What are Mayflies?

Mayflies, also known as shadflies, are aquatic insects belonging to the order Ephemeroptera. They are closely related to, and look somewhat similar to, dragonflies and damselflies. There are over 3000 known species of mayfly, grouped into 42 different families. In their immature, or nymph stage, they live in freshwater areas. Their presence normally indicates a very clean environment.

Mayfly nymphs are normally found living in freshwater streams under rocks or in areas of decaying vegetation. Very few species live in lakes, but those that do are usually found in very large numbers. Most will feed on algae or dead organic material in the water. Some species will feed on the larvae and nymphs of other insects as well.

The Mayfly Life Cycle

Mayflies are born from eggs. The female mayfly can lay anywhere from 400 to 3000 eggs, depending on environmental conditions and the exact species. The eggs are most often dropped onto the surface of the water and allowed to sink down to the bottom. Some species will fly along the water, dipping their abdomen below the surface as they go, dropping a number of eggs each time. Others will stop and stand at the edge of the water depositing their eggs from there. A few species will actually submerge into the water and deposit the eggs among plants or rocks on the bottom, but in general, the eggs are allowed to fall to the bottom on their own. The incubation time for the eggs will vary depending on environmental conditions, with temperature playing a large role. This period can be anywhere from just a few days to close to a full year.

After hatching, the nymphs will burrow their way into sediment. They will remain in this stage for anywhere from several months to several years, again depending on the exact species and environmental conditions. They will molt between 10 and 50 times before reaching maturity. At the end of the nymph stage, there will be a molting process that sees the semi-mature mayfly emerge with wings, but still sexually immature. This is called the subimago stage. Mayflies will emerge in this stage during the spring, summer and autumn months, usually in extremely large numbers.

When the mayfly nymphs reach the subimago stage and are ready to emerge, they will do so in one of several ways. In some species, the transformation occurs under water. The subimago will then make it’s way to the surface and fly into the air. Others will rise to the surface of the water first, shedding their skin and then fly after resting for a few minutes on the shed skin. Other species will make their way out of the water first, undergoing their transformation on land before flying off.

After one or two days, the mayfly will undergo one more molt, becoming fully mature and able to reproduce. The lifespan of an adult mayfly is very short, with some female species only living for a few minutes. At this stage they do not feed, and their only purpose is reproduction.

How to Identify Mayflies

Larvae are typically brown or green and about 1 inch in length. They have no wings and either a flat or cylindrical body. Their color usually blends well with their surroundings. They can have between four and nine sets of gills on the edges of their stomachs, which are normally white, off-white or brown.

Subimago mayflies have wings and resemble their fully mature form. They generally have duller coloring and their wings look hazy. They have tiny hairs all over both their bodies and their wings. They generally stay in this stage for only one or two days.

Adult mayflies have longer limbs and tails, as well as brighter coloring and triangular clear wings, now devoid of hair. They have very large eyes which take up a great portion of their head. Coloring can be black, white, green or yellow.

Signs Of a Mayfly Infestation

Unlike many other pests, a mayfly infestation is not something you will have to look for. If you have a problem with mayflies it will be obvious and you will know it. Although these insects spend most of their lives in or near water, they are attracted to bright lights. If you live near areas of water where mayflies exist, adult mayflies may be attracted to outdoor lights as well as light escaping through windows at night. They do not sting or bite and will not attack humans, but their sheer numbers are a nuisance, and sometimes even frightening. The good news is that adults rarely live for more than a few days and will soon cease to be a problem once they are seen.

For further information you may be interested in these articles:

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