Nature Notes: Underwater architects — caddisfly larvae and their unique homes

Published 5:39 pm Tuesday, June 4, 2024

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By Kelly Bahl

Outreach Naturalist

The Jay C. Hormel Nature Center is home to so many critters, but not many know about the plethora of them that live under the surface of our waters. Both our pond and Dobbins Creek are amazing habitats for all sorts of aquatic macroinvertebrates which is a fancy phrase for all sorts of water creepy crawlies that don’t have a backbone, like bugs, or crayfish. Those aquatic insects are usually in their mid-life stage underwater before they become their better-known adult stages in the air and on land, like dragonflies, damselflies, mayflies, etc.

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One of the coolest macroinvertebrates in the creek scene are little grub looking insects called caddisfly larvae. Their adult form is similar looking to a moth that lives for about four months. Most of their life is spent in their aquatic larval stage, which could last a couple of years hanging out in streams and rivers. While the appearance of these glorified worm looking inverts is nothing to write home about, they are incredibly talented underwater architects.

Caddisflies larvae produce sticky silk because of modified salivary glands. Can you imagine being able to spit out double sided tape on command that works in water? What a party trick. These larvae take this sticky silk and construct a huge variety of different structures. Some of them will create intricate tubes made from individual grains of sand, pebbles, or plant material. While others can make more of a snail shell shape, or even just weave a net out of silk.

After the construction, the caddisflies that build these tubes, called casings, crawl inside, like a hermit crab does. They will attach themselves with their newly self-constructed home to a rock on the bottom of the stream bed to lie in wait for food to come to them.

An up-close look at these little architects proudly hunkered down in their casing will showcase three pairs of legs and heads hanging out the front to catch a meal from the water current on the way by. The front of their heads house large pincers that help chomp through dead organic material including algae and leaves, called detritus.

It is easy to spot caddisflies as most are attached to rocks on creek bed floors. You can find small streaks of webbing silk, suspicious rocks clumped together, or, if you are lucky, find intact casings if you turn over rocks in a cold, fast moving creek. In recent years more and more caddisflies and their casings have been found in Dobbins Creek at the nature center which is a great indication of water quality. Caddisflies, along with some other macroinvertebrates, have a low tolerance to pollutants in the water where they reside. Meaning the more that we find, the cleaner our water quality is.

Caddisflies, stoneflies, mayflies, and other aquatic macroinvertebrates are a primary food source for larger aquatic animals that live in streams, including trout. An increase in these pollutant intolerant aquatic macroinvertebrates shows us that there has been an improvement to the water quality over the past few decades. Next time you are enjoying time at a babbling brook or taking a stroll next to Dobbins Creek at the nature center, know that there’s a lot happening beneath the water’s surface.

Nature Center

June Calendar

June 5: 4th Ave Fest Free Canoeing at Mill Pond, 5-8 p.m.

June 8: Free Naturalist Led Hike, 10 a.m. and 1 p.m.

June 13: Senior Special, 10 a.m., Free Nature Play, 1-4 p.m.

June 14: Cedar River Astronomy Club Meeting, 8-9 p.m.

June 15: Volunteer Forest Restoration, 10 a.m.; Sola Fide Observatory Public Viewing, 9:30-11 p.m.

June 19: Interpretive Center Closed

June 22: Free Nature Play, 1-4 p.m.

June 27: Senior Special, 10 a.m.; Free Nature Play, 1-4 p.m.