Mayflies in July

(This column was first published in the July 21, 1997 Buffalo News.)

   At a Buffalo Bison baseball game one evening last week (another win) the air was suddenly saturated with Mayflies. I could look up and see hundreds of them flying in the stadium lights silhouetted against the dark sky. Fluttering slowly, they were easy to identify.

   Although there are minor variations among the over 200 Mayfly species in this region, the narrow bodies of most are about an inch long with two tails extending from the end of their abdomen for an additional inch. Their forelegs are long too and are held forward when they alight.

   Later enroute home on the subway I noticed one perched like a stick pin on the blouse of a young woman standing next to me. After I pointed it out to her, she in turn showed me that one stood on my neck. So delicate was it that I had not even felt it.

   Mayflies in mid-July? This was one more indication of how unseasonably late our spring has been. In some years these insects even appear in April when they are referred to by an alternate name, shadflies.

   Despite those two names, these are not flies at all. True flies have a single pair of wings, Mayflies two pairs. Mayflies belong to an order all their own, Ephemeroptera, a name that means ephemeral wings. Indeed the winged stages of this unusual insect are very brief. As adults they survive only a day or two, some only hours. They can't even eat: they have no mouths. During this brief life their sole function is to mate and the females to lay eggs. Nature has conditioned them to mature all at the same time so that these processes can be carried out effectively. Thus they arrive in huge swarms or what entomologists call "blooms."

   The appearance of those insects in this region is not at all unusual. I recall once driving across the Rainbow Bridge in Niagara Falls in a cloud of Mayflies so dense that the bridge lights appeared dim. It was just like driving in a thick fog. Before I could slow down my windshield was covered with squashed insects and I could feel the car begin to lose traction on masses of their slippery bodies. At the end of the bridge I had to stop to clear the car windows, yet a short distance from the river no more Mayflies were to be seen.

   Like many area cottagers I have also witnessed windrows of their fetid dead bodies along Lake Erie beaches.

   Those eggs that are deposited in the water will hatch in a few weeks, but the nymphs or naiads they produce -- wingless but also with two tails -- will live on the bottom of the river or lake for a year or two before emerging. During that time they will eat underwater vegetation and sometimes other insects and many will molt over 20 times as they increase in size. Finally in another spring they will transform into subadults with wings and leave the water to dry. (Among all insects these are the only winged immatures.) After a day or two they will molt a final time into adults and another bloom will occur.
 Mayflies are near the bottom of the food chain and form an important part of fish diet. Those who tie flies for fishing know these insects well and many of their lures mimic them.

   Although they can be a brief nuisance in the spring, we should welcome these harmless insects. They are especially sensitive to pollution and their reappearance in such numbers hopefully signals continued water quality improvement.