Nature Note - Mayflies

Look for mayflies by the porchlight. Image:

Leave an outside light on during a summer night and you're likely to eventually find one or two large insects with two long appendages at their back sitting placidly by the light. These are mayflies, members of the order Ephemeroptera. The Latin name comes from the short amount of time, a day at most, each flying insect lives. There are over 3,000 species of mayflies worldwide, and a 2011 paper documented 131 species of mayflies in the Adirondack Park alone.

Though flying mayflies are short-lived, they do live for a year or so underwater as larvae. The larvae can easily be found by flipping rocks in clean running streams and looking closely for scurrying shapes. The number and type of different mayflies, along with stoneflies and caddisflies, are used to assess the water quality of rivers and streams. Once the larvae hatch into adults they emerge from the water for only a day or so to mate and die. Hatches happen en masse filling the air with flying insects, all looking for love.  A mayfly hatch on the Mississippi in Wisconsin in 2014 was so big that it was visible to weather radar.

Hatches lead to feeding frenzies by trout and other fish, as well as bats and insectivorous birds. Fly fishermen try to match the hatch with their lures. Yet, by all hatching at one time, the insects overwhelm potential predators and ensure that at least some of the individuals successfully reproduce. Hatches also provide a means of dispersal for the insects. They may move away from the waters in which they were born to colonize new waterbodies. This is one mechanism by which insects that get swept downstream in floods manage to reestablish populations in headwaters.

A recent paper showed differences in how far aquatic insects travel when they hatch from streams adjacent to forested versus agricultural land. In traps along agricultural streams, the researchers found more insects, but only close to the streams. Along forested streams, aquatic insects were less abundant, but more evenly distributed between traps set at different distances from the streams. The researchers pointed out that this means any food value the insects might have, in the form of carbon or other nutrients, does not move far from the water in agricultural landscapes.