Campoplegines, Part 3

I’ll conclude Campopleginae Week with this cocoon I found on a spicebush (Lindera benzoin) leaf in September:

The host plant and the big fake eyes on the caterpillar skin identify the ichneumon’s host as  a spicebush swallowtail (Papilionidae: Papilio troilus).

The 1979 Catalog of Hymenoptera doesn’t list any swallowtails (Papilio) as hosts for campoplegine ichneumonids.  I find only two ichneumonid genera that have been reared from swallowtails: Trogus (Ichneumoninae), which emerges from chrysalises, and Meochorus, which is a hyperparasitoid (i.e., parasitizing another wasp, possibly a braconid, that parasitized a swallowtail caterpillar).  Since this cocoon was already empty, I’ll have to look for one earlier in the season and collect it to find out what campoplegine is responsible. The plainness of the cocoon narrows down the options, and Bob Carlson said the dimensions of the cocoon “might help to discern whether it was made by something like Hyposoter versus something like Dusona.“

So, to review, the defense strategies in campoplegine cocoons include being dangled from a thread, making them harder to get at; having the ability to jump around, possibly thereby avoiding predators; bearing a resemblance to bird droppings, thereby looking less like a meal; wearing the host caterpillar’s skin as a protective covering; spinning a false cocoon on the outside of the host caterpillar, making it look like the caterpillar has been abandoned; and in this case, choosing a host caterpillar whose skin both resembles a bird dropping and has scary fake eyes.  This last strategy is reminiscent of that of the braconid wasp Dinocampus coccinellae, which spins its cocoon under its ladybug host, taking advantage of its warning coloration.

Now, if I just devote one week to each subfamily of ichneumon wasps, I could have them all covered by the end of August!  Or I could cover one of the described North American ichneumonid species each day for the next 14 years… another 8 years or so for the ones that don’t have names yet.  With this kind of diversity in parasitoids, you can see why it has taken me 84 posts to even mention a butterfly.

An older, and apparently unparasitized, spicebush swallowtail caterpillar.

Campoplegines, Part 2

Last August I spotted a cocoon I didn’t recognize, nestled among some boneset (Eupatorium perfoliatum) flowers:

Before I get to that, I should mention that this photo also shows the stripey legs of a crab spider (Thomisidae), waiting to grab some insect that comes to visit the boneset flowers–something like this one:

Crab spider (Thomisidae: Mecaphesa).

…And, directly behind the cocoon is this wedge-shaped beetle (Ripiphoridae):

Wedge-shaped beetle (Ripiphoridae: Macrosiagon limbata).

Macrosiagon limbata belongs to the subfamily Ripiphorinae, which, as I mentioned in this post, is composed of species whose larvae wait on flowers to climb aboard bees and wasps in order to ride them back to their nests and parasitize their larvae.  Females lay eggs among flowers, but this one is a male, as evidenced by his fancy antennae.

Anyway, I collected the cocoon, and a week later this wasp emerged:

Bob Carlson identified it as a Hyposoter species (Ichneumonidae: Campopleginae).  I took another look at the cocoon, and saw that rather than being plain white, as was my initial impression, it has a white central band and is otherwise a pale brown, which is a pattern I’ve seen on other campoplegine cocoons.  I also realized that the odd texture of this cocoon is the result of its having the skin of the parasitized caterpillar draped over it.  Both the cocoon pattern and the condition of the caterpillar distinguish this from the work of a braconid wasp larva, which would have a truly plain cocoon and would typically not devour the caterpillar so thoroughly.

The only other Hyposoter specimen on BugGuide.net emerged from this cocoon (note the caterpillar remains nearby), which is boldly patterned like the one in my last post. Evidently this genus produces a variety of cocoons, which makes sense given Bob Carlson’s comment in the 1979 Catalog of Hymenoptera:

It seems to me that Hyposoter, as presently defined, includes as bewildering a diversity of forms as any genus in the family. It would appear that the task of breaking the genus into smaller ones that are more meaningful phyletically will require a great deal of research that is not likely to be accomplished soon.

For further evidence of the diverse habits of this genus, see the comment Bob left on this website:

I wonder what Darwin might have said about the false cocoons that are spun by a few species [of] Ichneumonidae of the genus Hyposoter. These species spin their real cocoons inside the skins of hairy caterpillars, and the cocoon keeps the skin of the caterpillar firmly inflated. On the outside of the skin, the Hyposoter larva spins a small false cocoon that is quite similar in appearance to the cocoons of braconid wasps of the genus Cotesia. The false cocoon is left open at one end, and resembles a Cotesia cocoon from which the Cotesia adult has already emerged. The empty false cocoon is presumed to be a mechanism that helps to protect the Hyposoter individual in the real cocoon from being attacked by hyperparasitic wasps.

Here is an example of what open Cotesia cocoons on a hairy caterpillar would look like, but the Hyposoter‘s false cocoon would be solitary.

As for whose skin that is draped over the cocoon I found, I checked the HOSTS database and found that very few caterpillars are recorded as feeding on boneset.  The most plausible of these seemed to be Schinia trifascia (the three-lined flower moth; Noctuidae), given that caterpillars of this species feed on flowers, and that I found an adult nearby.

However, it seems that no Hyposoter is known to parasitize a Schinia, and when I suggested this possibility to Bob, he replied: “My mind’s eye is suggesting that this may be Hyposoter synchlorae, which has been reared from Synchlora aerata, which, in turn, is known to feed on flowers of Eupatorium.”  The link he referenced shows Synchlora aerata feeding on Eupatorium rugosum, white snakeroot, which is now Ageratina altissima, but Synchlora caterpillars feed on a wide variety of flowers in the aster family, so this does seem plausible.  If that’s who it was, evidently the caterpillar’s costume of flower pieces fell off by the time I found its remains.

Campoplegines, Part 1

I have been a fan of the cocoons of ichneumon wasps in the subfamily Campopleginae ever since I saw my first one five years ago, stuck to a chain-link fence along the Winooski River in Burlington, Vermont. They come in a variety of shapes and patterns, and to me they look like tiny Easter eggs (some say the white splotches that are common on these cocoons are meant to mimic bird droppings). Some dangle from threads, and some are able to jump around like Mexican jumping beans. The type I most commonly see is attached to pine and hemlock twigs or needles, so presumably the larva that makes it is a parasitoid of some caterpillar that feeds on conifers.

Cocoon of a campoplegine ichneumonid attached to a white pine needle. (5 mm)

I collected the above cocoon last January, thinking maybe I could start to learn to identify the different genera of campoplegines by the cocoons they make.  In April, an adult ichneumon emerged:

Unfortunately, it was dead when I found it, but at least I had a specimen I could get identified… except when I posted photos of it to BugGuide.net, Bob Carlson informed me that this was a species of Bathythrix, belonging to another subfamily (Cryptinae, which also includes the wingless Gelis that emerged from a spider egg sac I collected): it had parasitized the campoplegine parasitoid that had made the cocoon. Bob did suggest that B. triangularis has been recorded as parasitizing Phobocampe geometrae, and that this cocoon could have been made by P. geometrae.  Checking the 1979 Catalog of Hymenoptera (for which Bob was the author of the Ichneumonidae section), I see that B. triangularis is not host-specific but has been recorded from another campoplegine (Hyposoter sp.), two braconids (which are also caterpillar parasitoids), and Diprion similis (Diprionidae), the introduced pine sawfly.  So perhaps it is specific to Hymenoptera that have exposed cocoons, as these all do–that would make sense if females oviposit after the cocoons are formed.  It’s also possible that they oviposit in caterpillars in which they detect a parasitoid wasp larva.  If so, it might be that the sawfly record involved a sawfly larva (which is caterpillarlike) that had already been parasitized  by another ichneumonid. I’m not sure how one would determine whether a wasp emerging from a sawfly cocoon had parasitized the sawfly larva or another wasp that had parasitized the sawfly larva.  Ah, but there’s a note in the 1979 Catalog under Bathythrix that “Members of this genus oviposit into cocoons of various insects, often those of Braconidae or other Ichneumonidae,” so my first thought was right (though it still seems possible that when ovipositing in sawfly cocoons the females are really going after sawfly parasitoids).

As for the identity of the parasitized caterpillar:  Taking Bob Carlson’s suggestion that the cocoon belonged to Phobocampe geometrae, it appears that this wasp is specific to geometrid moth larvae (i.e., inchworms).  A number of inchworms feed on white pine, but of these only Caripeta divisata (the gray spruce looper) has been recorded as a host for P. geometrae.  This species feeds on hemlock too, so it could well be the host for the wasps whose cocoons I find on pine and hemlock.

Beachcombing

After four intensive days of surveying the island of Nantucket for galls and leaf mines last September, Noah and Sydne and I headed to the beach to bask and unwind.  I am mostly a forest creature, and I am ignorant of most things I see on the seashore, but after consulting some field guides (and with a correction from Ben Coulter) I can report that the birds busily scurrying around before us at the water’s edge were semipalmated sandpipers, with a few ruddy turnstones mixed in.

Semipalmated Sandpiper (Calidris pusilla)

Ruddy Turnstone (Arenaria interpres)

Well, maybe a bunch of them were sanderlings, actually–I think that’s what the ones in the last photo are.  Anyway, whatever they were, they were evidently finding lots to eat at the water’s edge, but I sat and stared right where they were feeding and could see no signs of life.  Finally, I tried blindly scooping up handfuls of sand.  More often than not, a handful of sand contained one of these:

This is a young mole crab (Hippidae: Emerita talpoida).  It’s pretty darn well camouflaged even when placed on the surface of the sand, which is not where they usually are.  I had seen these once before, three years earlier on Cape Cod.  Standing at the water’s edge, Noah had showed me these creatures (which he called “sand digglers,” and we still prefer to call them that even after learning their “real” name) that were only visible right after a wave had crashed down: in the receding water they could be seen quickly reburying themselves, digging in with their hind legs.  (They were easier to spot, being much larger–adults, I imagine–than the ones I found on Nantucket.)  For a few minutes we had been under the impression that bubbles in the sand indicated the presence of a buried mole crab, but after further investigation concluded that we could just as reliably produce one by digging where there was no bubble.  Both of these experiences with mole crabs suggest that there are lots and lots of them lurking just below the sand surface, enough to keep the sandpipers occupied indefinitely.

A mole crab disappearing into the sand on Cape Cod.

Satisfied that I had solved the mystery of what the shorebirds were feasting on, I was returning to my station on the sand, when I stumbled on another probable menu item:

This little crustacean is known as a sand flea or sandhopper, and it belongs to the order Amphipoda.  Its very similar-looking relatives in freshwater are called scuds.  I was suddenly in the middle of a big group of amphipods, bouncing around like popcorn.  And, just as suddenly, there were none.  The amphipods do higher up on the beach what the mole crabs do at the water’s edge: very quickly make themselves scarce, before the next wave of sandpipers comes sauntering by.

An amphipod disappearing into its burrow.

Ant-attracting Galls

A few months ago I mentioned that Hurricane Irene had brought down some interesting galls from the treetops, and I’m just now getting to that point in my photo sorting.  There was one spot in the woods where the freshly blown-down red oak leaves had lots of little round galls on the undersides, loosely attached to the lateral veins:

They weren’t just simple spheres; each one had a distinctive little “hat” on top:

As I sat down to inspect the ones on the leaves, I found that the ground was littered with others that had detached, with their “hats” in various stages of deterioration:

Then I saw a spine-waisted ant (Aphaenogaster sp.) come up to one of them and start gnawing on what was left of the appendage, and briefly try to drag the whole gall away.

I was suddenly reminded of elaiosomes, the nutritious little appendages that many plants’ seeds have.  These aid in seed dispersal, much in the way that having tasty berries facilitates seed dispersal in other plants, except that instead of the seeds being swallowed and passed through the gut of a bird or mammal, they are carried off by ants who will feed the elaiosomes to their larvae, then discard the seeds.  Would being carried off to an ant nest do the developing wasp larva any good?  It would probably be safe from parasitoid wasps in an ant nest.  It could also be that the gall isn’t meant to be carried off, and that this structure serves a similar function to the honeydew secretions of some other cynipid galls, attracting ants that discourage parasitoids from approaching while they are feeding. But if gall wasps can reinvent extrafloral nectaries, it seems reasonable that they could reinvent elaiosomes too.

Acrobat ants (Crematogaster cerasi) visiting an unidentified honeydew-secreting cynipid gall on scrub oak (Quercus ilicifolia).

An advantage of these elaiosome-type structures over the honeydew-secreting strategy would be that they are still attractive to ants after the galls fall off the tree, whereas (I presume) honeydew production requires that the gall be attached to the tree.  I have not been able to figure out what species causes these galls.  There is a common gall with a similar-looking structure caused by Dryocosmus deciduus, also on red (and black) oak, but those galls are smaller, skinnier, and come in clusters, erupting out of the leaf midrib:

A cluster of Dryocosmus deciduus galls erupting from the midrib of a red oak leaf, alongside one of the mystery galls and a leafhopper (Cicadellidae: Scaphoideus).

As the name suggests, Dryocosmus deciduus galls are also deciduous, dropping off the leaf before the leaf falls from the tree.  I don’t know if anyone has previously suggested that the  little nubbins on these galls function like elaiosomes.  The only thing I turned up in a Google search was this paper about a chalcid wasp that forms galls in elaiosomes.  I guess I’ll just have to keep an eye on these galls next fall and see what the ants do with them.

Oops

A few weeks ago I was cleaning out the various containers in which I had raised bugs last year, when a little speck stuck to the outside of one of the bags caught my eye.  It was a dead, 1.3-mm long beetle:

I quickly took a few photos and posted them on BugGuide.net.  I’ve noticed that the more tiny, brown, and nondescript a beetle is, the more likely it is that someone will get excited about it.  It was quickly determined that this was a “minute brown scavenger beetle” (Latridiidae), apparently in the genus Dienerella, but it seemed a little off.  Vassili Belov asked latridiid specialist Wolfgang H. Rücker to take a look, and Wolfgang suggested a couple of possibilities but said he would need to examine the specimen to be sure.  Having no further use for a tiny brown dead beetle, I put it in an empty gelatin capsule, cushioned with some tissue paper, and taped this to a piece of paper, which I slipped into a regular mailing envelope and sent off to Germany.  It occurred to me this might be slightly risky, but I wasn’t quite curious about this beetle–having no knowledge of its natural history, other than that it was apparently attracted to bags of dried plant material and insect frass–to spend more on shipping it in a parcel.  It also seemed sort of silly to send something so tiny in a big box.  Well, I learned my lesson.  This morning Wolfgang sent me a photo of what the beetle looked like on arrival (there was also a more zoomed-out view, showing the whole gel capsule smashed to bits):

A few hours later, he wrote back to tell me it seemed to be Dienerella pilifera, a species until now only known from Europe, North Africa, and Japan.  I guess a new species for the Americas would be considered a significant find.  Oops.  I will be sure to take better care of any little brown specks I find in the future.

Freshwater Jellyfish

For years, my friend Erik insisted that there were freshwater jellyfish in the reservoir near where he lives in southern Connecticut, and for years I pretended I didn’t believe they existed, even after he showed me the illustration in the Pond Life Golden Guide.  I had been down to visit a few times, and he always said you had to be there at just the right time to catch them.  So this past August when he told me the jellyfish “bloom” was happening, I decided to go down and settle this once and for all.  Unfortunately, since they don’t really exist, I wasn’t well prepared to photograph them, so in the photos below you can see the scratchy bottom of the sandwich box I used to scoop up some water, complete with some little chunks of peanut butter.

Freshwater jellyfish (Craspedacusta sowerbii), about 12 mm across.

Detail of the fringe of tentacles.

Apparently these are found in calm waters throughout the world.  A freshwater jellyfish uses its several hundred tentacles to paralyze prey and guide it into its mouth, which is in the middle and is the same opening through which it expels waste.  Those four things radiating from the center are the sex organs.  This sexually reproducing form that we recognize as a jellyfish is called a medusa, and the rest of the life cycle is spent as an asexually reproducing form called a polyp.  Polyps become encysted and dormant in the winter, and it is thought that they can be transported to new water bodies accidentally by other animals.  I still think this is all some kind of hoax though.