Trap Nest: Part Three
An examination of the open trap nest revealed four occupied cells and one empty cell, a vestibular space between the nest plug and the occupied cells. Three of the occupied cells contained potter wasp larvae, the fourth, the one closest to the entrance, did not. It held, apparently, the remains of the original provisioning, as if the potter wasp egg never hatched. Placing the nest and this suspect cell under the microscope, I discovered two tiny wasps (both dead), three tiny cocoons (one still full), and a bunch of mummified caterpillars. Something had obviously gone wrong in this cell.
Trap nest cell contents
The cell in question, being the closest to the entrance, was the last to be provisioned. It appears, bad luck for the provisioning wasp, that one of the caterpillars captured and placed in the cell must have been secreting a number of parasitoid wasp larvae. Like the clever Greeks in the Illiad, these wasp larvae emerged from their caterpillar host (the substitute for the Trojan Horse in this metaphor) at some point after being sealed into the cell. Unlike the successful Greeks, these stowaways perished. Not having the mandibles or the mud-dissolving spit required to breach the mud partitions, they died, immured in the dark. In describing this, I feel other literary echoes, namely the horror story The Cask of Amontillado by Edgar Allan Poe. Of course the fate of the caterpillars in this cell is hardly more disturbing than the fate of the other caterpillars stung into paralysis, then devoured alive.
These wasps really were small, just a couple millimeters in length, no larger than an Argentine Ant, that common pillager of kitchen sugar. The wing venation indicated the wasps were of the family Braconidae, a large family of parasitoids with more than 1,700 species in North America. Interestingly enough, some braconids have been used as biological agents in the control of agricultural pests, pests such as the Cabbage Butterfly. Many species are colored black and red or black and orange. Since βρακον is Greek for breeches (or pants in a less stilted dictionary) I wonder if the brightly colored hind legs resulted in the family name or if it’s those swollen thighs, the coxa, that gives the family its name? As far as I could determine, these particular wasps belong to the family Agathidinae, though in consulting a recent key to the Agathindinae I couldn’t make it past the first binomial because my microscope isn’t powerful enough to examine the shape of the foreclaws, so I don’t even have a guess at the species.
While the Braconidae are interesting in their own right, this failed cell also provided an opportunity to look over the provisions. Seven small green caterpillars, all probably of the same species (no prolegs on A3, patterned prothoracic shield) were preserved. According to both Cooper and Krombein, Ancistrocerus antilope (the likely provisioner of this nest), stuffs its nest full of small caterpillars, most often the tiny larvae of micro moths—the crambid moths, the twirler moths, the concealer moths—and that appears to be the case here. My best guess, after an hour browsing bugguide, would be a Tortricid moth larvae (Tortricidae, tribe Archipini; possibly Choristoneura sp. which seemed to have a very similar prothoracic shield). The cell also contained a different species of caterpillar, 2 to 3 times as large as the others (prolegs on A3-A6, no prothoracic shield). It seems likely that this caterpillar hosted the wasps.
Krombein also reported that Ancistrocerus antilope provisioned its cells, on average, with 3 to 10 larvae, usually of a single species, and usually of early instars, the selection of early instars no doubt lowering the likelihood of interring a larvae containing parasitoids. And Krombein, out of thousands of trap nests examined, reported braconids in just two! I feel fortunate to have happened upon this complication so early in my trap nesting career.
The nest, reassembled, has been overwintering on a frosty window sill in my cold, corner office, sitting alongside plastic cups with dragonfly nymphs, other containers filled with Lepidoptera cocoons, and several heaps of gathered plant galls. It’s a nice place to sit on a cold winter day, one large creature among numerous little creatures, all of us biding our time, preparing for warmer weather.
If I hadn’t set out this trap, I wouldn’t have learned of these wasps, or known about their presence in our back yard. I wonder, often, about how few people know or care about these small happenings. I worry, just as often, about my own lack of understanding, the little I really know about the complexities of even my backyard, let alone the larger world. And I suspect, more and more, that it’s simply a failing of patience and of imagination if, for instance, a certain moth caterpillar runs rampant in our gardens and we reach for insecticides, not trusting the unseen checks to their population provided by wasps and other predators.
I think the tension, here, is between what we manage and what we don’t manage. What escapes our hand widens and grows wild. This is not pristine wild, but salvaged wild, the wild that creeps back over the land, resettling the unweeded margins, homesteading the fallow flower pots, mining the messy understory and the fetid margins of the compost. When I see weeds I see hope; and when I see unmown, unsprayed lawns I see progress being made.
Cooper, K.W. 1953. Biology of eumenine wasps. I. the ecology, predation and competition of Ancistrocerus antilope (Panzer). Trans. Am. Ent. Soc.79: 13-35.
Evans, H. E. 1963. Wasp Farm. New York: Natural History Press, Doubleday.
Krombein, K.V. 1967. Trap-nesting wasps and bees: life histories, nests, and associates. Smithsonian Press, Washington D.C. vi + 570 pp.