Written by Collin McMichael – Program Assistant
Welcome to Bug of the Month! Since it’s now May, the weather is warming up and Texans are beginning to head en masse to the gorgeous rivers of this great state. It only seems appropriate that we would start this column out with an appropriately named, aquatic insect: the mayfly! Mayflies, in the insect order Ephemeroptera, are most commonly encountered as adults with four prominent wings held stiffly out from the body, and often have several tail-like protrusions from their posterior. “Mayflies” is one word instead of “may flies” because they are not true flies, which all belong to the insect order Diptera.
Mayflies are so named because they often have “mass emergences” along rivers in the spring, often in May. When spring rolls around, the mayfly lifestyle undergoes a dramatic shift from aquatic to aerial. The larvae do something wholly unique within the insects: they molt into a life stage known as a sub-imago, the only known non-adult, insect life-stage to be able to fly.
Sub-imagos swarm out of rivers by the thousands on opaque wings, fly up to overhanging branches and molt into their final, clear-winged adult stage. Once they have successfully wriggled out of their final chitinous constraint, a mayfly will fly above the river to form mating clouds with its comrades that are often large enough to show up on weather radar. After mating, mayflies do not live long. Males wither quickly and can form heaps of dead bugs during large emergence events. Females of some species wait to die after laying their eggs while others simply begin to fall apart on the wing, apparently with the hope that their eggs will land safely in the water.
Mayflies are important residents in the rivers of Texas and much of the world. They, along with dragonflies, are among one of the earliest lineages of insect to ever evolve. Mayflies are an important part of a group known as primary consumers, or plant-eaters, that feed the rest of the inhabitants of the waterway. Algae grow on rocks and debris along the river bottom using the light from the sun to power photosynthesis. Mayflies and other primary consumers eat the algae. As these little herbivores scuttle among the muck, they are in turn eaten by fish and other secondary consumers that are in turn eaten by tertiary consumers and so on. This movement of energy through a food chain, or trophic-web, is known as a trophic cascade. Without the transfer of energy up a trophic cascade provides, Texas’ rivers would be devoid of fish, birds, frogs, otters, turtles, and, possibly to some people’s delight, snakes. This makes mayflies and other benthic invertebrates very important aspects of river ecosystems!
Next time you’re out by the river, take a second to look at the bugs around you. Setting up lights near a river around dusk and early evening is a great way to attract mayflies. If you’re lucky you may catch a mass emergence!