On my road trip to Michigan there were surprisingly (pleasantly) few mosquitoes. However, swarms of chironomid midges were common. The swarms are the male midges congregating into a large mass that attracts females. The males release a pheromone that attracts males as well as females. If a male senses a drop in the pheromone odor, it will turn toward the pheromone cloud until it rejoins to the swarm. The pheromone helps organize the swarm and keep it intact.
The males have plumose (many branched) antennae. The many branches increase the surface area available for male pheromone receptors. Occasionally, males will drop out of the swarm, rest on nearby foliage and pose for photographs. Unlike mosquitoes, these midges are harmless and do not bite.
All the males in the swarm face the same direction, downwind. As the pheromone blows downwind, it will attract females who follow the wind to the mating swarm. There is competition among the males to be first to court a newly arriving female. Thus, they all intently face downwind waiting for a mate to arrive.
The midges must be strong fliers to maintain their position on windy days. It is fascinating to watch the swarm be buffeted about from side to side while the males manage to hold their relative positions.
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
