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?

pupa in mason jar for rearing

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.

[prob] Olethreutes albiciliana

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.

Pupal case of [prob] Olethreutes albiciliana

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.

pupa with cap sawn off by Ichneumonid parasite

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!

[prob] Ichneumon annulatorius

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.


Cattail thwacks revisited

Edit: This post was recently included in the 180th edition of Friday Ark, a weekly blog carnival focusing on animals of all sorts. You can check out the full edition at The Modulator.

Gypsy Moth egg mass

One of the downsides to learning things yourself using the internet or reference books as your guide is that it’s pretty easy to mis-identify something based on poor photographs, incomplete descriptions or information, or just vague or ambiguous wording, particularly if you have a notion about what you’re expecting. In one of the posts I did mid-January, about fungus in the woods in winter, I mentioned a large, creamy, fuzzy mass I observed on the trunk of a tree that I identified as a slime mold. Well, Jennifer over at A Passion for Nature corrected me on this by (correctly) suggesting that it looked like a gypsy moth egg mass.

Gypsy Moth egg mass

I went back yesterday to the same area and had another look at it. The particular one I photographed still looked and felt (to my frozen-numb hands) like a cattail thwack with no particular distinguishing characteristics (I didn’t want to try taking it apart because I don’t like to disturb). However, upon closer investigation, I started noticing more of these fuzzy blobs on nearby tree trunks, pretty much all within a few feet of the ground. Some of them had much more obvious visual characteristics that may have led me to the eggs conclusion if I’d seen them first. In the above and the first photo you can actually see the individual eggs wrapped up in all the little hairs that create the fuzzy mass (I think the first photo may actually be hatched eggs from last year? It’s hard to tell, but the dark spots are very pronounced). The hairs are made by the female moth as she’s laying her eggs, and are hypothesized to protect the eggs from potential rodent and avian predators by discouraging them from getting the hairs in their face and nostrils and irritating the skin.

Gypsy Moths aren’t native to North America (like a lot of common wildlife). Rather, they were brought over to Medford, Massachusetts in 1869 by French astronomer Leopold Trouvelot, who also had an interest in insects and was hoping to breed a sturdier, more productive silkworm. Well, like often happens, the moths escaped and it didn’t take them long to settle into the new landscape. They’re now found into eastern Canada as far north as Maine and the Maritimes, as far south as northern North Carolina, and currently west into mid-Wisconsin. When you consider the size of the insect in question, it’s a pretty good area to cover over that period.

Gypsy Moth pupa case

The moth’s dispersal is also made more interesting by the fact that the female moth, the recognizable white Gypsy Moth, can’t fly. When she emerges from her pupa she’s full of eggs and way too heavy to get airborne. Male moths (which are brown) can fly, and will travel long distances to reach a female, which they detect using the broad, fluffy antennae that only males possess. These antennae are specially designed to pick up the pheromone molecules released by the female when she emerges. Near a couple of the egg masses I found pupa cases left from the female when she emerged. The cases also have hair tufts that presumably protect them the same way the hairs in the egg mass do.

Gypsy Moth egg mass and pupa case

Still, if the females aren’t moving, then the eggs are going to be laid near where the female emerges, which also doesn’t help much with dispersal. Instead, dispersal is carried out by the caterpillars (weird, eh? The only ones without wings). Caterpillars, during the course of their feeding, climb to the top of the tree and then spin a line of silk which they use to “balloon” on the wind over to the next tree. I can’t imagine this taking them very far, so it would be a very slow dispersal.

Gypsy Moth laying egg mass

This photo (used with permission) is of a female caught in the act of laying an egg mass in late summer. She was found inside a porta-potty, so I can’t imagine the caterpillars would have much to eat when they hatch, but I gather Gypsy Moth females aren’t too particular about where they lay their eggs. The larvae will feed on up to 500 different species of trees, but particularly favour oak. Most of the egg masses I came across were on rough-barked tree species, primarily Black Cherry. Caterpillars hatch from their eggs in early spring, late April into early May. They feed on tree leaves and can be a severe pest in some areas where they completely denude trees of their foliage, particularly since a single egg mass can contain up to 500-1000 eggs. In late June to early July they begin to pupate, and emerge as adult moths after a couple of weeks. Females lay egg masses shortly after emerging, and adults will never eat. Adults die shortly after mating, and the species overwinters in the form of these egg masses.

It’s funny how once you know to look for something, it suddenly seems to jump out at you everywhere. Now that I’m aware of these and what they are, I’ll be keeping my eyes open for them on future walks.