Mayflies are hunted by various carnivorous predators throughout the four stages of their lives. As nymphs, they are preyed upon by fish and carnivorous invertebrates. When they are in their winged stage, their natural predators are flying creatures like birds and bats, as well as predatory insects such as hornets and dragonflies.
When mayflies are at rest, they are preyed upon by birds, spiders, beetles and some mammals. In North America, mayflies are commonly eaten by flying squirrels. As mayflies transition into their adult stage, their common predators are fish, especially when the female is laying eggs. This relationship is why it is common to see artificial fishing lures that are made to look like adult mayflies.
As nymphs, mayflies are entirely aquatic. When they become adults, they live on land. Their lifespan usually only lasts just long enough to mate. During mating, the receptive females fly into large swarms of males, mating while in flight. The female then lays her eggs on the surface of a stream or pond, or on a water-based object.
As their name implies, mayflies are known to emerge from the water in the month of May, often as a collective group. The amount of time spent in the water varies depending on the species, but they live between two weeks and two years before leaving for land.