I was driving home from work last week and noticed
what appeared to be a moth, judging by the face, stuck on my windshield wiper.
The wings were flapping wildly in the breeze. When I got to a red light, they
didn’t look like moth wings and I could see the legs were moving. This bug was
still alive and trying to escape. I pulled over at the next chance I could so I
could free this mystery critter. I wasn’t sure what I was looking at (or how it
was still alive; half its body was smashed) until I happed upon it in a book I
was flipping through. It was a caddisfly.
What is a caddisfly? They are an order of insect
(Trichoptera) that is similar to moths and butterflies (order Lepidoptera) with
hairy heads and larval cocoons. However, the caddisfly larva lives underwater
and makes its case from material in the stream, such as small pebbles, held
together by silk that it secretes from glands. And unlike moths, the wings of a
caddisfly are not covered in fine scales (the “powder” that gets on your fingers
if touch a moth or butterfly’s wings).1
 |
| Caddisfly larva, with and without case South Dakota Game, Fish, and Parks |
 |
| Adult caddisfly Pennsylvania Fish and Game Commission |
Caddisfly larvae are a favorite meal for aquatic
critters like salmon. An entire cohort of caddisflies emerges from their
cases at once and moves toward the surface to begin a brief (two weeks)
adulthood. It becomes a veritable smorgasbord for fish. Caddisflies are also an
important indicator species. An indicator species is one that’s absence or
presence is an indicator of the general health of an ecosystem. Caddisflies are
sensitive to water pollution, so an abundant population of caddisflies is a
sign of a healthy stream.2
 |
| Caddisfly larvae, Mashel River |
1 From Insects,
Their Natural History and Diversity by Stephen A Marshall
2 From The
Northwest Coastal Explorer by Robert Steelquist
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