Winter Midge

Appearance

Diamesa mendotae is a member of the non-biting midge family Chironomidae. Although mosquito-like in size and appearance, adult D. mendotae do not bite, or even feed! Males have prominent, plumose antennae, and females are overall larger. The aquatic larvae are small (~10mm), soft-bodied, and worm-like with a hard head capsule.

What do they eat?

Adult D. mendotae have reduced mouthparts and are not known to feed, but the larvae eat algae and microorganisms growing on rocks and other substrates underwater.

Where and when do you find them?

Unlike most insect species, D. mendotae is winter-active! You may find D. mendotae at temperatures well below freezing walking along snowy banks of groundwater-dominated streams, which remain ice-free all winter. Here’s a short video showing a female walking on the snow. At slightly higher temperatures, swarms of flying D. mendotae may be found around these streams as they search for potential mates.

Importance to Minnesotans

As a common member of groundwater-stream ecosystems, D. mendotae are a food source for brown trout and other fish species. Trout fishing is an extremely profitable industry in Minnesota, thus D. mendotae and other winter-active aquatic species are important to ensure streams remain inhabited by trout.

Fun Fact

Diamesa mendotae is very well adapted to the winter. Adult D. mendotae can survive freezing below -20°C (-4°F) by suppressing their freeze-point with “antifreeze” biomolecules in their blood (hemolymph). This ability allows them to remain active throughout the winter when most other insects become dormant!

For more information

Chironomidae Research Group
BugGuide.net
iNaturalist.org
Macroinvertebrates.org
Bouchard, R. W., & Ferrington, L. C. (2009). Winter growth, development, and emergence of Diamesa mendotae (Diptera: Chironomidae) in Minnesota streams. Environmental Entomology, 38(1), 250–259. https://doi.org/10.1603/022.038.0131

Author

Hannah Bodmer

Photo Credit

Third photo: Hannah Bodmer

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