Silk on Stink Bug Eggs, Part 2

In my last post I wrote about a little wasp in Mexico that apparently spins silk over stink bug eggs after it inserts its own eggs inside them. Several people had told me confidently that it was a pteromalid, so I went with that. However, shortly after I published my post, Henry Hespenheide wrote:

I think the parasitoid is a eurytomid.  Note the very large pronotum which is characteristic of the family.  And a number of the genera have the wings infuscated like the ones you show.  One of the subfamilies, Rileyinae, are egg parasitoids.

To be honest, I had thought it looked like a eurytomid too, but “it kinda looks like a eurytomid” is about as sophisticated as I get in identifying micro-wasps before appealing to someone else for help. What I was seeing, besides the general shape, was that it was rough-textured and black, just like most of the eurytomids I’ve reared from galls. For instance the one below, which came from a goldenrod rosette gall made by a fruit fly (Tephritidae: Procecidochares):

IMG_4806 That one had been having trouble getting the antenna portion of its pupal skin off, but had just succeeded in removing the right “sleeve” when I took that photo.

Anyway, I guess the fact that I had only ever encountered eurytomids as gall parasitoids had kept me from considering that this stink bug egg wasp might be one. But as pointed out here, eurytomids have a wide variety of habits, and many even have vegetarian larvae that develop in seeds or stems. In fact, here is one I found in my yard this spring, a member of the genus Tetramesa, whose larvae are known as “jointworms” and cause galls in grass stems.


I only just learned that a few weeks ago, but my brain is so full of leafminers right now that everything else gets pushed out. Speaking of which, some eurytomids in the Neotropical genus Aximopsis are parasitoids of leaf-mining beetles (Buprestidae).

Anyway, I followed Henry’s advice and showed my last post to Mike Gates, the eurytomid specialist at the Smithsonian National Museum of Natural History. Mike confirmed that the wasp in Cheryl’s photos and videos is a eurytomid in the genus Neorileya, and said he would be interested in seeing specimens. He has never heard of Neorileya producing silk, and is interested in more concrete proof that this wasp was actually responsible for the silk, since we can’t actually see the wasp laying down silk in the videos, nor was Cheryl able to see silk coming out of the tiny wasp.

To me, the fact that Cheryl photographed the wasp on the egg mass over a period of several days, during which the silk covering gradually increased, is pretty convincing. There’s also this: right after I published my last post, Kelly, who had sent the photo of the original silk-covered egg cluster from Brazil, wrote to tell me that she had found another silk-covered stink bug egg cluster with a similar wasp on it:


Unfortunately the wasp flew away after she took several pictures, but she collected the egg mass and will save anything that emerges from it. Stay tuned…

Edit: Kelly just found another photo of a similar wasp taken in Brazil, here. As with Kelly’s photo above, the silk is in bands that stitch the eggs together, rather than covering them in a web as in Cheryl’s example from Mexico.

The photographer, Bruno Garcia, gave me permission to use his photo here, but if you want to see a larger version you can click the above link.


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Silk on Stink Bug Eggs

Last week I got an email from a reader named Kelly in Brazil, asking if I could help unravel the mystery of these stink bug eggs (Pentatomidae) covered with silk:


I was at a loss, and simply responded: “Interesting find… I’m not aware of any true bugs (Hemiptera) that produce silk, so I think the silk must have been put there by something else (a spider?).  As to why something would spin silk over pentatomid eggs, I couldn’t say!”

Three days later, I got a note from Cheryl Harleston, who wrote:

I’m a  friend of the girl from Brazil who just sent you a photo of stink bug eggs covered in silk… We are both hoping you can help us decipher this mystery…

In my case, I am in Yelapa, state of Jalisco, in Mexico (subtropical forest), elevation approx 5 mt above sea level… On Nov. 2 I watched a stink bug (Edessa expolita) laying eggs on a fern. On November 4 I first noticed the tiny wasp parasitizing the eggs, which then covered them with some sort of silk over the course of several days. At first I thought there must be a spider nearby, but could not find any anywhere close, so I assumed it was the wasp… On November 10 a jumping spider (Theodina hespera) arrived and ravaged the whole thing.

She included these photos:


Well, I hadn’t heard of any adult wasps that spin silk either, so I wasn’t sure what to make of this. The wasp looked to me like some kind of chalcid, rather than a playgastrid, which is what I normally see hanging out on stink bug eggs. I shared some of these photos on the Hymenopterists’ Forum on Facebook to see if anyone recognized the wasp or knew of any examples of adult wasps producing silk, and several people quickly identified the wasp as a pteromalid (which is indeed a type of chalcid). No one commented on whether it could be responsible for the silk, but Rob Longair directed me to this paper, noting that adult Microstigmus, Spilomena, and others use silk in nest construction:

Melo, G.A.R. 1997. Silk glands in adult sphecid wasps (Hymenoptera, Sphecidae, Pemphredoninae). Journal of Hymenoptera Research 6: 1-9.

A quick Google image search for Microstigmus reveals that these tropical wasps produce hanging silk nests that I probably would have mistaken for spider egg sacs if I encountered them. Microstigmus and Spilomena are crabronid wasps, which have nothing to do with chalcids, but out of curiosity I obtained a scan of the paper, and I was glad I did. The introduction mentions several other adult wasps that produce silk, including two chalcids—so I tracked down the papers that were cited for these.

One of them* described something very similar to what this pteromalid was apparently doing. Signiphora coquilletti (Signiphoridae) is a hyperparasitoid, parasitizing aphelinid wasps that parasitize whitefly pupae. The females seek out parasitized whitefly pupae, insert their own eggs, and then spin webs over the pupae, not unlike the webbing in the above photos. The authors feel that the webbing most likely functions to protect the Signiphora’s offspring from further parasitism of the whitefly pupa—either by additional aphelinids or by other Signiphora females. Evidently that is the function of this pteromalid’s webbing on the stink bug eggs—and evidently it does little to protect her offspring from larger threats such as jumping spiders.

Apparently several species of eupelmids are the only other chalcids known to spin webbing as adults. Woolley and Vet note that “in these cases the webs appear to partially immobilize the host larvae, to protect the parasite eggs, and to keep the parasite eggs in the vicinity of the host larvae.” At least one of these eupelmids parasitizes gall insects, laying an egg on the inner wall of the gall near the host larva and then covering the egg with webbing—so this isn’t something you would ever see unless you were dissecting galls and examining them under a microscope.

And so it seems that Kelly and Cheryl have found something that hasn’t been documented before. If someone out there knows otherwise, please enlighten us! Below are two videos Cheryl got of the pteromalid before the spider came along.

* Woolley, J. B. and L. E. M. Vet. 1981. Postovipositional web-spinning behavior in a hyperparasite, Signiphora coquilletti Ashmead (Hymenoptera: Signiphoridae). Netherlands Journal of Zoology 31(3): 627-633.

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Mushroom-headed Mayfly

On June 19 I stopped by at the Berkshire BioBlitz at Canoe Meadows Wildlife Sanctuary in Pittsfield, MA, after spending the morning conducting a rare plant survey in Stockbridge. Whereas last time I photographed every bug I could and barely left the parking lot, this time I focused on leaf mines and galls. However, this little (~6 mm) mayfly was sitting so nice and still that I couldn’t resist taking a few photos:


My knowledge of mayflies is such that the big eyes told me this was a male, and that’s about it. When I got a side view and zoomed in to see if it was in focus, I saw that there was something weird about this one’s eyes.

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It seems to be wearing these giant red eyes as a hat, on top of some “normal” compound eyes.


It turns out these “turbinate”  eyes are characteristic of the small minnow mayflies (Baetidae), which are the largest family of mayflies in North America. The compound eyes of male mayflies are usually divided, with larger facets above and smaller facets below, but in other families the upper ones aren’t raised on unfaceted stalks like this. (In this front view you can see that there are also three simple eyes, or ocelli, the outer ones partly obscured by the antennae.)

Roger Rohrbeck tells me this mayfly is Callibaetis ferrugineus ferrugineus. For comparison, take a look at the eyes of this female baetid (Plauditus sp.)…


…and the un-mushroomy eyes of this male from another family (Heptageniidae: Stenacron).


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Sticky Plants

When you use a technical botanical manual to identify a plant, you will often encounter vague references to “glands” or “glandular hairs” on various plant parts, without any indication of the functions of these structures. Four years ago I wrote about the glands on cherry petioles that are in fact extrafloral nectaries, producing nectar to lure predatory insects so that they might hang around and prey on herbivorous insects that show up to feed on the plant. But what about those glandular hairs, which do not produce nectar? I started to pay more attention to these when my friend Eric LoPresti told me he was compiling a list of sticky plants that trap small insects.

You are probably familiar with carnivorous plants such as sundews (Drosera spp.), which catch insects with their sticky hairs and devour them.


Cerodontha dorsalis (Agromyzidae), a fly whose larvae mine grass leaves, caught by the sticky hairs of a sundew leaf.

Cerodontha dorsalis (Agromyzidae), a fly whose larvae mine grass leaves, caught by the sticky hairs of a sundew leaf.

But that’s not what I’m talking about here. All sorts of non-carnivorous plants have sticky hairs that end up covered with dead insects, producing no obvious benefit for the plant.

This spring I was looking closely at mountain laurel (Kalmia latifolia) in search of overwintered case-bearing larvae of the moth Coleophora kalmiella. I was surprised to discover that while the mature leaves of this common shrub are smooth and leathery, the newly opening ones are very sticky and regularly accumulate dead, trapped insects.


The unfortunate insects in the above photo are all platygastrid wasps, which are parasitoids of gall midges. A closer view of one of them (about 1 mm long):


Other buds had caught dark-winged fungus gnats (Sciaridae):


The insect on the underside of the bud in the above photo is something I’ve never seen before: an adult male scale insect. See the long, wispy wax filaments emanating from the tip of its abdomen? Here’s another view:


And see the little red bug at the bottom of the above photo? That’s a recently hatched scale insect nymph (“crawler”), only about 0.3 mm long.


I don’t remember now if that nymph was walking around freely or was likewise stuck to the bud. Anyway, another victim included this tiny midge (Chironomide: Orthocladiinae), about 1.4 mm long:


And here’s another dark-winged fungus gnat, this one surrounded by what seem to be phylloxerans:



So what’s with all the bugs stuck to these buds? This turns out to be a similar scheme to the extrafloral nectaries, except that instead of luring predators with nectar, the plant is offering freshly killed insects. In a series of experiments, Eric and his colleagues showed that the sticky stems of a particular columbine species actively attract insects, that these stuck insects in turn attract predators, and that the presence of these predators reduces damage to the plant by herbivorous insects. Their findings are summarized in this Discover magazine blog post, Eric’s own blog, and a paper that has been accepted to the journal Ecology. The paper includes a table that lists over 110 plant genera, in 49 families, that have sticky insect-trapping surfaces.

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Feeding on Fern Spores

Last August, I was on the way to a wetland plant plot with fellow field botanist Sally Shaw, when Sally spotted some suspicious white patches on a frond of New York fern (Thelypteris noveboracensis or Parathelypteris noveboracensis, depending on who you ask).


Flipping the frond over, I saw that these white patches were each connected with a silken gallery spun along the length of a midrib (pinna rachis).

DSC_9285 DSC_9288

This webbing was produced by moth larvae that were feeding on the fern’s spores, and the white patches on the upper surface were apparently used for disposing of frass and empty indusia (spore coverings—the yellowish things in the photos below).

IMG_5357 IMG_5354

I knew this sounded familiar, and when I got home I found the page on that discusses these moths. Stathmopoda is a genus that has been shuffled from family to family over the years, and is currently placed in Stathmopodidae, a family with 100 species worldwide* but just three in North America as far as I know. Of these three, Stathmopoda aenea and S. elyella feed on fern spores as illustrated above, and the introduced European species S. pedella feeds on alder seeds. New York fern is not a documented host for any of these (see Terry Harrison’s discussion of host plants at the above link).

I managed to catch a larva out of its silken tunnel long enough to get a decent photo of it…


…and here is one disappearing into the denser part of its webbing, which leads to the escape chamber / refuse pile on the upper surface of the frond.


Six days after I collected the frond (on August 18), the larvae turned orange, signalling that they were done feeding and ready to spin cocoons.


I gave them a nice jar of soil with a crumpled-up piece of tissue paper so they could choose whatever pupation site they liked, but this one opted to spin its cocoon just under the lid of the jar.


In early May, the first adult emerged.


IMG_3200-001 IMG_3203

This moth’s posture seems a little odd, but all stathmopodids have the habit of resting with their hind legs raised. In fact, the name Stathmopoda comes from Greek words meaning “balance” and “foot.” Pending examination of the specimen by an actual lepidopterist, I’m going to assume this is S. aenea—yet another of the many species described by Annette Braun that I’ve had the pleasure of meeting.

* Heikkilä, Maria, Marko Mutanen, Mari Kekkonen, and Lauri Kaila. 2014. Morphology reinforces proposed molecular phylogenetic affinities: a revised classification for Gelechioidea (Lepidoptera). Cladistics 30: 563–589.

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Green Islands (Part 2), and Another Mystery Moth

(Note: For those who have already read yesterday’s post, I’ve added a little more information at the end after hearing back today from Jerry Powell, who described the genus Areniscythris in 1976.)

Last January I wrote about the “green islands” that form around some galls and leaf mines when the rest of the leaf is senescing in the fall. At the end I linked to a post by Seabrooke Leckie about Ectoedemia argyropeza (Nepticulidae), an introduced moth that is now extremely common on quaking aspen (Populus tremuloides) in eastern Canada and, according to Erik van Nieukerken’s comment here, the northeastern US (I can find no published or online records of this species in the United States). Last October, I found lots of these mines in fallen leaves just down the road from my house in western Massachusetts, and I filled a sandwich box with them so I could try and raise some and get photos of adults.

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You can see that the brown blotch mines, formed between the midrib and another major vein at the base of the leaf, are much smaller than the resulting green islands.

Well, I kept the box in an unheated shed all winter, and on April 16 three little nepticulids emerged. After I photographed them, Julia managed to pin them (an impressive feat, given that the moths are about 2 mm long). Last month, we met up with Erik van Nieukerken for a weekend of leafminer hunting in Vermont, and I gave him most of the nepticulids I’d reared so he could examine them when he got back to the Netherlands. However, I didn’t bother giving him any of these aspen moths, figuring he’d seen plenty of them already.

Since then, I’ve gotten around to starting to sort through my photos from this spring. When I got to these moths, I realized they look nothing like Ectoedemia argyropeza. In fact, I wasn’t sure they even belonged to that genus.


Sure enough, when I sent Erik the above photo, he said it was clearly a Stigmella based on the lamellate scales in the collar, but he had no idea what species. DNA barcodes of larvae indicate that there are several more poplar-mining Stigmella species than are known from adults, so with any luck these moths will turn out to match one of these unknown larvae. I didn’t notice any other mines on the aspen leaves I collected, and no actual Ectoedemia adults ever emerged, so at this point I’m guessing that some, if not all, of these “green island” mines were actually made by this Stigmella species. I do see some differences between the mines I photographed and those of E. argyropeza pictured on the excellent Leafminers and Plant Galls of Europe website. Whereas E. argyropeza deposits frass in two stripes along the sides of its mine, the frass in my one backlit photo is more centrally deposited.


It also may be significant that the green “island” is so much smaller in that example, barely extending beyond the mine itself.


There is also the fact that E. argyropeza larvae are said to be mostly active at night, hiding in the petiole (where the mine originates) during the day. The larva in the photos above was feeding in broad daylight, and I can see no evidence that its mine begins in the petiole.

Although most Stigmella species make long, linear mines, the larva in this rather similar little mine I found on a willow (Salix pentandra) leaf in South Dakota turned out to be a Stigmella.


That is, Erik got a DNA barcode from the larva and it clearly fell within the genus Stigmella, but didn’t match any known species. Its closest relative seems to be another unidentified species Erik collected from willow in England. Since willow and aspen are in the same family (Salicaceae), it could be that my local aspen miner is related to the South Dakota willow miner. We shall see… needless to say, I will soon be taking another trip down the road to look for more of these mines, and will look at them more closely this time.

If you are interested in reading more about this “green island” phenomenon, here is a new paper investigating it in Phyllonorycter (Gracillariidae) and a number of other leaf-mining moths.

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Dune-burrowing Moths

In late July of 2008, Noah and I were on our way to Zion National Park in Utah when we spotted a sign for Coral Pink Sand Dunes State Park, which we had never heard of. It sounded like a good place to look for insect tracks, so we took a little detour to check it out. The dunes yielded all sorts of interesting things, including the darkling beetle on the front cover of Tracks & Sign of Insects; burrows of the endemic Coral Pink Sand Dunes tiger beetle (pictured on p. 484; I spent several minutes watching that particular larva flipping those sand pellets out of its burrow); the “sand treader” cricket whose tracks are shown on p. 505 (and whose exact identity remains a bit of a mystery); and the toothed dune grasshoppers whose tracks are shown on pp. 519 and 523—the latter being our proposed solution to Olaus Murie’s mysterious “elfin deer” tracks that appear in the Peterson guide to animal tracks. We also spent some time—as we did all across the US—excavating mole-like burrows just under the sand surface to try and figure out who was making them. The burrow of one darkling beetle larva (Tenebrionidae) is shown on p. 492; here is another, along with its inhabitant:


Here’s another, which like the one above has been filed in the “unidentified tenebrionid larvae” section on for the past seven years:

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Today, however, the author of  this blog commented on my photo of this second larva that he thinks it is actually the larva of a moth in the genus Areniscythris (Scythrididae). I am familiar with that genus, having identified the first example on BugGuide earlier this year. I thought this ID was unlikely, in part because Areniscythris is only known from dunes along the Pacific Coast, and also because larvae of that genus live in silken tunnels, and there was no silk when I excavated this burrow—at least, I don’t remember any, and there is no evidence of any in my photos. However, there is an uncanny likeness, and when I compare the side view below with the one in the original description of the genus*, I can just make out prolegs on all the abdominal segments where there should be prolegs (without looking closely, I would have thought they were just pale sand grains).


Certainly, there are rear prolegs visible in this last photo, which seems to confirm that it is a moth larva:


As far as I know, there is no known moth anywhere near Utah that is similar in appearance and habits to Areniscythris. This is certainly worth investigating, if anyone is in the area and is so inclined.

And speaking of micro-moth larvae in the western US that need further investigation, now would be a good time to look for the currant leaf-mining Acanthopteroctetes larvae I discussed here. I found them in a few different locations in Oregon, and Dave Wagner tells me he used to see them all the time in California but had mistaken them for sawfly larvae (as I had too, initially). Julia and I also found them to be extremely common in Colorado this summer, but unfortunately we weren’t able to rear any. So whereas the mystery dune-burrowing larva may have a very limited range, and should be looked for in the Coral Pink Dunes specifically, the mystery currant miner apparently occurs over much of the area from the Rockies to the Pacific coast.

Edit, 10/13/2015: I wrote to Jerry Powell about this, and he responded that he and Jean-François Landry have actually collected samples of what they are calling Areniscythris from inland dune systems as far east as Alberta, but they haven’t yet gotten around to publishing descriptions of these species. He would expect any large dune system throughout the West to harbor a colony. He pointed me to the recently described A. whitesands Metzler & Lightfoot from White Sands National Monument in New Mexico (where Noah and I also did some insect tracking), which is treated in this paper** (which happens to be in the issue of the Journal of the Lepidopterists’ Society that includes my first moth-related paper). He also noted, “If the larva you found had constructed a burrow in hard packed sand, I expect it was not closely related — I think there are acrolophids, pyraloids etc. living that way on dunes.” I presume larvae in these other groups would look substantially different, but maybe not.

* Powell, Jerry A. 1976. A remarkable new genus of brachypterous moth from coastal sand dunes in California (Lepidoptera: Gelechioidea, Scythrididae). Annals of the Entomological Society of America 69(2):325-339.

** Metzler, Eric H. and David C. Lightfoot. 2014. The Lepidoptera of White Sands National Monument 7: a new species of the genus Areniscythris (Scythrididae), a recently discovered iconic species from the Monument. Journal of the Lepidopterists’ Society 68(3):185-190.

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