The Urban Pantheist

A tiny caterpillar cuts lengths of grass stems and binds them with silk into a tube. At the insect's scale it is like a suit of armor made of bamboo. It protects the caterpillars from predators, like wasps and spiders. Look close--it's protecting a small spider from my gaze as well.


The spider abandons its hiding place, leaving the bagworm in place. This moth caterpillar is almost certainly
Psyche casta*, a European species first noticed in North America in where else but Boston, in 1931.



* The beautiful Greek word "Psyche" has a double meaning of both "the mind/soul" and "butterfly." In this case, the construction of the binomial comes to mean "moth who builds a fort."

These bagworm cases are all over the place--stuck to the exterior walls, on the window screens, and this one is on a snow shovel (which is still in the yard because...you know). I feel pretty good that this bagworm is Psyche casta

This is one of those things I've seen most of my life and never really wondered what it was. It took a little creative googling, but I'm fairly certain this is a case made by a caterpillar called Psyche casta, a little moth in the group called the bagworms. My eastern caterpillar guide and my garden insects guide both skipped this species, despite that it appears to be very common, and has an interesting life cycle. At least I think it does--there isn't a lot of information out there.

Presuming that it has a life cycle similar to related caterpillars, it constructs a case from plant material and silk. Psyche casta uses grass stems, which when dried and adhered together look like a tiny bundle of sticks. The caterpillar wanders about carrying this thing like a hermit crab, (or more like some kind of terrestrial caddis fly)eating vegetation. I think it is strange that I have never seen the caterpillar in this stage--there are lots of pictures online of bagworms poking their heads out of their refuges, but I've never encountered one. I think one of the reasons I've always ignored these things was that I didn't think there was an animal inside each one.

The caterpillar pupates inside the case, and if it is a male, it flies away. If it is a female, it doesn't grow wings, but stays inside the protection of the case. After mating, she keeps her eggs inside her body, where they will stay in relative safety for the winter. At some point, the female dies--is it before the winter or during? or is it not until her offspring hatch, and eat her body as their first meal? I haven't been able to determine it.

If you know more than I do (or know that any of what I have said above is wrong) please let me know.