Lichen Bagworm

2022 November 13

I spotted what looked like a piece of dirty lint crawling up the side of our house near the front door on October 22, 2022. It was about the size of a piece of uncooked rice, and consists of a bunch of sand and other debris bound together by silk. It looked like a lot of the debris was insect skins, probably mostly its own molted skins.

Coming in for the closer shot had spooked the inhabitant enough to make it pull inside, but after a minute or so it poked its head back out and recommenced climbing up the wall.

It had a caterpillar-type head, but looked a bit armored.

This is clearly a bagworm, which are moths in the family Psychidae. The caterpillars build armor/camouflage for themselves in the form of a bag covered in debris, which they carry around with them as a kind of shell. This particular one is a Lichen Bagworm in the genus Dahlica, and is probably Dahlica triquetrella. These are native to Europe, and back home they have both winged males, and wingless females that never come out of their case. Here in North America, at some point we acquired a number of the females that came over accidentally, but no males. So, our local specimens reproduce parthenogenically, where each generation is essentially a clone of the previous one.

As for how they got here, they arrived due to the way that they overwinter. The way their lifecycle goes, is the eggs hatch out and then find a patch of lichen to browse on and build a case from. They reportedly sometimes will eat other small insects if they catch them, but the lichen is the main thing. They keep building out the case as they grow, until fall comes around. They then climb up on some tall object, stick their case to it, and then hibernate through the winter. And if they happen to stick themselves to something that is going to move, like a stack of lumber being shipped, or the side of a ship or a cargo crate or what-have-you, then humans obligingly carry them all over the world. Once spring comes around, they pupate, lay their eggs, and die. The newly-hatched eggs then emerge, crawl off until they find a patch of lichen, and everything begins again.

We used to have a huge number of these. We would constantly find them sticking to the walls of buildings, other structures, the sides of trees, and pretty much any object of any height. But, recently we’ve been seeing a lot fewer of them. They have gone through what looks like the standard invasive-species cycle: (1) population explosion due to lack of disease and/or predators, (2) population crash due to either a local predator learning to eat them, or a new disease running through their population due to overcrowding, and (3) stabilization of the population at a level where they are just another addition to the local fauna.

Of course, these aren’t particularly attention-getting invaders. Nobody much pays attention to lichen, and since that is what they eat, the only reason anyone really sees them is because they crawl up onto walls where they are about eye-level.

This suggests that if I collect some specimens of moss and lichens, and dissect them to see what is living in there, I am likely to find things that I would otherwise never see.

3 Responses
  1. December 23, 2022

    I thought the issue with Dolly was that her DNA became frayed with age so her clone(s) started life as middle-aged sheep. Wouldn’t that happen with parthenogenically-reproducing animals?

  2. December 30, 2022

    My understanding is that when eggs are formed, there is an enzyme that re-lengthens the telomeres on the chromosomes. But when cloning, the chromosomes are being inserted into an egg that already exists, and so this telomere-lengthening doesn’t happen.

  3. January 15, 2023

    Aha! Thanks for the reply.

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