Winter Stoneflies

By Susan Post

The life of fall and winter stoneflies is an exception to the rule that insect activity ceases with the approach of cold weather. Twenty species of the state's 65 native stoneflies emerge during November through March. With a habit of congregating in places exposed to the warming sun's rays, you can see them crawling about on exposed tree trunks, fence posts, or on rocks located close to a stream. The white concrete bridges characteristic of Illinois' highways are a beacon of warmth to a stonefly.

Stoneflies belong to the insect order Plecoptera. In appearance stoneflies are about a half an inch in size, have two pair of wings, and are rather drab in color. The adults, although terrestrial, are seldom found away from water. They are poor fliers with crawling the preferred mode of transportation. The eggs and nymphs are aquatic. The nymphs are often found under stones in streams, hence the common name —stonefly. The nymphs of the winter stoneflies are chiefly plant feeders. The adults feed on blue-green algae or not at all. The nymphs emerge from the water, find a suitable perch and metamorphose into an adult. The adults mate, lay eggs and die, usually living less than a month. The whole life cycle is complete in a year.

Although sunbathing in Illinois from November through March generally lacks appeal to most humans, the bridges over creeks emptying into the Middle Fork of the Vermillion River, or the clear, rocky streams of Southern Illinois are perfect places to absorb the fleeting sunlight of winter and to see Illinois winter stoneflies.

January 24, 2010

White concrete bridges

Beacons of warmth

Nude sunbathers gather

Looking for love

Absorbing weak sunlight

Coupled in pleasure

Winter stoneflies above Stoney Creek

On 8 March, 2010, winter stoneflies were observed on the bridge over the Middle Fork of the Vermilion River at Kickapoo State Park.