So I started reading the usual praise in this article for beavers and all the excellent ecosystem services they provide. And then I noticed that the article wasn’t really about them. It was about Hydropsychid caddisflies. It turns out that these little guys are being researched because when they spin their silky webs to catch a meal the webs actually perform a stabilizing function on the stream gravel which makes it maintain a good spawning bed even during high flows. Think of it like a beaver dam for bugs.

Years ago I wrote a story about spiders that spun webs that saved the stream just as an allegory; Turns out it was prescient.

AUSABLE WATER WISE: Ecosystem engineers of the river channel

If you’ve ever seen beaver take up residence in a stream, you’ll know the incredible power they have to alter their environment. While it can be an inconvenience for landowners, the transformation from bubbling stream to mountain pond, to open meadow, and back into a stream long after the beaver has moved on is an incredible thing to witness.

Flyfishing anglers spend much of their time creating and using lures that mimic three major groups of aquatic insects: mayflies, stoneflies and caddisflies. They tie various flies out of feathers, fur, shiny threads and beads to imitate these flies’ underwater larval stages and the transitional form they take as they move from water to air as adult flying insects. These insects, because of their abundance, are prime food sources for freshwater fish. One particular family of caddisflies, however, have gained a reputation as ecosystem engineers.

What? Sending a bug to do a beavers job? Is this for real?

This locally abundant family of caddisflies, called the Hydrophsychids, spend most of their water bound time spinning nets of silk that they put out into the river current to catch drifting food particles. The silk is not as strong as spider silk but is strong enough to withstand high water velocities. It is a very efficient way of collecting food, so much so that this family of insects thrives in both wild and heavily human altered rivers. But the nets do more than just providing food for the caddisflies.

Recent research suggests that the Hydropsychid caddisfly family may actually be engineering stream systems. We already knew that their nets slow the water velocity just above the streambed. This creates suitable, lower velocity habitat for many other species of aquatic insects. Just like a beaver dam creates extra habitat for fish, amphibians, dragonflies, and birds, the Hydropsychid caddisflies open up more habitat for more diverse species to move in and shelter or feed from the faster currents. But wait, there’s more.

When these aquatic insects put out their silky nets into the current, the ends adhere to pieces of gravel on the streambed. Looking more closely, river ecologists realized the silk can actually hold gravel and cobble substrate together, preventing movement and erosion during moderate to high flow events.These nets actually stablilize the streambed.

Whoa. I need to sit down. This is fully blowing my mind. Millions of bugs making millions of tiny nets that act like beaver dams and slow down the water. I bet no one ever complains about them blocking culverts either! I guess those little flies are very important.

Good thing there’s so much research proving that beavers improve things for them.

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