leaves; all of them are in the genus Cricotopus and mine in floating or submerged leaves of pondweeds (Potamogetonaceae: Potamogeton).
After an intensive search of the leaf mush in the vial, I could only find one of the pupae, but I did manage to locate the larval exuviae. When I sent these items to John, he said there was no pupa, just a piece of leaf with a seed stuck to it, but he was able to slide-mount the larval skin and determine that it belonged to the genus Metriocnemus (which is in the subfamily Orthocladiinae, so related to the rumored terrestrial leaf-mining midges from Brazil).
I have not personally encountered a leaf-mining midge since, but five years later (in June 2017) John van der Linden found some midge larvae mining in water speedwell (Plantaginaceae: Veronica anagallis-aquatica) in Iowa. He reared three flies from these leaves, which included Scaptomyza pallida (Drosophilidae)—a species I have reared several times as a secondary inhabitant in mines, leaf rolls, and other damaged plant tissue caused by other insects—along with two midges. John Epler was too busy to examine more specimens at that point, but I asked around and found a midge specialist in Canada, Armin Namayandeh, who was happy to help when John van der Linden wrote to him. Unfortunately, both were females and as a result could not be confidently identified, but Armin reported that both appeared to be in the genus Bryophaenocladius but represented two different species.
Late the following January, John found some more of these Veronica miners and decided to try and rear them again. This time, in addition to the larvae that were making the mines—which looked similar to the ones I had found in California—he noticed a smaller, darker larva moving around in one of the mines, nibbling here and there along the edges; he suspected this was a secondary inhabitant.
He preserved that larva, and Armin determined that it belonged to the genus Limnophyes; he also reexamined the two adult females and realized that they were likewise Limnophyes, based on lanceolate setae on the thorax that he had neglected to note when he first looked at them. John also reared a couple of adult males, which Armin identified as Metriocnemus eurynotus, a species whose larval habits had never been reported.
But back to monkeyflowers: they turn out to be the study organisms of Kathy Toll, the partner of Eric LoPresti, who was an intern at the Nantucket Maria Mitchell Association along with Julia when we first met on Nantucket in the fall of 2011. In June 2019, Kathy found some midge mines on seep monkeyflower (Erythranthe guttata) growing along the California coast, and although I was again unable to rear any adults, I was able to preserve one larva.
Another two years passed, and then in March 2021 Mike Palmer sent me a photo of a leaf mine on seep monkeyflower that he’d just found on his land in Oregon. He had no idea this mine would be of particular interest to me, but he was excited because it was the first mine of any kind he had found there since the Holiday Farm wildfire had devastated the area a few months earlier. He had retired from his position at Oklahoma State University and moved to Oregon full-time, just in time to have his home destroyed and the entire property scorched and covered in ash. The vertical rock face where the monkeyflowers and various other herbaceous plants appeared that spring—along with the leafminers—had been covered by a dense bryophyte layer before the fire.
Two months later, Eric (who had just taken over Mike’s old position at Oklahoma State) and Kathy found some mines on roundleaf monkeyflower (E. glabrata) in Oklahoma.
At last, this time we succeeded in rearing some adults.
I sent them (and associated larval and pupal exuviae) to Armin, along with Kathy’s larva from California, and after comparing them with the description of every other Metriocnemus species in the world, he determined that they represented a new species, which we decided to name M. erythranthei. He borrowed the slide that John Epler had prepared of the larva I had collected back in 2012, and he confirmed that it (like Kathy’s larva) was the same species.
Now that this monkeyflower midge was finally going to get a name, last spring I encouraged Mike to try rearing some so we could be sure that what he had found in Oregon was the same species, and I also encouraged John van der Linden to do some more rearing from water speedwell. Unfortunately the whereabouts of his specimens mentioned above is currently unknown; Armin moved from Ontario to Michigan in the intervening years and hasn’t been able to relocate them so far. Both Mike and John were successful, and then some: even though Mike didn’t yet have a lab setup or even a permanent living space, he managed to rear a bunch of adults from monkeyflower almost immediately, and he also collected larvae and pupae, and reared a few adults, from a number of different plants on that same seepy rockface: Siberian spring beauty (Montiaceae: Claytonia sibirica), forget-me-not (Boraginaceae: Myosotis scorpioides), Arctic sweet coltsfoot (Asteraceae: Petasites frigidus), coastal hedgenettle (Lamiaceae: Stachyschamissonis var. cooleyae), and mint (Lamiaceae: Mentha × piperita ssp. citrata)—not to mention from Veronica americana, the native relative of water speedwell, at a nearby site. John reared more adults from water speedwell, and at the same site in Iowa found different-looking midge larvae mining in jewelweed (Balsaminaceae: Impatiens) cotyledons. Just to make things extra confusing, he also found some of these larvae feeding inside the Metriocnemus mines on water speedwell:
Meanwhile, with the exponential growth in popularity of documenting leaf mines on iNaturalist, observations of these midge mines started popping up all over the place, and I got several people to collect specimens for Armin to examine: Finn McGhee collected a pupa from seep monkeyflower in British Columbia; Jeff Ward reared a female from Siberian spring beauty in Oregon; and Cecil Smith collected larvae from water speedwell in Pennsylvania.
The verdict? The miners in monkeyflowers and speedwells from the west coast to Pennsylvania are all the same new species, Metriocnemus erythranthei. South and east of Oregon, there is no evidence of this midge feeding on any other plants, but in Oregon it mines in Siberian spring beauty and all those other plants from which Mike collected larvae. Mines that seem likely to represent the same species have been found on an even wider array of plants in British Columbia and Alaska. Incidentally, I’ve noticed the opposite situation with Liriomyza schmidti, one of the most polyphagous of all agromyzid flies. Until recently, it was only known to occur in the Neotropics north to southern Florida, but Tracy Feldman has reared it in North Carolina and iNaturalist observers have found mines north to the DC area and west to Texas. Although it occurs on dozens of different plant families in Florida and South America, it has been found on just a few plant species farther north, mainly greenbriers (Smilacaceae: Smilax) and passionflowers (Passifloraceae: Passiflora).
John’s purple-striped jewelweed-mining larvae, which he also found in mines of M. erythranthei in water speedwell, are M. eurynotus. (It is unclear at this point whether the adults Armin initially identified as M. eurynotus were this species or M. erythranthei, because the two are very similar.) Whereas M. erythranthei larvae are leafminers throughout their development and pupate in their mines, older larvae of M. eurynotus feed on leaves externally, and it is not entirely clear whether they are able to establish mines in pristine leaves or whether there was some kind of initial damage that allowed them to enter the jewelweed cotyledons. Mike also collected M. eurynotus larvae together with M. erythranthei on Arctic sweet coltsfoot in Oregon.
To further complicate things, Mike also collected larvae from Arctic sweet coltsfoot, Siberian spring beauty, and forget-me-not that had purple banding just on the first two body segments; these belong to a Metriocnemus species that is as yet unnamed because no adults have been reared. Because Mike was not able to make detailed observations of these collections, it was not clear to what extent these larvae were mining the leaves versus feeding on the surface, but just the other day I came across this seven-year-old observation of what appears to be the same species on twistedstalk (Liliaceae: Streptopus) in Alaska. That larva was initially found feeding in a leaf mine, but some time after it was collected it was photographed feeding on the surface as with later instars of M. eurynotus.
And what about those Limnophyes species that figured prominently in John’s initial discovery of the water speedwell mines? Well, Mike reared over 20 adults of a new species in this genus from his collection of monkeyflower mines, and the larval exuviae seem to match the larva from John’s first video. Of the two females John had reared, this one appears to be the same species. Last year John also reared one male of this species from his collection of jewelweed cotyledons, and a few days earlier he had observed what may have been a larva of this species feeding in one of the mines along with a larger larva of M. eurynotus. Mike suggested the name Limonophyes viribus, a reference to a phoenix sculpture named Viribus (Latin for “strength”) that was erected in the town of Blue River after the devastating fire.
All this, and much more, is documented in our paper that was published yesterday:
Eiseman, Charles S., Armin Namayandeh, John van der Linden, and Michael W. Palmer. 2023. Metriocnemus erythranthei sp. nov. and Limnophyes viribus sp. nov. (Diptera: Chironomidae: Orthocladiinae): leafminers of monkeyflowers, speedwells, and other herbaceous plants, with new observations on the ecology and habitats of other leaf-mining Chironomidae. Zootaxa 5249(1): 41–68.
I optimistically included “Part 1” in the title of this post, because I hope someday there will be a “Part 2” in which we give a name to that other new species of Metriocnemus and work out its life history, confirm the identity of the midges mining all those other plants in Alaska, have more to say about that other Limnophyes species John reared (including what its larva looks like), and ideally document the whole life cycles of all these species. At this point we don’t know where any of them lay their eggs, and for the Limnophyes species it is unclear where they pupate, whether they are obligate associates of Metriocnemus, and if not, what they do when they aren’t feeding in Metriocnemus mines.
Simply not mowing the lawn, and welcoming whatever plants decide to grow in its place, has done wonders for the biodiversity of our yard. But we have also welcomed gifts of native plants from friends, and today I’d like to shine a light on a silky willow (Salicaceae: Salix sericea) shrub that Adam Kohl gave us a couple of years ago. We planted it in a moist spot at the edge of the woods, and last year it was discovered by several insects I hadn’t seen in the yard before. The first I noticed was this sawfly larva, which appeared on May 27:
Although I’ve made some good progress on my guide to sawfly larvae this winter, I haven’t yet tried to make a key to the willow-feeding species—and I think there are more sawflies on willows than on any other plant genus—so for now all I can say is that this is something in the subfamily Nematinae (Tenthredinidae). I of course collected it to see if I could rear it to an adult, and the next day it turned purple, indicating that it had entered the non-feeding prepupal stage.
I put it in a jar of soil, since most sawfly larvae burrow into the ground to pupate, but after wandering around for two days it spun a cocoon between two leaves.
So far, no adult has emerged; maybe one will when I take all my overwintering bugs out of the fridge in a few days.
When I visited the silky willow on June 2, I noticed evidence of a leafminer I hadn’t seen in my yard before:
A larva of Caloptilia stigmatella (Gracillariidae) had made a little underside tentiform mine in one leaf, then moved to a fresh leaf and used silk to roll the tip into a cone, where it was now feeding on the leaf externally, but within the shelter of the cone (as is typical of Caloptilia species). Both the mine and the cone were more conspicuous from below:
Caloptilia stigmatella has been reared from a variety of willows and poplars, but I have seen no records of it from silky willow, so I collected the leaf with the cone to make absolutely sure it was that species. Six days later the larva finished feeding and spun a cocoon:
Alas, before I discovered the Caloptilia larva, an ichneumon wasp had already laid an egg on (or in) it, and a week and a half after the cocoon was spun, her daughter emerged from it:
Meanwhile, on June 12 I noticed some more underside tentiform mines on the silky willow, but these were larger and more “tented,” indicating they were made by some species of Phyllonorycter (also Gracillariidae) instead of Caloptilia. Phyllonorycter species complete development in their mines instead of exiting to feed in leaf rolls.
If you tried to identify these mines using my key to willow leafminers, you’d get to Phyllonorycter and would then find that you need a reared adult to get further, because the leaf mines of the willow-feeding Phyllonorycter species all look pretty much the same. So I collected this leaf, and adults emerged from both of the mines five days later, leaving their pupal skins poking out.
Now, if the antenna weren’t obscuring the white streak along the costal margin at the base of the wing, the key I made would correctly identify this as Phyllonorycter scudderella (which also has not been reported from silky willow before). However, the first step in Davis & Deschka’s (2001) key to Salicaceae-feeding Phyllonorycter species ignores all external features and asks whether or not the male genitalia have symmetrical valvae. Here’s the answer:
The left valva is big and broad and the right one is little and shrimpy, just as in Davis & Deschka’s illustration for P. scudderella, and from there their key easily takes my moth to that species based on wing pattern. (For whatever reason, I am unable to get photos in sharp focus using my compound microscope’s lowest magnification, so I took three photos at higher magnification and quickly spliced them together here.) A year ago I posted photos of the genitalia of P. nipigon, which has symmetrial, slender valvae; see that post and the previous one for some explanation of what dissecting these tiny moths involves.
Anyway, on June 12 I noticed an adult sawfly on the silky willow, and I thought it might be the same species as the larva I’d collected two weeks earlier…
…but it turned out to be Thrinax dubitata (Tenthredinidae: Selandriinae), whose larvae eat sensitive fern (Onocleaceae: Onoclea sensibilis). Which makes sense, because there is lots of sensitive fern all around that willow. But this adult sawfly was more than casually interested in the willow, and for quite a while after that, every time I walked by, I noticed that numerous very tiny wasps (~1 mm long) were also very interested in it, scurrying all over its leaves. On July 7 I finally got around to bringing my camera over and investigating what they were up to—as well as confirming my suspicion that they were playgastrids. They scattered each time I got the lens near them, but I managed to get five of them in the frame in one shot:
All platygastrids (as the family is currently circumscribed) are parasitoids of gall midges (Cecidomyiidae), and there were no midge galls in sight. So what were these little wasps up to? It only took a few moments of watching them to realize that they were drinking from extrafloral nectaries along the leaf margin. In the photo below, note that each of the leaf serrations has a round appendage on the left side, and each of these appendages has a little droplet of delicious honeydew bubbling out of it.
Here’s a closer view of three of these nectaries from the underside of the leaf, with the droplets coming out on the right side:
I had previously only noticed extrafloral nectaries on the petioles of leaves (like cherry), so this was all news to me.
Getting an in-focus photo of one of these wasps, as it briefly sipped from one nectary before moving on, was pretty challenging, but I at least managed to document them doing it.
As I explained in my previous post about extrafloral nectaries, the idea is that they attract predators such as ants, whose presence will result in fewer herbivorous insects munching on the leaves. I suppose it’s possible that these platygastrids could be helping the plant by defending it against gall midges, but galls don’t really impact the health of the plant and I think these wasps are pretty much freeloaders. There was, however, a big ol’ ant that came along to partake of the nectaries while I was trying to get pictures of the platygastrids.
And, in retrospect, that’s what the adult sawfly had been up to as well.
Obviously attracting sawflies isn’t necessarily what the plant is going for, since larvae of many species eat willow leaves, but adults of some species are predatory—in fact, here is one chomping on a platygastrid—and the yellow dusting on this one’s head and thorax indicate that it has also been visiting flowers for nectar, so it is a potential pollinator as well. As is so often the case, whether an insect is “beneficial” or “detrimental” is not so clear-cut here, and it makes no difference to me. The bugs that come to eat the plants, and the bugs that come to eat those bugs, are all equally welcome in my yard.
When Julia was in high school, she built this little cabin in the woods behind her family’s house in central Ohio:
One chilly morning last April, when we stopped there on our way to spending a week exploring the Ozarks, we took the door off the hinges so that its rotten bottom could be repaired (the result can be seen in the above photo). We carried it back to her parents’ driveway and laid it on the ground, with the inside facing up, and I was surprised to see a greater bee fly (Bombyliidae: Bombylius major) clinging to it.
I’ve rarely even attempted to photograph these flies because they are normally in constant motion as they buzz from one spring wildflower to the next like tiny hummingbirds. I guess they have to sleep sometime though, and this one hadn’t yet thawed out from the previous night’s freezing temperatures, so I was able to get a close look.
As the above photo makes clear, it was resting on the webbing associated with a cottony-textured spider egg sac. Fluffy ones like this are usually the work of either orbweavers (Araneidae) or cobweb spiders (Theridiidae). Right next to it was a smooth, disc-shaped egg sac like this one:
Egg sacs of this form are generally the work of hunting spiders (e.g. crab spiders) as opposed to those that spin webs to catch their prey. These particular eggs sacs had distinctive radiating “spokes” of silk around their margins. That may be indicative of a particular species, but I have no idea which one!
Also note that in the crack right next to the above egg sac, there is a web of a tube web spider (Segestriidae: Ariadna bicolor). These spiders wait in their tubes and dart out to grab passing insects that bump into the fine strands of silk that radiate from their entrances. Here are two more tube webs:
While I was taking pictures of all these things, some tiny, previously unnoticed bugs started to warm up enough to wander around on the door. One was this ~3.5 mm long moth:
This is Phyllonorycter celtifoliella (Gracillariidae), which as a larva forms underside tentiform mines in hackberry leaves. Most Phyllonorycter species seem to overwinter as pupae in their mines, but the one time I reared this species, the adult emerged in October. This one found under loose bark in Iowa in January confirms that this species overwinters as an adult. …Okay, it’s dead, but I’m pretty sure the photographer killed it to take the photo. Here is a live one that was among a group of 60 or so found in Nebraska in November, which “were tucked behind the bark of a dead oak tree and were hiding amongst the silk cocoon, larval and pupal exuviae, left over from a Giant Leopard Moth.” So I may have been witnessing this moth waking up in the spring for the first time, after having spent the winter behind the door of Julia’s cabin. (This was not the case for the bee fly, which overwintered as a pupa in the burrow of a ground-nesting bee.)
And wandering about among all of these things were numerous garden springtails (Bourletiellidae: Bourletiella hortensis), at most 1 mm long, which came in a variety of colors:
Beyond what lives behind the door to Julia’s old cabin, the woods immediately surrounding it are the type locality for Phytomyza aesculi and P. hydrophyllivora (Agromyzidae), and are also where I found this lovely moth that bores in Ohio buckeye petioles, and where I photographed a bunch of different bugs visiting narrow-leaved spring beauty flowers a few years ago.
Ever since I made a place on BugGuide to collect photos of them over a decade ago, I’ve been wanting to see (in person) one of those weird wingless gall wasps that can be found throughout the winter. Two years ago I put them on the “winter bug bingo” card I made for the online “Bugs in Winter” course I put together, and I think one participant managed to find one, but I wasn’t so lucky.
Last fall at the end of a game of tennis, I noticed a white oak leaf at the edge of the court with a couple of “oak pea galls” on it, like this one:
This gall is caused by Acraspis pezomachoides (Cynipidae), and knowing that Acraspis is one of the genera with wingless adults, I decided it was time to be a little more proactive in my quest to see one, so I took the leaf home and stuck it in a jar. But alas, I just got a couple of lousy parasitoids.
Last month, while leading a workshop on identifying invertebrate tracks and sign, I picked up a white oak leaf with an “oak hedgehog gall” on it—made by the related species Acraspis erinacei. It was already brown like the one pictured above, but here’s what a fresh one looks like:
I decided to try again, so after everyone had gotten a good look at the gall, I had Julia put it in her backpack.
A week or so ago, I remembered the gall and had Julia fish it out of her backpack. I put it in a vial on a shelf in my office, and every couple of days I’ve remembered to check the vial (most of my other bugs having been put away for the winter at this point).
Last night I checked, and there she was!
Here’s what the gall looked like after she emerged (the exit hole is at the bottom, near where it’s attached to the leaf).
The adults that emerge from round, faceted galls like this—provided that they are not parasitoids or inquilines—are all wingless females. Like most cynipids, Acraspis species have a two-part life cycle. These females climb up to white oak leaf and flower buds and lay eggs in them. Tiny, inconspicuous galls form in the buds (see examples at gallformers.org), and winged males and females emerge from these in the spring. After mating, females lay eggs in midribs of white oak leaves, and the galls that will produce the next set of wingless females develop over the summer.
Virtually all of the bugs I raise are unknowns that have to be killed and preserved to be identified, so it was nice, for a change, to raise one that already has a name and whose whole life cycle has already been worked out. This morning I took her out to a white oak sapling in the woods behind my house and set her on it, thinking maybe I’d get to see her lay some eggs.
No such luck; she didn’t seem to like this sapling, and started making her way down its stem. So I moved her to the trunk of the white oak tree that was right next to it. There, she decided to just sit and preen for a long, long time.
It was below freezing out and my fingers were getting cold, so I decided to leave her to it.
When I stopped to feed the chickens on my way in, I found another wingless weirdo waiting for me by the door of the shed: a female fall cankerworm moth (Geometridae: Alsophila pometaria). ‘Tis the season, I guess! Her eggs will overwinter, hatching in the spring into inchworms that will nibble the leaves of the apple or cherry tree overhead, from whence she presumably came.
More wingless wonders await—I’m always excited to find a snow scorpionfly or snow fly trudging across the snow in winter.
Oh, and tonight I checked the vial with the gall again and discovered that another Acraspis erinacei female has emerged. As noted on gallformers.org (which I highly recommend for identifying galls and reading up on what’s known about them), these galls may contain between two and eight central cells with individuals of A. erinacei (or their parasitoids) developing in them, as well as additional cells around the periphery with inquilines developing in them. Inquilines are (in this case) cynipid wasps that develop inside the galls induced by other cynipid wasps, without (necessarily) killing the original inhabitants. Twelve winters ago, before I knew anything about the life cycle of Acraspis species, I collected some A. pezomachoides galls from under a white oak tree, assuming that what emerged would be Acraspis adults, but instead I got nothing but inquilines, which emerged in early June—thereby skipping the alternate, bud gall-inducing generation of their host species, and appearing just in time to find some developing “pea” galls to lay eggs in. This one’s a male:
If you enjoy reading this blog, please consider making a donation. I would devote all my time to natural history writing and photography if I could! You can make a one-time donation using the yellow button above, or click the “Become a Patron” button to learn how you can support my work on a monthly basis, which gets you (among other things) monthly installments of my new leafminer book. To see other options for getting the book, click the image of its cover below.
To order either of my books, click on the images of their covers above.
For my Leafminers of North America project, I periodically need help identifying hostplants I find in my travels. You can peruse photos of them at iNaturalist. Thanks!
BugTracks 