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Ephemeroptera: General Information
Mayflies
Eintagsfliegen

The life cycle of mayflies
Oviposition differs from species to species. The females of some species (e.g. most Baetis species) dive into the water of ponds or streams and deposit their eggs under stones or other suitable substrates. In other species, the females do not submerse in water and rather land on objects in the water and glue their eggs to the substrate below the waterline. In other species the females land on the water surface, release their eggs and then die by drowning. In many species, however, the females deposit their eggs in flight by quickly touching the water surface with their abdomen or by simply dropping the eggs into the water. The eggs deposited in this way quickly sink to the ground. The females of Cloeon dipterum do not deposit eggs; rather the females rest immotile and without food uptake near the water for about two weeks until the larvae have hatched from the eggs still within the female. The female then distributes the 600 to 700 small larvae during flight. Embryonic development usually takes 10 to 20 days, but also depends on water temperature, and in a few species the eggs are a diapause stage. The eggs are mostly oval and less than 200 µm long. Usually they have an outer layer that takes up water to become a sticky, jelly-like substance that sticks to the substrate. The animals hatch with strong muscle movements and use an egg-tooth to rupture the egg-shell. In addition, the animals take up a large amount of water and amniotic fluid which helps to burst the egg shell. The hatching takes approximately 5 minutes. The first larval instar that hatches from the egg is a very tiny animal without visible gills and lives up to 1 m deep in the substrate. In many species also some of the following larval instars have this "subterranean" life-style. Altogether there are 15 to 25 larval instars, depending on the species. Later larval stages can be classed into different life-style types. Most species are benthic and always remain in contact with the substrate ("clinging type"). Some species live interstitial ("crawling type"), hide in the vegetation ("climbing type") or live at least partially digged in the substrate almost like the young larval stages ("digging type"). Some species have larvae that swim in the open water or between water plants ("swimming type"). The types are not strictly separated and the larvae of some species may belong to a different type during earlier and later larval stages. Usually, however, the larval life-style type correlates with the habitat and is also mirrored in a specific morphology of the larvae. Swimming larvae and digging larvae are mostly found in species that live in stagnant or slow-running water. The other types prefer running water habitats. During the early larval stages the animals feed from detritus, bacteria and fungi, in later stages the food source is more species specific. Many species feed from algae or fungi growing on the substrate or water plants, while other species filter food particles from the water. Passively filtering species use the spines on their appendages to filter the water, actively filtering species built special tubes in the substrate and produce a strong water current through these filter tubes with their gills. The last nymphal instar leaves the water and molts into the subimago. The subimago is a fully winged pre-imaginal stage that is able to fly; this is unique in the insects. The subimaginal stage lasts from a couple of hours to several days depending on the species. The molt of the subimago gives rise to the imago. The subimago and the imago do not feed. The imago lives only for a short period of time, usually about 30 hours, but in some cases the imago can live for several days.

DEpository species list

References