Last week a mayfly hatch was reported along the Upper Mississippi River between Winona, Minnesota and Guttenberg, Iowa. The doppler radar loop on weather news sites shows the reflection of this mass emergence.
Yesterday, when we stopped at one of the overlooks along Highway 35 south of La Crosse, Wisconsin, the vegetation in shady spots was a refuge for some survivors. Some plants had as many as a dozen clinging under leaves and along stems. The adult stage is usually just a few days; time for them to mate and lay eggs.
There are many species of mayflies. One book we have (The Angler’s Guide to Aquatic Insects and Their Imitations by Rick Hafele and Scott Roederer) describes a key for sorting them into four groups: swimmers, crawlers, clingers and burrowers. These groupings are based on nymph behavior as the nymph stage is the longest part of the mayfly life cycle.
Trying to key out from photographs is very difficult, especially for novices. The large body seemed to belong to the burrower group but it only has two tails and burrowers have three. We decided to settle on admiring the shape and beautiful, black iridescent wings.