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Written By Karl VonBerg.

Posted on April 29th, 2021.

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Would you ever guess a one-inch, worm-like larva could slow erosion in a stream?

What is a caddisfly larva? A fly fisherman will know. Much of their fishing success depends on copying this little critter. Have you ever seen a lot of insects that are flying all over at sunset, get stuck to your windshield, and swarm around lights? The adult caddisfly does this along with mayflies. The larvae are one-inch, worm-like critters that live in streams, ponds and lakes.


#1 Caddisfly larva

Many caddisfly larvae glue together stones, sticks, leaves or other items to create a tube to live in. Some spin a net which allows them to catch their food. These nets also hold the stones on the bottom of a stream together, so they don’t wash away as easily. This helps to improve stream stability.

Why is this important? Stability is what gives a stream a place for critters to live. This stability gives rise to a whole community of animals that live together and depend on each other (aka an ecosystem). If the stream bottom was constantly moving and shifting, it wouldn’t be able to provide that stability.

So the net-spinning caddisfly larva is an ecosystem engineer that both creates a habitat (place where an animal lives) and maintains it. Can you think of another ecosystem engineer that we are all familiar with? One that builds dams. The beaver. Check out what these engineers do:


  • Build ponds to live in
  • Ponds slow water flow and provide water storage during both low and high flow periods
  • Ponds provide a home for other animals

Caddisfly Larvae

  • Build nets for shelter and trapping food
  • Netting holds the stones together at the bottom of a stream, keeping them from washing away
  • These stones provide a home for other animals

Caddisfly nets can prevent orange-sized rocks from washing downstream during a storm! Caddisfly larvae are an important part of a food chain involving a whole series of critters:

Insects, plankton, algae, diatoms and plant debris > feed caddisfly larvae > feed fish > feed osprey and eagles

Many of the net spinning caddisfly larvae don’t survive well in polluted water. If they don’t survive, the food chain is broken and other animals are affected. We can play a role in keeping this food chain intact by helping to keep streams clean.

Like a caterpillar larva that becomes a butterfly, the caddisfly larva will transform into an adult caddisfly and emerge from its watery home to mate and lay eggs for the next generation of caddisflies.


#2 Caddisfly Adult

So if you get caught in a “hatch” and see these adults flying all over some night (and making a mess of the front of your vehicle), realize they are carrying on the amazing net-spinning, erosion-slowing characteristics of the caddisfly to the next generation.

[By the way, the adults drink but can’t bite because they have no mouth parts.]

Here are some pictures of net spinning caddisfly larva.

Checkout this short video about the net spinning caddisfly.

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