Mayflies

Order: Ephemeroptera

Life Cycle: incomplete

Three Life Stages: egg-aquatic nymph, and adult cycle which includes two phases: (subimago) dun and (imago stage) spinner

Species: over one thousand

Hatch is over a one to three week period yearly

Mayflies undergo an incomplete metamorphosis, meaning that typically in a one year period they go through three cycles: egg, nymph and adults. Most of the mayfly’s life is spent in the nymphal cycle.

There are four different groups that the mayflies are divided into depending on body type and behavior. These are: burrowers, clingers, crawlers and swimmers. Burrowers have an oval, long-shaped body with fringed gills and very visible tusk-like mandibles. The clinger mayfly has a head wider than the abdomen and a flattened body. Crawlers have a head equal to, or less than, the width of the abdomen and have a slightly flattened body. Along the top margin of the abdomen are forked gills; except for a few species they have no tusk-like mandibles. The round, streamlined body of the swimmer has a head equal to, or less than the width of its abdomen. Swimmers have tails where the edges are fringed with fine hair.

Nymphs grow as they molt 20 to 30 times and their wing pads darken as their wings start to develop. As the mayfly nymphs start to emerge, most of them

swim or drift to the surface and emerge as adult mayflies. Some of the mayfly nymphs emerge under the water and must swim to the surface, or they may crawl out to the shore and hatch.

The adult mayfly goes through 2 phases. The first is a dun and the second phase is commonly called a spinner. The newly hatched adults are called duns and fly to the steam’s foliage after emergence. In this dun phase the adults are unable to mate and have opaque wings. The spinner emerges anywhere from one hour to 3 days after the dun sheds its outer covering. The sexually mature spinners have clear wings and form mating swarms in the air. When a female comes into the swarm she is seized by a male and mating takes place. After mating, the male usually falls spent to the water or ground and the female begins depositing her eggs on the water’s surface or sometimes underneath the water. Then she falls spent, creating a spinner’s fall. Trout enjoy most of the phases of the different 4 groups, having interest in some more than others.