Gnat Swarms: Investigating their Constant Radius and Mating Habits

[JoAuSc]

I was out in the woods today and I noticed a cloud of gnats swarming about a fixed point, seemingly random but maintaining a roughly spherical shape of a certain radius.

Why is it that this swarm maintained a cloud of roughly constant size rather than shrinking or growing? Also, what is it that gnats do in swarms like these? (Wikipedia mentions mating swarms, but it would help if I knew why they decide to mate in the air, or who's chasing who.)

 

[jim mcnamara]

gnats is a generic term for several groups of bugs, all are two-winged flies.

A lot of the males of the various species depend on pheromones secreted by sexually receptive females to find those females. When a female or a group of females becomes receptive, the males flock in from hundreds of yards away and gather around the females.

You end up with a ball of almost all male flies. The reason the ball size stays the same is that the males are responding to the concentration of pheromone - as they buzz around and move away from the source, they correct course and zoom back toward the greatest concentration of pheromone - ie., the female. As a guess: the response time of their pheromone 'radar' and their velocity dictates the size of the ball. Better response time = smaller ball, greater velocity = bigger ball.

Mating balls are common in mosquitoes; they look more like a vortex than a true sphere. You can see them over swampy areas during the day - look across the swamp toward a low angle sun so the mosquitoes are backlit. You'll see lots of them.

Reason for the balls: the males are trying to be the one that mates with the female. She can be very picky. A majority of true fly species mate on solid surfaces, not in flight