Warm days above freezing in January are a good time to look for winter stoneflies. Winter stoneflies emerge in the dead of winter and can be found basking on the sunny side of bridge piers.
Stoneflies have a number of strategies for surviving brief cold spells. Their hemolymph (blood) contains anti-freeze chemicals such as sugars and glycols that depress the freezing point of the blood by several degrees below freezing. At night when the temperature drops or on days with extreme cold, there are parts of the outdoor environment that stay warmer than the air temperature. These include air pockets under the snow and crevices and tunnels in rock and soil.
Winter stoneflies emerge to mate at a time when the predatory birds have gone south for the winter. Only a short time is spent as adults who must mate and lay eggs before they succumb to the harsh winter conditions. This week is a good time to observe stoneflies in west central Indiana.