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Winter Stoneflies Provide Cold-Water Forage Opportunity

A snowy creek bank teeming with insects? Not exactly what you would expect to see on a winter day. Because insects are cold-blooded and need warmth to function, they typically avoid cold conditions by hibernating or finding shelter. A few, such as green darner dragonflies and monarch butterflies, migrate. Winter stoneflies do the unexpected: they brave the cold.

Winter stoneflies, though uncommon in our area, are peculiar little creatures. In the dead of winter, these stoneflies’ aquatic immature stages, called larvae or nymphs, crawl from their rocky bottom home to the surface of the stream they’ve inhabited for the last year and emerge as adults. They don’t need just water to survive, they need cool, well-oxygenated water that is very clean, for they are also intolerant of pollution.

As they mature and emerge from the water, stoneflies drum to attract a mate. The male stoneflies are the ones that initiate the drumming. They tap their abdomens against a surface, such as a log. Female stoneflies then indicate their interest by drumming back in a simplified response pattern. If you’re not a stonefly, you’ll need special equipment to hear the sound. Females then head to a nearby waterway for egg deposition, while males go back to drumming.

How can they be so active in sub-zero winter temperatures? They actively produce anti-freeze compounds – including glycerol, proteins, and sugars – that allow their body fluids to remain unfrozen at temperatures below freezing. The insect’s dark color also helps them absorb warmth on sunny days and makes them stand out quite starkly on the white snow.

As you are out hiking along your favorite stream, keep a close lookout for these unique stoneflies that are hatching now. For more information on stoneflies visit mdc.mo.gov.

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