Common Name: Mayfly
Scientific Name: Varies
Order: Ephemeroptera

Description: Subimagoes (pre-adults) and adults (imagoes) have large triangular front wings with many cross veins with the wings held upright and together over the thorax.  Subimagoes have the wings cloudy in appearance while imagoes have clear wings. Some species may have the wings patterned.  Hind wings are much smaller than the fore wings and may even be absent in a few (mostly small) species.  The thorax and the abdomen of mayflies are bare and often shiny.  Legs vary in size, with the front legs the longest and held forward when at rest.  Body color varies with species, including yellow, green, white and black.  Adults and immatures are quite delicate. Aquatic immature stages are elongate, and flattened or cylindrical.  Immature mayflies (naiads) have long legs and plate-like gills on the sides of the abdomen, they usually have three long thin tail projections (cerci) but a few species only have two.  They have short antennae.  Their body color may be green or brown but may vary by the food that is eaten.  Flattened forms attach themselves to rocks or other substrates in streams. Cylindrical forms are better swimmers.

Our largest species is Hexagenia limbata (Serville) which can be nearly an inch long not including the tails. This species is yellow or yellow-green and may be found along the edges of lakes where the naiads burrow into mud. Some of the most abundant species are Baetidae, Caenidae and Tricorythidae are also common and some of these are barely a quarter of an inch long as adults.

Life Cycle:    Adult mayflies are very short lived, surviving only one or two nights. During that time the adults mate in swarms in the air. They are also attracted to lights. Eggs are deposited while flying low over the water, or by dipping the abdomen on the water surface or some even submerge themselves and lay eggs underwater. Adult females lay eggs into water and often die on the water surface.  Immature stages develop through several stages (instars) by molting during development.  The number of molts varies depending on the species, temperature and water conditions. Immature stages then swim to the water surface or crawl onto rocks or plants.  There, they molt into subimagoes with wings in seconds or minutes, which fly quickly from the water to nearby plants where they molt again into adults (imagoes). Mayflies are the only group of insects that molt after they have wings. In all other orders winged forms are as only found on adult forms, the last stage of development. A typical life cycle will last one year.

Habitat, Food Source(s): Immature stages (naiads) have chewing mouthparts; adult mayflies do not feed and have non-functional mouthparts.  Mayfly immatures (naiads) are aquatic and feed by scavenging small pieces of organic matter such as plant material or algae and debris that accumulate on rocks or other substrates in streams.  Most of the species in Texas prefer flowing or highly oxygenated water situations. A few species develop in lakes or ponds and their distribution in water is usually limited by oxygen content of the water.

Pest Status: Common aquatic insects that generally go unnoticed; occasionally, large numbers of adults (and subimagoes) emerge during certain times of year in synchrony and are sometimes abundant enough to be a nuisance; most problem situations occur when they are attracted to electric lights at night.  They are medically harmless. Immature mayflies are an important food source for fish. Many lures and artificial flies are patterned after them.

Management: No management required, not considered a pest.

For additional information, contact your local Texas Cooperative Extension agent or search for other state Extension offices.

Literature:  McCafferty 1981. Reviewed: Baugh 5/97.