Caddisflies (order Trichoptera) resemble some moths (order Lepidoptera) that also hold their wings roof-like over their abdomens. One way to tell them apart is to look closely at their wings. Like butterflies, moths have wings that are covered in scales. Caddisflies, on the other hand, have wings that are covered in hairs. It’s also useful to look at the mouthparts. Moths have long proboscises for sucking nectar from flowers, while caddisflies have well-developed palps and reduced mandibles and feed mostly on liquids (Triplehorn and Johnson 2005).
Caddisfly adults are relatively unremarkable, but their aquatic larvae are very interesting. Many of them live inside portable cases of various shapes that are built from sand, pebbles, leaves, sticks, or silk. The particular construction used by a given caddisfly larva is often useful in identifying the genus or even species (Triplehorn and Johnson 2005).
Caddisflies have something important in common with the stoneflies, mayflies, and alderflies that I’ve covered recently. All of them are useful indicators of stream health. These insects are all sensitive, to varying degrees, to low dissolved oxygen levels and poor water quality. It’s interesting that I’ve recently found so many of these insects along a stretch of the River Raisin that is generally of poor quality. The ability of these insects to survive in this water this spring may have something to do with the excessive flooding that has occurred in the last two months.
Triplehorn, C.A. and N.F. Johnson. 2005. Borror and DeLong’s Introduction to the Study of Insects. Seventh Edition. Thomson Brooks/Cole, Belmont, CA.