Acorn Weevils

It’s another mast year for red oak (Quercus rubra) in my neck of the woods, which means that for the past couple of weeks, large nuts have been raining down from the treetops, making it a little treacherous to go for a walk in the forest. Last November, once the acorns had all fallen, Julia and I collected a few gallons of them to process and use for food. (We’ve made tasty acorn bread and acorn cake, but so far our favorite is acorn falafel.)

Anyone who has collected acorns is familiar with the whitish grubs that turn the insides to dust, eventually exiting through round holes like this one:


The grubs are immature weevils in the genus Curculio (Curculionidae).

After collecting our acorns, we dried them by placing them on trays by the wood stove, and I think this arrested the development of most of the larvae that were feeding inside them. However, on December 7 I noticed two mature larvae squirming around on one of the trays.


Just for the heck of it, I dropped both larvae into a jar of soil, and after they burrowed down I put them in the little refrigerator in the basement where all my other bugs pass the winter. I took the jar out on March 1 along with everything else, but it wasn’t until June 14 that an adult finally appeared.


When I was satisfied with the photos I’d taken of it indoors, I brought it out to a red oak sapling in the yard to try for some more natural shots.


It soon wandered onto a young stem, and as I continued to photograph it I realized that it was feeding by chewing a tiny hole into the stem.


In the last photo above, it has finished feeding and the hole is visible just to the left of the tip of its proboscis.

Added 10/25/16: Here’s a great video Laura and David Hughes got last year of a larva chewing its way out of an acorn. Amazing to see it squeeze its blobby body through a hole that is just barely big enough to fit its head capsule.

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People regularly send me photos of mystery objects and other bug-related phenomena to see if I recognize them. Often I’m able to respond with a precise (or approximate) identification, and that’s the end of it. Other times I’m intrigued by the mystery but don’t have anything too useful to say about it. My last post featured an unusual case where I was able to collect the larva in question and raise it to an adult. More typically when a mystery piques my interest, I offer to post the mystery photo on my blog to see if any of my readers recognize it. Lately, a pattern has developed where the photographer says sure, go ahead and post it, but then I never quite get around to it… until now! Tonight I’m going through my old emails and rescuing these photos from the depths of my inbox. [Note: It seems that there is nothing I can do to convince WordPress to make proper spacing between the blockquotes and images. It all looks very nice while I’m editing it, but it’s all messed up when I preview/publish it. Sorry about that.]

First up is a pupa found by Scott Smyers on Mount Wachusett in eastern Massachusetts on July 11:

I found this interesting pupa under a snake board in a field at Wachusett on Monday.  I looked through your book and couldn’t find anything like it.  Any ideas?


It’s definitely a lepidopteran pupa, but I don’t remember ever seeing one with bold longitudinal stripes like this. [Edit: Vazrick Nazari recognized it right away as the chrysalis of a common wood nymph, which is a butterfly I know well. That’s one mystery down!]

This next one was sent to me by Erin Banks Rusby around the same time (July 13):

I work for a non-profit in the Palo Alto, CA area and saw the following on a plant in Menlo Park, CA. I can’t tell you what plant it was on, unfortunately, but I can tell you that there were other markings like this one on other leaves of the plant. Is it an insect or bug that made it and do you have any idea what it could have been?

My response at the time was:

Interesting pattern!  It’s not immediately recognizable to me… it appears to be something on the leaf surface, but I can’t quite tell from the photo whether it’s something clear and shiny or something white and fuzzy.  If the former, all I can think of is some kind of slug/snail, but that seems unlikely given how convoluted the pattern is.  If the latter, I’ve seen planthopper nymphs and related insects (e.g. psyllids) leave behind something vaguely similar, but again, not such an intricate pattern.  I’d be interested to hear more details or see other examples.

She consulted with her organization’s botanist/naturalist, who suggested it was a leaf mine of some sort. If it were a mine, it would pretty much have to be from a moth in the family Gracillariidae, since very shallow mines resembling snail trails are characteristic of that family.  But it would be very unusual for a gracillariid mine to be so tightly contorted, and there are a few outlying dots in the periphery of this pattern that make me think it is in fact some kind of whitish substance that has been deposited on the leaf surface. Unfortunately we don’t know what the host plant is, but maybe someone will recognize it from the photo above.

The next one was sent to me a year ago (October 14, 2015) by Piet Tutelaers:
Since 2011 our insect working group of the KNNV Eindhoven in The Netherlands is puzzled with these strange cocoons. We have asked help from people from EIS (European Invertebrate Survey) in Leiden also in The Netherlands. They thought it would probably be cocoons from Asterodiaspis variolosa (Ratzeburg) [the golden oak scale; family Asterolecaniidae] but that turned out to be false. We have tried to breed the cocoons to see what animal comes out but that has failed so far (see photo 1
and photo 2).

The left cocoon in photo 1 and the one in photo 2 is the unknown one and the smaller right cocoon in photo 1 is from Asterodiaspis variolosa . The cocoons are 4mm long and 1.5-2mm wide. The small white cover is the place where the cocoon is opened and left by the inhabitant.

…The cocoons can be found in forests (plantations) of Douglas fir, a fir that is not native to Europe but is cultivated for its wood. Here we find the cocoons underneath fallen dead branches in the neighbourhood of Douglas fir. There should be some free air between the place of the cocoon and the soil.

I have opened one cocoon in order to see what is inside it and have made a photo with my stereo microscope. This photo gives me the strong impression that we have to do with an insect (see attached photo).

Because the Douglas fir is native in your country this insect is possibly known in the USA? So I hope you can help me in solving this puzzle.


My response:

Looking at the first two photos, I was going to guess an egg sac of a spider such as Agroeca, but your photo of the opened one makes it clear that it is a cocoon, presumably of a moth.  Would it be possible to remove the object (pupa?) from the cocoon and get clearer photos of it?  Unfortunately I have never seen something quite like this before.  It may or may not be something related to the Douglas-fir; I live on the other side of the country from where Douglas-fir is native, and have only spent a little time exploring the Pacific Northwest.
Piet was going to try and get sharper photos of the pupa, but never got back to me with those, which is my excuse for taking so long to get around to posting these photos. (It occurs to me now to wonder if the object inside is an embryo rather than a pupa—it sort of reminds me of the egg coverings made by certain ground beetles, but I don’t know if any of them are capable of making a silken lid like this.)
I have no such excuse for not doing anything until now with the photos below that John van der Linden sent me in August 2015. Julia and I had met John a few weeks earlier when we stayed with MJ Hatfield in northeastern Iowa, but John’s photos are of things he found on tree trunks in India.
1. The top image shows a flattened case that has a two-lobed shape. This case was structured like a turtle shell. The visible part is larger in diameter and faces out (the “carapace”). The invisible part is smaller in diameter and touches the bark surface (the “plastron”). The larva hid sandwiched between these two layers.
This well-camouflaged object is shown in the inset and in the upper left corner of the larger photo. I asked John if it was a portable case, and he replied that from what he recalled, both it and the next one were very loosely attached to bark with just a few strands of silk “…as if the larvae were camping out for a while…but could also sever the strands and move if they wanted?”
2. What I called the “cobra case” because it reminded me for some reason of the hood of a cobra. Fascinating architecture (see diagram, next picture). Yes, the case actually had two rows of holes built into it, along its margins!!
3. Diagram of the cobra case.
4. Cobra case stripped down to just the tube part of the case, with larva partly emerged.

cobra-case-larva-45. Another view of the cobra case larva. The head was distinctly flattened into a blunt disc with the approximate inner diameter of the tube part of the case, so that when the larva rested inside the tube its flattened head acted just like a manhole cover, sealing off the tube.

My comment on the “cobra case” was:

The larva looks like something gelechioid to me, like a Coleophora… somehow the construction of the case is reminding me of Batrachedridae, which includes the octagonal casebearer as well as a species (pictured in my book) that makes a vaguely similar expanding frass shelter on palmetto leaves [here is an example on BugGuide; both of these moths are now placed in the family Pterolonchidae].

As a bonus, I’ll leave you with a mystery that got solved before I got around to posting it here. On June 17 of this year, Valerie Bugh wrote:

I have just found a second example of a mystery I can’t solve. I found the first about 5 years ago in FL. The second was found today in Austin, TX. Size is just under 10 mm if I remember correctly. They seem sort of waxy, and the “tail” is oriented down. I thought about some sort of diptera puparium, or maybe a wasp or bee nest. Anyway, I was wondering if you’ve seen this and know what it is.


My response:

The shape reminds me of some spider egg sacs, but the material doesn’t seem to make sense for that… The closest thing I can think of is a resin bee nest, but the ones I’ve seen always are packed with pebbles and never have any kind of tail like that. . . I would strongly suggest that you put it in a container and give it a few months to see if something comes out, and if not, then cut it open to see if you can make sense of its contents.

In August Valerie wrote back with an update. The insect turned out to be one she knew as an adult—see her photo here.

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A Hidden Masterpiece

Last December, Jennifer Kleinrichert sent me this photo of a polka-dotted larva (prepupa) surrounded by an elaborate silken structure, wondering if I knew what it was:


My response:

I’m afraid I don’t know this one… I’ve seen a photo of something similar once before; see the third one on this page. It would be interesting to know if this larva ends up spinning a similar dense, white cocoon. The polka-dots on your larva remind me a little bit of some pyraloid moths… can you tell me anything else about the context?  Looks like it was under a plywood board?  If you don’t mind, I’d love to post this as a mystery on my blog.

She replied that she and her husband had been changing some pictures in a bulletin board, and upon opening the door found the larva in between the two frames. In the photo below, the larva’s creation is visible on the horizontal board directly below the photo of a viceroy.


I decided to hold off on posting the mystery here, because in January Julia and I happened to be visiting her parents in Ohio, just a half-hour drive from the bulletin board, and I figured I might as well take a crack at raising the larva to an adult. Jennifer and her husband Steve met us at the bulletin board and removed the panel for us. The larva was still in the same position within its gauzy double fence, which was about 6 cm across.


We gently removed the larva and put it in a sandwich box with a  folded-up paper towel.


I kept it in the refrigerator until March 1. After that, I took a peek at it every day, and although I didn’t actually see it move much, it seemed to be in a different position every time I looked. I expected it to pupate soon after it was exposed to warmer temperatures, but it wasn’t until nearly two months later, on April 23, when I found the larva suspended in some webbing in a fold of the paper towel where I hadn’t seen it venture before.


Another week passed, and finally, on May 1, it shed its skin and pupated.


I didn’t want to disturb it too much then, but I was able to get a better shot of the larval and pupal exuviae on May 27, when the adult moth at last emerged.

My guess that it was some sort of pyraloid moth turned out to be correct. Specifically, it was a dogbane saucrobotys (Crambidae: Saucrobotys futilalis). I don’t think I had seen an adult before (at least, I had never been moved to photograph one), but the larvae were conspicuous in the dogbane patch by our mailbox last September.
I never would have guessed that the larvae leave their messy feeding webs to spin such intricate structures for hibernating and pupating.

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Bean Borer

Last August, Julia noticed a few holes in some string beans in the garden.


One of holes had droppings pouring out of it, and we could see someone fuzzy inside.


I opened this tunnel up for a better look at its inhabitant.


A quick look in a field guide told me what this was going to turn into, and I generally focus my rearing efforts on unknowns, but I decided to make an exception. After munching on beans for another week, it shed its fuzzy skin to reveal a fuzzy brown chrysalis.


In the spring, it emerged as a gray hairstreak (Lycaenidae: Strymon melinus) as expected. It obligingly posed on a dandelion before fluttering away.


We’re more than happy to sacrifice a few string beans to have these around.

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Birch Munchers, Large and Small

The woods behind our house were logged not long before we moved here, and as a result there are lots of black birch (Betula lenta) saplings around. Yesterday on my morning walk I spotted this amazing caterpillar eagerly devouring the leaves on one of these saplings:
Caterpillars of this species get to be well over 10 cm long. In the spring they emerge as cecropia moths (Saturniidae: Hyalophora cecropia), which some sources say are the largest moths in North America. Others say the black witch (Erebidae: Ascalapha odorata) is larger, which may be true for adults, but the caterpillars of that species are only up to 7 cm long. Here’s the only adult cecropia I’ve photographed, from over a decade ago:


Just a little farther down the trail, I noticed some black birch leaves containing larvae of Nepticulidae, the family that includes the smallest moths in the world. This one leaf has 14 larvae in it:


If you look closely at the above photo, you can see the bright yellow larvae at the ends of the mines. Here is a close-up of the largest mine:


I believe these are Stigmella corylifoliella or something else in the S. betulicola species group. Here is a moth I reared last year from a similar larva:


This two-millimeter moth would fit on one of the red knobs on the cecropia caterpillar’s back.

Looking at some other mined black birch leaves, I saw that not all of the Stigmella larvae were yellow. Note the nearly colorless one at the bottom of this photo:


Here’s a leaf with only the pale larvae, some of their mines nearly complete:


The pale larvae pretty consistently fill the first part of their mines with frass particles carefully placed in closely spaced, zigzagging arcs, then transition to making a narrow central frass line toward the end of the mine.


Erik van Nieukerken has determined that there are at least six different Stigmella species forming linear mines on birches in North America, and I believe this is one that doesn’t have a name yet. I reared some adults this spring, but I haven’t gotten that far in my photo sorting yet.

I saw some other leafminers and leaftiers on black birch as I continued on my walk, but I didn’t feel moved to photograph these. But then I saw this leaf, and couldn’t resist taking a closer look:


Flipping the leaf over to look at the underside, I saw what was responsible for the little whitish patches. See the elongate object near the tip of the leaf?


Here’s a closer look:


It’s the portable case of a casebearer moth (Coleophoridae: Coleophora), made from a piece cut out from a leaf. In this backlit shot, you can see the larva inside, its head right at the mouth of the case:


A casebearer feeds by attaching the mouth of its case to the underside of a leaf, chewing a hole in the lower epidermis, and mining into the leaf by extending the front of its body out from the case. Well, that’s how older larvae feed; the youngest larvae feed as regular leafminers, their bodies entirely within the mine. The mine is then cut out from the leaf to form the portable case. In the case above, you can see that the larva left the very tips of the leaf serrations unmined. The presence of leaf serrations tells us that the case was cut from the edge of a leaf—in fact, it came from the base of this very leaf.


The photo above shows the underside of the leaf, and you can see that there is something projecting from the left edge of the missing leaf piece. This is a smaller case that the larva abandoned when it mined into the leaf to create the case that it is currently wearing. And where did that case come from? I surveyed the various holes in the leaf (most of which were not made by this larva) in search of one the right size and shape. I knew I had found the right one when I saw that it, too, had a smaller abandoned case attached to it!


This one was just a millimeter long. To the right of it, you can see a tiny mine the larva made while living in this case; the entrance hole is in the lower right corner. The origin of this original case appears to be a nearby hole that is visible in this zoomed-out view (which shows several more mines made by the young larva before cutting its third case):


Five Coleophora species are known to mine birch leaves, but taking this one’s habits into account I can rule some of these out. I suspect it is C. lentella, which happens to be the only one of the five that has been reported from black birch (and its name is a reference to this host, Betula lenta). It might turn out to be C. comptoniella, though; if so, it will make yet another, much larger case after overwintering. Of the five birch feeders, I have so far only reared C. serratella:


I found another larva of the same type on another leaf of the same sapling. This one was wandering in search of a new feeding site:


I’m going to attempt to rear these, but I’ll be more likely to succeed if I can find more in the spring.

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Adapting to New Menu Options, Part 2

One of the reasons certain nonnative plants come to dominate the landscape is that they are released from the specialized insects and pathogens that keep them in check in their native range. So I’m always interested to see what insects are able to make use of these plants. I’ve often noticed little nibbles like this on Japanese barberry (Berberis thunbergii)…


…but had never actually spotted anything feeding on the leaves until one autumn day when I stopped to investigate some particularly fresh-looking nibbles. This “window feeding” (leaving one epidermis intact) turns out to be the work of early instars of an inchworm, which starts eating all the way through the leaves as it grows larger.


The above photo was taken on September 28. Here is the same caterpillar on October 2…


…and October 8:


The caterpillar burrowed into soil not long after this, emerging as an adult in March after I took its jar out of the fridge.


Its patterned wings became good camouflage when it came to rest on the fallen white pine in my yard:


This native moth is known as the barberry geometer (Geometridae: Coryphista meadii), and barberries are its only known host plants. Its original host is presumed to be American barberry (Berberis canadensis), but this plant does not occur in the Northeast. So like Stigmella rhamnicola (but even more dramatically), this moth has expanded its range because of the introduction of a nonnative plant. Sorry to say the little nibbles made by the caterpillars aren’t enough to keep the barberry from taking over places where the deer are selectively eating all the other understory plants.

Last October I discovered that barberry geometers aren’t the only caterpillars feeding on leaves of Japanese barberry. Whereas the inchworms “window feed” from the lower leaf surface, I found these two caterpillars grazing in little patches on the upper leaf surfaces:


These are the same two caterpillars a week later:


Five days later, they looked much more similar to one another:


Unfortunately I was unable to rear these to adults. I have found similar caterpillars feeding on Christmas fern (Polystichum acrostichoides) and wintergreen (Gaultheria procumbens) in the fall, so I think this is just a species that feeds on whatever is still green at the end of the year rather than any kind of barberry specialist. It’s some sort of owlet moth (Noctuidae); I had one of the wintergreen feeders emerge in June, but I haven’t figured out what it is yet and I’m nowhere near there in my photo sorting, so stay tuned…

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Moths From A Willow Leaf

Over the past few days, a break in fieldwork has given me a chance to start catching up on going through my photos from this year—I’m exactly five months behind at the moment. On March 19 I finally got to the end of a story that started with the Berkshire BioBlitz on June 19 of  the previous year. I had collected this leaf of silky willow (Salix sericea) in the hope of finding out which of the nine willow-feeding species of Phyllonorycter (Gracillariidae) was responsible for the leaf mine on it, since as far as I know there is no way to distinguish among the mines of these species (though a few can be ruled out based on geography).


In my hurry to document as many species as possible in a short time, I didn’t investigate what had made the webbing and leaf fold next  to the mine. This nearly proved disastrous, since it turned out a caterpillar was hiding in the leaf flap, and by the next day it had consumed much of the leaf. Fortunately, it didn’t eat too much of the mined portion.


I moved the caterpillar to a separate vial with fresh willow leaves. I don’t usually collect non-micro moth caterpillars to rear, but when they show up on leaves I’ve already collected I figure I might as well.


On June 28, the adult leafminer emerged, revealing itself to be Phyllonorycter salicifoliella, and leaving its pupal skin protruding from the mine.


The externally feeding caterpillar developed much more slowly, and I had to keep collecting new willow leaves to feed it. Here it is on July 6 with an old willow leaf that has gone yellow:


On July 29 it was looking pretty different:


The last photo I took of it was on August 4…


…but I noted in my journal that it turned pink and burrowed into soil on August 12. As it happens, I had tried to rear this same species eleven years earlier (from a caterpillar feeding on black cherry), so I have a photo to illustrate just how pink it was when ready to pupate:

shutesbury aug 26 009

Nothing stirred in the jar for the rest of the year. I put it in the fridge over the winter, taking it back out on March 1. Almost three weeks later, an adult confused woodgrain (Noctuidae: Morrisonia confusa) appeared in the jar. Having no further use for it, I let it out to see if it could find others of its kind. Here it is resting on a fallen white pine at the edge of my yard:


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