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Netspinner Caddisflies (What Time is it in Nature)

March 7, 2015

This week’s What Time is it in Nature is brought to you by Sehdia Mansaray, Prairie Ridge intern for the spring 2015 semester.  Sehdia is a student at North Carolina State University and is double majoring in Environmental Science and Anthropology with a minor in French. She is interested in the relationship of human populations with their natural environment.

If you look closely in the Prairie Ridge stream where the water current is just right, you can find netspinner caddisflies in the caddisfly family Hydropsychidae.  Netspinners are closely related to moths and butterflies (you may have seen an adult caddisfly fluttering around your lights at night and mistaken it for a moth), but their anatomy and life cycle are quite different. These aquatic insects spend most of their lives in streams and other fast flowing waters worldwide, but species vary in habitat, diet, and life cycle.

Netspinner caddisflies

True to its aquatic nature, adult female netspinner caddisflies dive underwater to lay eggs on the undersides of submerged stones. Most eggs take a year to develop into larvae, but they can take up to two years in some areas. As a larva, netspinners have a tan or green body with three armor-like plates on the upper surface of the thorax. Gills and small hairs line the underside of the curved abdomen. Netspinners undergo five to eight instars (growth stages) in which they metamorphose and molt as larvae.  Mature larvae, those about to transition into the pupal stage, average from 10mm-30mm in length.

The larval stage gives the netspinners their common name: they spin silk nets to capture food. The water current in their habitat allows food particles to float by such that they may be easily caught in nets. Larvae thus spin silk nets on or between rocks where they can capture insects, algae, diatoms, and any other food particles floating downstream on the water current:

Caddisfly net

The stronger the current, the stronger netspinners make their nets.

After spending most of its life as larvae, netspinners enter the pupal stage.  As pupae, they exhibit antennae and hooked plates on the abdomen. As netspinners transform from larvae to adults, their diet changes from omnivorous-detritivorous (eating and breaking down dead plant and animal materials) to nectarivorous (feeding on nectar). As adults, netspinner caddisflies exhibit 5-segmented, long maxillary palps (mouthparts) that assist them in feeding on nectar, and dotted brown wings for their new terrestrial lives. You’re likely to see a swarm of adults during summer nights when they breed and in some areas the numbers of adults can become so numerous that they become a nuisance. Adult netspinner caddisflies generally don’t live longer than a month.

The common netspinner is used for both recreational and environmental assessment purposes. Fly fishermen often use common netspinners as bait for trout. Because they filter food from the water and break down plant and animal materials in streams, they have also been extensively studied as biological indicators of aquatic system health.

It’s amazing to see the nets constructed by the netspinners and consider how such a tiny home can have such a big impact. Come see netspinner caddisflies for yourself in the Prairie Ridge stream!

What Time is it in Nature is a weekly feature highlighting the current plants, animals, and other wildlife at the Museum’s public outdoor facility, Prairie Ridge Ecostation.Find out more about the natural happenings at Prairie Ridge at our What Time is it in Nature Archive!

(Photos by Chris Goforth)

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