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SCIENTIFIC NAME: Ephemeroptera

There are 2,100 described species of mayflies. 
  • About 700 of the species can be found in North America.
  • Mayflies live all over the world, except in the Arctic and Antarctic.
Mayfly larvae are usually detritivores or herbivores, with diets mainly consisting of detritus and algae.

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                                                                               Source: University of California Museum of Paleontology

  • They may collect food by grazing as they move over stones and weeds.
  • Some species have special adaptations for filter feeding, which allow them to feed on small food particles in the water.
  • Some larger species may also be carnivorous and predatory.
  • In general, mayflies aren't picky; they eat what they can, when they can.
Mayfly nymphs are always aquatic, but their specfic habitat depends on the species.
  • Each species survives best in an environment with a specific substrate, depth, oxygen level and amount of wave action.
  • Generally, mayfly nymphs tend to live in streams, but some can also be found in still waters.
  • They are most common in waters that are cool, clean and shallow, such as shallow streams and at the edges of lakes near the shore. 
  • They like to burrow into the substrate in areas with sediment deposits, and may have a specific preference of substrate particle size or aquatic plant depending on the species.

Mayflies undergo incomplete metamorphosis as they do not have a puapl stage. This involves passing through 3 life stages which are egg, nymph and adult.

  • After mating, the female mayfly lays her eggs by dipping them into the water while flying, releasing a few eggs with each dip.
  • Another technique is to deposit the eggs on the surface of lakes and streams, where they sink and scatter among aquatic plants and debris.
  • Mayfly nymphs emerge shortly after the eggs have been laid.
  • The new hatchlings are less than 1 mm long and have no gills, bearing little resemblance to the adults they will become.
  • Throughout their development, the mayfly nymphs can grow up to 3 cm long, passing through many stages of development (called instars).
  • The number of instars (stages of development) depends on the species, but can range anywhere from 12 to 45, however most have about 15 to 25. 
  • The nymphs live in the water, along the bottoms of freshwater habitats where they can take shelter in the substrate. 
  • As nymphs become older, they develop gills, and some signs of their gender can be seen in the last few stages before adulthood.
  • The length of the nymph stage varies depending on the species of mayfly, along with the water temperature and the geographic location.
  • The nymph sheds its outer layer (called 'molting') by emptying its guts and filling its mid-section with air while floating up to the surface of the water at the same time. When it gets to the top, its outer layer splits open and the wings come out.
  • After a very vulnerable period during which the subimago is soft and too weak to fly, it gains some strength and then flies from the surface of the water to a more sheltered place, like a tree or among tall grass.
  • It stays sheltered and rests until its final molt, which occurs within 24 to 48 hours, leading to the final stage of the mayfly, called the 'imago'.
  • Development to the adult stage can take anywhere from several months to a year.
  • Mayflies two adult stages; both of them have wings, live only for a short time, and do not feed.
  • The first of these stages, which is called the 'subimago', is a sexually immature stage in which the wings are covered with tiny hairs.
  • The second transformation is called the 'imago'. It has shiny, clear wings, and has more rapid flight than the subimago due to its longer legs and tail and is sexually mature. This life stage lasts from only a few hours to at most, a few days.
  • The imagos need calm weather for mating due to the fragile nature of their wings.
  • They usually mate while flying in large swarms gathered close to fresh water habitats .These swarms may be so dense, that if you are driving through one it may be difficult to see where you are going.
  • Males tend to swarm close to the water, attempting to mate with any females that enter the swarm.
  • Each species have a unique flying pattern so that females can recongnize the male of her species.
  • When a male has succeeded in mating with a female, he guards her to prevent any other males from mating with her.
  • Adult mayflies usually emerge from late spring to early fall, after which they mate in swarms, lay eggs, and then die.

Mayfly nymphs provide food for many types of fish, such as trout, in lakes and streams.
  • They are also eaten by parasitic round worms, flies, water beetles, frogs, and birds. 
  • While in the first adult stage, Mayflies can be eaten by dragonflies and water beetles, birds, and fish.
  • Mayfly eggs can be a source of food for caddisfly larvae and snails.
  • Mayflies are the only insect that has a winged immature stage.
  • Adult mayflies have two pairs of transparent wings that are held vertically above their body at rest.
  • Adults have no mouthparts or gills because their function is to reproduce. After they reproduce, they die.
  • The name mayfly is based on the fact that the adults often emerge in the month of May.
  • Nutrition has no effect on the number of instars a mayfly goes through during development, but it does influence the increase in size of each instar.
  • If the nymphs are threatened, they may raise their three tails and the end of their abdomen in a posture that resembles a scorpion. If this posture fails to drive away the intruder, the nymphs may even extend their tails over their bodies. This interesting behavior may make the nymphs appear larger to potential predators.

Brusca, R. C, and Brusca, G. J., 2003. Invertebrates, 2nd ed. Sinauer Associates, Inc., Publishers, Massachusetts. Page 595-596.
Canada's Aquatic Environments (2002). Ephemeroptera. Available here.
DMI International Corporation (2003). LaMotte Aquatic Macroinvertebrate Insect Identification Flashcards.
Soil & Water Conservation Society of Metro Halifax (2006). Order Ephemeroptera. Available here.
The Commonwealth Scientific and Industrial Research Organisation (2009). Ephemeroptera: mayflies. Available here
University of California Museum of Paleontology (2010). Ephemeroptera. Available here.