Caddisflies (order Trichoptera) are often mistaken for moths (Lepidoptera) because they share a number of similarities. Like some moths, caddisflies hold their wings tent-like over their abdomens when at rest. Like some moths they are often attracted to lights at night. And like some moths they have long, thread-like antennae. Closer inspection, however, reveals a few key differences. While moth wings are covered in scales like butterfly wings, the wings of caddisflies are instead covered in fine hairs (the order name “Trichoptera” is Greek for “hairy wing”).
Moths also have sucking mouthparts (proboscises) that are conspicuously coiled under their heads when at rest. They use these mouthparts to siphon nectar from flowers. Caddisflies instead have chewing mouthparts. Although most adult caddisflies don’t feed, these palpi are left over from their lives as aquatic larvae. Young caddisflies live in streams, lakes, and ponds, and most species construct cases out of available material to conceal and protect themselves. They use their chewing mouthparts to feed on detritus, although some species are predatory on other aquatic invertebrates.
Finally (and this is a bit more of a generality) moths with thread-like antennae tend to hold them outward or backward. Caddisflies, in contrast, tend to hold their antennae directly forward.
Knowledge of these few details can help anyone become an expert on distinguishing caddisflies from moths. Next time you’re gathered around a porch light marveling at all the insects you can impress your friends. Assuming you enjoy gathering around porch lights to marvel at insects. Which you should.