Midge Swarms

midges

Left: Swarm of midges hovers near a bush on Lake Michigan
Right: A male midge had dropped from the swarm and poses on a leaf

Spring in Indiana brings swarms of midges. Generally, they are of little nuisance but noticeable as small clouds of rapidly moving insects. The insects in the swarm are all males. The swarm is maintained by an aggregation pheromone released by males. The odor is strongest near the center of the swarm. When an individual strays from the swarm, the pheromone concentration drops and the individual will reverse course, a behavior that leads back to the swarm.

Swarms make small insects like midges detectable, especially from a distance. Swarm visibility is important for insects of small size and low density to attract mates in a complex environment. Males find mates in swarms. Individuals not in a swarm rarely if ever successfully mate. Life in the swarm means that males must compete with each other for mates. This selects for size, agility and ability to detect mates. Males in smaller swarms have less competition and better odds of mating than males in larger swarms. However, male in small swarms are more likely to be eaten by predators. Thus predation pushes the size of swarms above a minimum size that increases the odds of survival. Mating success rates push the size of swarms below a maximum that increases chances of mating. The factors governing size and location of swarms are complex.

About jjneal

Jonathan Neal is a retired Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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