Common Bagworm
We found these little bundles of dry grass sticking to almost every available surface on May 23, 2012.
This was not unusual. We find them every year. The unusual bit is that, normally, when we find them they are stuck firmly to the surface. But this time, we found some that were still actively crawling around.
So, living in that case is a little caterpillar. This is pretty straightforward to identify; it’s a bagworm moth caterpillar, and specifically it looks to be the accidentally-introduced Common Bagworm, Psyche casta.
Just to show that not all introduced species are much of an issue, it seems that in Michigan the Common Bagworms mainly eat lichens growing on fenceposts. The case is made out of short bits of dead grass held together by silk, and has a number of functions: armor against predators, camouflage, moisture retention, and thermal insulation.
There are both female and male common bagworms. The males have wings, but the females are wingless and never really come out of their bags. It looks like they hibernate in their bags over the winter, then crawl to a good spot to pupate in the spring (which is evidently what this one was doing when Sam found it). The females lay eggs in the bags and die. When the eggs hatch out, they go ahead and look for lichens to eat.
As an introduced species with few native predators, these have gotten to be very common. But as long as crustose lichens on fenceposts are not an agricultural crop, I doubt anybody will much care about them.
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I keep finding these little bsgeifms on the outside
Of my screens and on the outside of my condo
On the painted plaster.
I keep finding these little bagworms on the
Outside of my screens and on the outside walls of
my painted plaster.