Hatching a pupa

Two weeks ago, the same weekend Dan walked back with me to show me the jewelwings, he pointed out what he thought was a chrysalis that he’d spotted dangling from the branch of a shrub alongside the path. (This was the primary purpose of the expedition; the jewelwings were a nice addition.) When I stooped down for a closer look, it turned out not to be a chrysalis at all, but actually the pupa of a moth that had slipped out of its silken cocoon. (Butterflies, when they pupate, form hard-shelled cases without any additional protection, while moths usually form soft-shelled pupae that they encase in a cocoon spun with silk fibres, sometimes incorporating other material such as leaves.) The fibres of the cocoon were still affixed to the branch, but now the pupa dangled delicately from one end. From rain, perhaps, or other weather effects?

I took a few photos of it in situ, and then (at Dan’s suggestion) carefully broke the branch off to bring it back to the house to try to rear it and see what was inside. I placed the twig into a large, clear mason jar, crumpling up a tissue and placing it underneath one end so that the pupa would be elevated from the floor of the jar, aware that the moth would need room to be able to stretch its wings out as they dried. I covered the top with cling wrap to keep the moth inside until I found it, poking half a dozen holes into it with the tip of a pen to allow air circulation. And then I put it on the kitchen counter and waited.

Four days later when I came home from work, Dan pointed out a moth inside the jar. But it wasn’t the moth I was expecting to be inside the jar. Not that I had any idea, really, what species was inside the cocoon, but I did know that as the pupa was about 15mm (3/4″), the moth inside it would also need to be at least that big. The moth fluttering about the jar now, scurrying over the cling wrap and around the glass walls, was just a little micro, less than a centimeter (1/2″) long. I jarred it and placed in the fridge to cool, with the intention of slowing it enough that I might be able to manage a decent photo to identify it. I eventually got one through the clear plastic of the container, but it was sufficient to pick out a probable ID: Olethreutes albiciliana, a member of the family Tortricidae for which there is several records but no detailed life history information on the web. The records I’ve found have been for Alberta, Ontario, Indiana, Massachusetts and Vermont, suggesting it’s primarily a northeastern species perhaps extending west through the Boreal. I don’t recognize the plant it was attached to, but the substrate the caterpillar pupates on isn’t necessarily the same one it was feeding on.

A closer look at the plant revealed this tiny pupal case affixed to the twig at the base of some leaves. It looks a bit like a mantis or some other bug, but the long hooked “arms” are just bits of the pupa that split along thinner creases in the shell when the moth forced its way out, probably where the pupa traced the antennae (if you look closely at the top photo you might see that the pupa clearly shows an abdomen, two sings wrapped around the front, and the antennae folded down against the body in front of the wings. It even sort of shows the eyes, though they’re harder to see). It’s funny that I hadn’t even noticed this one when I broke the twig off and brought it inside.

It was a longer wait for the original pupa to “hatch”. Finally, when I came home from work yesterday afternoon, two weeks after collecting it, the top of the shell had been neatly popped off and lay on the floor of the jar.

And running around the mouth of the jar, under the cling wrap trying to find a way out, was the adult that had emerged from it. But it wasn’t a moth at all. It was a wasp!

I chilled this guy, too, and then took a couple of photos which I posted to BugGuide. The long, narrow body and antennae identify the wasp as a member of the family Ichneumonidae, a group of wasps that parasitize the larvae of other insects, primarily lepidoptera (moths and butterflies) and beetles. The expert on BugGuide placed it in the subfamily Ichneumoninae, and I browsed through the BugGuide catalogue till I found a possible match: Ichneumon annulatorius, based on thorax and leg markings and lack of white on the antennae. This species also seems to be a northeastern species, based on the locations of specimens submitted to BugGuide for ID.

This PDF had some useful information about the group, including the species I. annulatorius. The wasps emerge and mate during the summer and fall. The females then spend the winter hidden under loose bark or sometimes moss on trees or logs. In the spring, they begin searching for a suitable lepidopteran host, either caterpillars or newly-formed pupae, and lay their eggs, fertilized using the sperm they’d stored over the winter. The wasp larva develops in the pupa and emerges a few weeks later to start the cycle again.

This individual is a male, as it lacks a long, thin ovipositor at the tip of its abdomen. After I’d got my couple of photos I let him go so he could find himself a female. Interestingly, though, the paper notes, “Specimens may also be held for months at room temperature by supplying ample water and nutrients in the form of a 50/50 honey/water mixture.” If you think of the amount of time between when a female would have emerged from her host pupa in the summer, to when she lays her eggs the following spring, they actually have a reasonably long lifespan, for an insect. Although I don’t think the males sting, lacking the ovipositor (which is the organ that stingers are modified from), it’s hard to think they’d make very good pets.