Baby Bagworms

Here’s something you don’t see every day:

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Well, it’s possible that you see the main object in this photo pretty regularly; it’s the portable case of the bagworm Psyche casta (Psychidae), a European species that appeared in Boston in 1931 and has since spread through much of northeastern North America.  The larvae are like terrestrial caddisflies, carrying their cases around with them throughout their lives, and when they are ready to pupate they attach their cases to various substrates.  I often find them on the sides of houses.

Adult female bagworms are wingless and never leave their cases.  The males find them and mate with them, and the females lay their eggs inside their bags and then die there.  When the eggs hatch, the larvae construct tiny cases from bits of their mother’s case, and then disperse.  That’s what all the little projections on the case in the above photo are.

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Years ago, before I knew anything about bagworms, I collected a Psyche casta case to find out what it would turn into, and all I got was a bunch of these tiny versions of the same thing.  If I had collected the case of a male, I would have gotten this:

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About Charley Eiseman

I am a freelance naturalist, endlessly fascinated by the interconnections of all the living and nonliving things around me. I am the lead author of Tracks & Sign of Insects and Other Invertebrates (Stackpole Books, 2010), and continue to collect photographs and information on this subject. These days I am especially drawn to galls, leaf mines, and other plant-insect interactions.
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4 Responses to Baby Bagworms

  1. Great! I ‘knew’ the natural history, but I’d never seen those little guys!

  2. Excellent to know this; I often find these on our split rail fence (I’m assuming it is same or similar species…)

  3. Lisa Rainsong says:

    This is fascinating – thanks!

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