Aquatic Winter Insects in Delaware

By: Ginger North, Citizen Science Coordinator

Although most insects are not active in the winter in Delaware, there is one group that is happy when the weather turns cold. Aquatic insects love the winter because cold water holds more oxygen which they need to live. Aquatic insects (formally called benthic macroinvertebrates) are important indicators of water quality. In fact, Delaware has a State Macroinvertebrate, the stonefly!

 

Stonefly larvae Photo by Morenci students in Michigan
Stonefly larvae - Photo by Morenci students in Michigan

Stonefly larvae are very sensitive to low levels of oxygen and their presence is an indicator of excellent water quality. There are several types of stoneflies native to Delaware’s rivers and streams. One type is called the winter stonefly because it actually emerges as an adult on warm winter days. If you are out walking near a high quality stream in the winter, look for these small black insects on the river banks. They are easier to see if there is snow on the ground. 

Adult Winter Stonefly on snow
Adult Winter Stonefly on snow

 

 

You can see the larvae in the water at any time of the year, although fall and early spring are especially good times as the larvae are larger than in the late spring and early summer. If you are lucky enough to find these “stream critters”, it indicates that you are looking in a stream with excellent water quality.

Mayfly - Photo by Valley City State University staff
Mayfly - Photo by Valley City State University staff

 

Caddisfly Larvae
Caddisfly larvae
Cranefly larvae - Photo by Michael Clapp
Cranefly larvae - Photo by Michael Clapp

 So get outside and check out the leaves and rocks in the creek. There are lots of aquatic insects in Delaware’s streams, including caddisflies, mayflies, and craneflies to name a few. If you are really lucky you might be able to find the State Macroinvertebrate!  For information about adopting a local stream to evaluate, and future Stream Adoption Workshops, email me at ginger@delawarenaturesociety.org.

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