Insect external structure
Insect internal structure
Development of insects
Relationships of insects
May fly picture
Insect identification > Ephemerida > May flies
May flies are most abundant near streams and lakes, as their nymphs live in the water. The fully mature nymphs leave the water, usually in greatest numbers about sunset, and, suddenly molting, extend their wings and fly off but, as above stated, usually molt again within a few hours. As their flight generally begins about dusk and as they are strongly attracted to lights, they are often seen in multitudes around street lights during the evenings.
The adults live only a few hours - not more than a few days at most - but during this time the eggs are laid in the water. The nymphs which hatch from them feed mainly on vegetable matter at the bottom, though some are possibly partly carnivorous. They live for one, two or three years, according to the species concerned (some have two generations each year), feeding, and molting with unusual frequency for insects (Lubbock observed 21 molts in one species), until they are full-grown. During this time the mouth-parts are well developed and of the chewing type, but in the adult they become practically useless.
These insects are of no economic importance except perhaps to a very slight degree as scavengers in the water, feeding on matter that might otherwise decay and become objectionable, but their value for this is probably small at best. They are fed upon as larvae, and to some extent as adults, by fish and some carnivorous insects of other groups and for this reason also may be rated as slightly beneficial. At present about eight hundred kinds are known (Austin), but the group has not been very thoroughly studied. Many fossil ephemerids have been found, which suggests that the insects are possibly less abundant now than was once the case.