Ephemeroptera (mayflies)

The order Ephemeroptera includes the aquatic macroinvertebrates that are commonly referred to as mayflies.  Mayflies are common in many lotic, or moving water environments including lake margins, stream riffles, and rivers.  Some species have larvae that are active swimmers, while others are frequently found buried in the river substrate or beneath stones. 



BaetidaeFamily Baetidae

Small Minnow Mayflies

Members of this family are commonly referred to as small minnow mayflies in reference to the larval form’s strong swimming ability.  Baetid mayflies are found in a variety of habitats ranging from lentic, or still water systems to lotic, or water systems with a moderate to strong current.  These mayflies are collectors and gatherers that have an average larval body length of 3-12mm.  In most species the antennae is two to three times longer than the width of the head.  Baetid larvae also possess three caudal filaments, or tails.  Pairs of gills are located on either side of the abdominal segments.  Baetid larvae are moderately tolerant of poor water quality and they are often found in polluted rivers and streams.

Ephemeroptera Life stage history
Ephemeroptera larvae are known to molt from 12 to 40 times dependent on the species. On average, Ephemeroptera species exist in the larval stage for 3 to 6 months, but some species may exist in the larval form for as little as 14 days, and others for as long as two years.  Mayflies are unique among insects because they have two winged instar stages: the adult and the subimago.  In the subimago stage the insect is winged and above water, but still sexually immature.  It is thought that the subimago stage may reduce the possibility of being trapped at the surface of the water while larva molt to the adult stage.  The length of the subimago stage varies from a few hours to 1-2 days, usually in proportion to the length of the adult stage.  Larvae are aquatic except for the intermediate subimago stage.

Mayflies are part of the subclass Insecta so they have three pairs of segmented legs and a terrestrial adult life cycle.  The antenna of the adult stage are shorter than those of the larval stage, and unlike the larva, the adult mayfly has vestigial, or non-functioning mouthparts.  The adults are most frequently identified by how they hold their wings.  Ephemeroptera is the only order of insects where the insect cannot fold its wings back against its abdomen; consequently, the wings are always held straight up.

The adult stage lasts on average for only 1 to 2 days; thus, adult Ephemeroptera are rarely seen, and the adult stage is not as well researched as the larval stages.  Adults emerge from the larval stage throughout the year.  In some species in which the female lives until the eggs hatch, the female lives much longer than the male of the same species. Mayfly males are often found in swarms 5 to 15 meters above the water’s surface.  Copulation takes place in flight when a females flies into the swarm of males.  The female lays eggs with a sticky coating that are deposited onto the surface of the water in clumps dropped from flight above the water surface; egg development usually lasts a few weeks, but some eggs may lay dormant for up to 11 months until environmental conditions, specifically air temperature, are optimal for development.

Feeding habits
Recently hatched larva feed on small floating detritus, or dead organic matter.  Most larvae are herbivorous collectors and scrapers that eat larger amounts of algae and aquatic plant material as they increase in size though successive molts.  The adult mayfly possesses vestigial mouthparts that are non-functional and it does not eat.

Ecological importance
Ephemeroptera larvae are good indicators of water quality and, serve as a food source for fish as well as bait for fishermen.  Mayflies are most noticeable during the mass emergences that often occur in spring or mid-summer.  The size of these mass emergences has decreased in the past 50 years probably in response to increased water pollution and urban development.

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