Silk threads are woven by caddisfly larvae into a mesh-like lattice that is used to catch food from the water in stream habitats. The width and length of each rectangular pore are approximately 100 x 175 micrometers. Credit: L. Albertson

Plants and animals in streams alter the way sediments flow and channels form. Among these species are the miniscule caddisfly larvae, which measure less than a centimeter in length but populate many streams in large numbers.

Albertson et al. collected the insects’ silk nets along creek bottoms and showed that caddisflies can collectively slow gravel transport to half the rate seen in areas where their populations are more sparse. The larvae of the tiny, moth-­like caddisflies are underwater architects known for making silk webs and cases that they attach across rocks underwater to catch food.

The researchers looked at nets of two species of caddisflies in creeks near Mammoth Lakes, Calif. Each insect’s net was removed from the rocks by hand and carefully transported to a laboratory.

There, the team did stress analysis tests to find the net’s tensile strength. Under a microscope, the lattice looks something like a tiny rectangular wire fence. In running water, the net holds together everything from plants and debris to rocks and sand. When the researchers stretched the silk, they found that one species, Arctopsyche, had nets that tested about 25% stronger than those made by their cousins, Ceratopsyche.

The team introduced thousands of caddisflies per square meter into a laboratory test with creek water and propellers for flow and simulated streambeds with various sizes of gravel grains. Once both species of insect had settled in, the researchers found that their nets significantly slowed sediment washing downstream. The effect lessened as the size of rock increased.

Although more research is clearly needed, the authors suggest that even small and seemingly insignificant organisms like caddisflies may have large impacts on physical processes like erosion, habitat formation, and nutrient cycling. (Journal of Geophysical Research: Earth Surface, doi:10.1002/2013JF003024, 2014)

—Eric O. Betz, Writer

Citation: Betz, E. O. (2014), Silk insect nets can reshape creek beds, Eos Trans. AGU, 95(50), 472, doi:10.1002/2014EO500010.

© 2014. American Geophysical Union. All rights reserved.

© 2014. American Geophysical Union. All rights reserved.