科学美国人60秒:Insects Forgo Flocks in Favor of Swarms

Aha—got ‘im! Yes, the mosquitos are swarming this time of year. Alaskans joke that the bloodsucker is their state bird. But have you ever looked closely at a swarm of mating mosquitos, gnats, or midges? It’s a curious thing. The swarm maintains a kind of shape as it moves around. But the bugs inside it seem to flit about randomly rather than flocking like birds.

This collective, yet disordered, flight intrigued physicists in Rome. They shot ultraslow-motion video of swarming midges. Then they mapped the flight of each midge, and did a mathematical analysis of the collective behavior.

Their finding: the motion of the midges is not random. The bugs stay far enough apart to avoid locking into a formation. The swarm instead expands as needed to stay just below the threshold density. The work appears on the site arXiv.org. [Alessandro Attanasi et al., Wild swarms of midges linger at the edge of an ordering phase transition]

Flocks and schools move in formation only once the group reaches a critical density.  Below that threshold, the individuals move—well, like midges. Insect avoidance of full-fledged flocking may be a reproductive strategy: after all, it’s hard to mingle when you’re stuck in a line dance.

—Wayt Gibbs