Behavior And Reproduction

Mayfly larvae are important in transferring energy in freshwater habitats. The larvae strain and eat large amounts of algae as food. They transfer the algae's energy to other animals when fishes, birds, insects, and spiders eat them.

Most larvae remain hidden during the day to avoid predators (PREH-duh-ters), or animals who hunt them for food, but others are found swimming out in the open in the daytime. Some species live in groups, especially in puddles and pools that last for only a short period of time. They usually come out of the water at dawn or just before nightfall to transform into adults, but some species leave the water at midday. Males usually surface well before the females.

Adult male mayflies sometimes take part in massive mating flights. The time, location, flight pattern, and number of participating mayflies vary with each species. Some swarms are composed of a few males, and others have hundreds or even thousands of mayflies. Females fly above the swarms and are spotted by the males swarming below. Males use their long front legs to grab the females. Sperm is transferred to the female directly. After mating, the female lays one hundred to twelve hundred eggs in the water.

Mayflies spend most of their lives in the water as eggs and larvae. The eggs take one week to one year to hatch. In most species the larvae molt, or shed their external skeletons, fifteen to twenty-five times before reaching adulthood. Depending on the species and local conditions, such as temperature and wa


More than one hundred years ago many European rivers were the sites of spectacular swarms of mayflies numbering in the thousands every year. Since then, many populations have declined drastically or disappeared entirely. Scientists blame water pollution and larval habitat destruction caused by heavy industries located on the rivers. As factories in Communist countries started closing in the early 1990s, the water quality of many rivers in Eastern Europe began to improve, giving some mayfly populations a chance to increase their numbers.

ter quality, mayfly larvae take from three weeks to three years to reach adulthood.

Mayflies are the only order of insects that has an extra winged stage called the "subimago" (sub-ih-MAH-goh) The subimago is duller in color than the adult, or imago. It is also heavier bodied and has wings that are smoky instead of clear. The subimago is covered with water-repellent hairs that allow it to emerge from the water unharmed in preparation for adult life on land. At this stage, the mayfly has lost its larval gills and would be in danger of drowning as it makes its way to the surface, if it were not for the hairs, which keep water away from the mayfly's breathing holes. The adults live only a few days, just long enough to mate and lay eggs.

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