About Mayflies


Kingdom: Animalia (Animals)

Phylum: Arthropoda (Arthropods; jointed external skeletons)

Class: Insecta (Insects)

Order: Ephemeroptera (Mayflies)

Family: Ephemeridae (Common Burrower Mayflies)

Genus: Hexagenia spp. (golden mayflies, giant mayflies, burrowing mayflies)

Species: (5 species of Hexagenia in North America)

Mayflies are ancient insects belonging to the order Ephemeroptera, which in Greek means short-lived (ephemeros) and winged (pteron). Their life cycle includes four stages; 1. eggs, 2. larvae also called naiads or nymphs, 3. sub-adults also called sub-imagos or duns, and 4. adults also called imagos or spinners. Other common names for mayflies include dayflies, fishflies, Canadian soldiers and shadflies. The larval stages are aquatic and live in freshwater streams, lakes and ponds, although some species can tolerate brackishwater. There are about 2,500 species of mayflies worldwide, with less than 700 species belonging to 21 families in North America. Most mayfly species are pollution sensitive and cannot survive in waters with low dissolved oxygen content. Their presence in a water body is one indication of good water quality.

Most mayfly species have a one-year life cycle, although their life spans can range from weeks to several years depending on species, water quality, temperature and food supply. Larval mayflies are mostly herbivores and detritivores feeding on microscopic algae and small organic matter in water. Sub-adult and adult mayflies do not feed and typically live only a few hours to a few days. Digestive tracts of sub-adults and adults are filled with air that helps them float on water.

Ephemeroptera are unique by being the only group of insects that molt after they have wings. The sub-adult, winged stage quickly transitions between the larvae and adult. Many mayfly species emerge from the larval stage in mass in what is called a hatch. The hatch typically occurs at about the same time each year in many places when large numbers of mayflies emerge from the water, breed, and die soon thereafter. In some places, hatches include very large numbers of mayflies that accumulate under streetlights and other lights at night. Masses of dead mayflies often must be removed in bucket loads. Lake Erie and some other of the Great Lakes are known to produce enormous hatches of burrowing mayflies like the golden mayfly.

Mayfly larval stages are characterized by three long, thin tail projections or cerci (some have only 2) at the end of the abdomen, and 7 pairs of plate-like gills on the abdomen. Larval body lengths typically range from 2 to 32 mm (0.08 to 1.3 inches). Mayfly larvae provide an important food source for many fishes and other aquatic animals.

Sub-adult and adult mayflies have delicate bodies and wings. Their veined wings are held vertically above the body when at rest, and are almost transparent in the adult stage. Fore wings are larger than hind wings. Hind wings are absent in some species. Sub-adults have more opaque wing color. Adults have 2 or 3 long tails, and long fore legs. Eyes are large and well developed, especially in the males. Sub-adults have duller color and less transparent wings, but are otherwise similar to the adults.

Mating takes place when adult males swarm 15 to 50 feet above ground and females fly through the swarm where males grasp them and breeding takes place. Females then deposit eggs into the water. Some species lay eggs by dipping their abdomens into the water, while other species land on the water or dive under water to deposit eggs. Eggs hatch into larvae that go through several molts before becoming sub-adults and adults.

The sub-adult, duns are favorite food of stream fishes such as trout. Fly fishermen try to create artificial baits that mimic or resemble the sub-adult or adult mayfly species that are hatching at a given time and place. This is an art form that separates avid fly fishermen from other fishermen.

References Books:

McCafferty, W.P. 1981. Aquatic Entomology; The Fishermen’s and Ecologists’ Illustrated Guide to Insects and Their Relatives. Science Books International. 448 pp.
Merritt, R.W. and K.W. Cummins (eds.) 1978. An Introduction to the Aquatic Insects of North America. Kendall/Hunt Publishing Co. 439 pp.
Usinger, R.L. (ed.) 1963. Aquatic Insects of California; With Keys to North American Genera and California Species. University of California Press. 508 pp.
Knopp, M. and R. Cormier. 2002. Mayflies: An Angler's Study of Trout Water Ephemeroptera. The Lyons Press. 388 pp.

Reference Websites:


USGS Northern Prairie Wildlife Research Center:

MAYFLY CENTRAL Purdue University

US Environmental Protection Agency

Ephemeroptera Galactica Florida State University

The Almost Official Mayfly Page