Years ago I harbored something of a low-level grudge against caddisflies because I blamed them for my lack of knowledge about butterflies. Those two groups of insects might seem very different, but they actually share a close evolutionary relationship, as the orders Lepidoptera (moths and butterflies) and Trichoptera (caddisflies) are considered sister groups comprising a larger superorder called Amphiesmenoptera. Both are named for the appearance of their wings. Lepidoptera means “scale-wing”, referring to the minute overlapping scales that form colors and patterns on butterfly and moth wings. The tented wings of adult caddisflies have tiny hairs instead of scales, hence the name Trichoptera, meaning “hairy wing”. However, the excellent taxonomist who taught me in grad school specialized in caddisflies and had rather less use for Lepidoptera--which is unfortunately the one group that pretty much everyone expects an entomologist to reel off on sight. Hence, my low-level grudge.
However, with time occasionally comes wisdom, and as I began to specialize in aquatic entomology (and do a lot of catch-up learning about butterflies and moths), I gained a better appreciation of this truly remarkable group of insects. Adult caddisflies are mostly dull-colored, with a passing resemblance to drab moths, but larvae are much more creatively attired. Like their caterpillar relatives, caddisfly larvae make silk, extruding it from a gland that opens at the base of the mouth. Some use silk to weave underwater shelters that double as fishing nets for organic debris, while others tie together bits of sand, gravel, leaves, fir needles, bark, or twigs to make intricate portable cases. This architectural adaptation is at the root of the name caddisfly: “cadas” is an Old French word meaning “floss silk” and “cadice” is a Middle English word for a strip of cloth, and itinerant cloth-sellers would pin bright “cadices” to themselves to advertise their wares from afar.
However, with time occasionally comes wisdom, and as I began to specialize in aquatic entomology (and do a lot of catch-up learning about butterflies and moths), I gained a better appreciation of this truly remarkable group of insects. Adult caddisflies are mostly dull-colored, with a passing resemblance to drab moths, but larvae are much more creatively attired. Like their caterpillar relatives, caddisfly larvae make silk, extruding it from a gland that opens at the base of the mouth. Some use silk to weave underwater shelters that double as fishing nets for organic debris, while others tie together bits of sand, gravel, leaves, fir needles, bark, or twigs to make intricate portable cases. This architectural adaptation is at the root of the name caddisfly: “cadas” is an Old French word meaning “floss silk” and “cadice” is a Middle English word for a strip of cloth, and itinerant cloth-sellers would pin bright “cadices” to themselves to advertise their wares from afar.
(Left) Adult caddisflies resemble drab moths, but with hairy wings held rooflike over the body and long, forward-pointing antennae. They also lack the long tubular mouthpart (proboscis) that butterflies and moths use to sip nectar. (Right) Twig...or cased caddisfly larva???? Photos by C.A. Searles Mazzacano, all rights reserved.
Case-making larvae begin constructing their mobile shelters soon after hatching; their silk provides not only binding for the case materials, but also a lining for their clawed anal prolegs to cling to so the case stays with them as they crawl about. Material is added to the front of the case so it grows with them, and they can trim the back to keep it at a manageable length. Cases are roughly tubular but have an astonishing diversity of shapes and materials, from tiny spiraling coils of sand grains created by Snailcase Makers (Helicopsychidae)—such fine mimicry that they were originally classified as snails—to slender plant pieces stacked log cabin-style in square-sided homes of Humpless Case Makers (Brachycentridae), and weighty, tortoise-like gravel domes of Saddlecase Makers (Glossosomatidae). The propensity of mineral case-making caddisflies to use any materials of appropriate size has even led to novelty jewelry, with pendants and earrings made by larvae provided with chips of malachite, lapis, and amethyst.
Caddisfly larvae in Oregon's Whychus Creek (left), Middle Fork John Day (center), and Sandy River (right). Photos by C.A. Searles Mazzacano, all rights reserved.
Small but mighty, caddisfly larvae have a big influence on aquatic ecosystems. Their value as fish food has given them an appreciation among fly fishers that dates back to at least 1653, when Izaak Walton’s Compleat Angler endorsed “cod-worms or caddis” as excellent bait, and today’s fly-fishers can use Sparkle Pupa Caddis, Floating Caddis Emerger, or Crunchy Caddis flies. Caddisfly larvae are eaten by a lot more than just fish, though; they are a solid meal for predatory stoneflies, diving beetles, and waterbirds, and the winged adults are eaten by terrestrial wildlife such as birds, dragonflies, spiders, and amphibians. Caddisflies have practical uses in stream ecology; many prefer running water, where they are one of “The Big Three” orders of insects (the others are mayflies and stoneflies) whose presence in biotic assessment studies indicates colder, cleaner, better-oxygenated waters (though some species prefer the warmer still waters of lakes and ponds). Caddisfly larvae are also ecosystem engineers, a term used to describe organisms that physically modify, create, or maintain habitat. Their silk is strong stuff—strong enough that an abundance of Net-spinning Caddisflies (Hydropsychidae) in a stream can actually help stabilize the gravels they colonize (see Cardinale et al., 2004; Johnson et al., 2010), and case-making caddis can fix tons of gravel and sand to the stream bed, helping to keep the substrate in place even during high flows.
So the next time you find yourself near a stream, pick up a few rocks, turn them over, and wait for some of the stony or twig-like adhesions to poke out a little caterpillar-like head and crawl around—and you too may be drawn further into the beguiling world of caddisflies.
So the next time you find yourself near a stream, pick up a few rocks, turn them over, and wait for some of the stony or twig-like adhesions to poke out a little caterpillar-like head and crawl around—and you too may be drawn further into the beguiling world of caddisflies.
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