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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

An autumn sun dance: Mayflies, Ephemeroptera


Beautiful but short lived mayfly adults survive only a matter of days.


No doubt climate change threatens ecosystems around the world, and in what has been one of the warmest years on record in the Mid-Atlantic region Mother Nature has provided unusually warm days well into autumn. Taking advantage of the lingering warmth, I recently took a hike along the stunning Rose River Trail in Shenandoah National Park where I stumbled upon a gang of insects engaged in a curious display of aerial acrobatics near a waterfall. As I watched, small insects swarmed in a vertical column of late afternoon sunlight. Having forgotten to bring along my trusty bug net, I was at a loss to capture one of the acrobats. Fortunately, one exhausted flier ran out of gas and settled on a stone to rest.


Mayfly swarms are a place for the guys and the gals to check each other out and find a mate.

Pristine streams like this one in Shenandoah National Park are excellent breeding sites for mayflies.

Participants of the aerial ballet were mayflies engaged in swarming behavior. Like many other species, mayflies gather in one place to find mates. Mayflies establish mating swarms in physical locations near trees, above boulders, and in clearings and light gaps in the forest. This is the place for males to strut their stuff for females of their species. The ladies assemble in the swarm, check out the guys, see who has the best moves, and seal the deal. Sounds a little like the disco scene with Travolta in Saturday Night Fever, right?  My good fortune on the hike was to happen upon a light gap in the forest canopy that served as the assembly point for this mayfly mating swarm. The revelry of the adult mayfly is short lived for they lack functional mouthparts and cannot feed. Their sole purpose as adults is to find a mate, and for the mated female to find a high quality stream in which to deposit her fertilized eggs.

Mayfly nymphs live the life aquatic and are good indicators of stream quality.


Immature stages of mayflies are called nymphs and they live the life aquatic. After hatching from eggs, nymphs consume aquatic vegetation and detritus (decomposing organic material) found in the streambed. Like their relatives the stoneflies we met in a previous episode, mayfly nymphs can be an indicator species used to gauge the quality of a stream. Many species are intolerant of pollutants. As you might guess, both nymphs and adults are featured items on the menu of many fish, including tasty trout and bass. Anglers have created lures modeled after mayflies with colorful names like Gold-Ribbed Hair’s Ear. In the waning days of autumn take a hike along a mountain stream and pause in a forest light gap. See if you can spot these ephemeral wonders of the insect world.




The interesting article “The mating biology of a mass-swarming mayfly” by J.D. Allan and A.S. Flecker was used to prepare this episode.