Let’s Talk Bugs
by Tom Lager

Looking through my “bug books” the other day, I came across a very unique caddisfly larvae. The uniqueness is in the type of larval case it constructs. As you know, almost all caddisfly larvae construct cases. This larva makes a case similar in structure to that of a snail shell. Consequently, it has been named Helicopsyche by scientists – “helico” in reference to the spiral or helix shape the case is formed into.

This case, like all other caddis cases, provides camouflage and protection for the larvae; however, the reason for this shape is an intriguing question. In my view, there is always a reason for what occurs in nature – our creator knows the answer and many times we are left to guess or experiment to find the answers. I have observed these caddis larvae on smooth rock surfaces in the Waupaca and Wolf Rivers in areas with a swift current; they are small in size, about 5 mm across during mid-summer.

Some researchers report the larger sized ones occur in faster water – perhaps the larger size and weight provide ballast to help maintain their position against the current. Additionally the spiral shape may provide a streamed line profile that reduces drag – the effect of water flow working against the surface. Another thought, is a spiral structure may provide excellent structural strength, since it is made of “domes with interior walls”. Strength of a case is likely key when we as fisherman tromp over the rocks and when the rocks are rolled and scrambled during heavy flows following rain storms, Another potential advantage is that the larva can add new layers of sand grains to opening thereby extending the spirals to enlarge the case as the larva grows. The ability to enlarge the case without having to abandon it to build a new case reduces exposure to predation from trout and other insects.

As for how Helicopsyche larvae are important to us as trout fishers, maybe in this case (small pun intended), the main value is just knowing about them and what they do as they inhabit our streams. The Helicopsyche larve feed mainly on algae and other substances growing on the rock surfaces. They crawl around pulling the case and scrape food from the rock. They are likely infrequently available as trout food except when they drift in the current outside of their case as a means of population dispersal. The adults, known as the “Orange Sedge” emerge in mid-June to early July in our region, after pupating in late spring. The emergencies are not large, but are sporadic. Elk wing patterns are effective as imitators.

Remember as you traverse our streams in search of trout, “take the time to look at the bugs” – sort of like taking time to smell the roses.