Last week on a welcomed warm afternoon, swarms of small flies bobbed and weaved over the lawn in my backyard. These small flies, roughly 8 millimeters long, were March flies. In many parts of the land, March flies make an appearance in April or May rather than March, creating an interesting misnomer for these small flies. As a family of insects, March flies include the curious Lovebugs we met in our Valentine’s Day episode back in February.
Swarms of March flies dance in my backyard on welcomed warm days in April.
Since last growing season March fly larvae have been consuming organic matter in the soil beneath my lawn. These tiny maggots are recyclers helping unlock the nutrients in decomposing plants and returning them to the food web that is my backyard. Several weeks ago they completed development and formed pupae which, with the warmth of spring, soon produced the acrobatic flies performing over my zoysia grass.
The aerial ballet performed by March flies consists mostly of males jockeying for position to capture a mate as female March flies emerge from the turf. Bobbing, weaving, chasing other males, and intercepting females in flight are facilitated by the large complex eyes of the males. These bulbous eyes are actually divided into dorsal and ventral visual systems with the dorsal eyes gathering information from above and the ventral eyes watching what lies below – truly a case of four eyes. However, clever photographic analysis has shown that the dorsal eyes are the ones used to gage pursuit of other March flies and to differentiate potential mates from potential competing suitors. One fascinating study of male swarming behavior discovered that larger males often occupied flight space nearer the ground where they chased other smaller males away - all the better to intercept nubile females as they rose from the earth. After mating, females will return to the soil and lay more than 100 eggs to complete the circle of life.
After a respite on a blade of grass, this male March fly rises to stake his claim of airspace in the mating game.
In addition to being highly entertaining as they swarm in my yard, many March flies are important pollinators of spring blooming plants. Soon my large holly tree will give forth with blossoms and March flies will join the wild menagerie of bees, wasps, and other flies vying for nectar.
The interesting article “Sexual Dimorphism in the Visual System of Flies: The Free Flight Behaviour of Male Bibionidae (Diptera)”, by Jochen Zeil, was used as a reference for this episode.