Science of Everyday Life by Jay Ingram

Author:Jay Ingram [Ingram, Jay]
Language: eng
Format: epub
Tags: General, Science, Philosophy & Social Aspects, Science Miscellanea
ISBN: 9780143056638
Publisher: Penguin Group
Published: 2006-07-07T16:25:22.656000+00:00

THE SWARM

It’s dusk on a late-summer day, and there, hovering over the sidewalk in front of you, is a cloud of insects. This cloud, or swarm, is itself almost motionless, although the individual insects are moving ceaselessly up and down, back and forth. What on earth are they doing? The answer is simple: they are there for only one reason—mating.

Swarms are almost always bunches of males who hover together over a prominent landmark waiting for females to show up. Any female who wants to mate finds the swarm, flies up into it, is grabbed by a male, and the two drop to the ground in each other’s clutches. A survey of the sexes caught by the sweep of an insect net through a swarm tells the story: numbers like 700 males and no females or 4,300 males and 22 females are typical. (Presumably those 22 were recent arrivals seeking a male.) Swarming isn’t universal, but tiny insects like gnats, midges and mosquitoes, and the much bigger mayflies (fish-flies) and horseflies all form male-only swarms. Swarms probably make successful mating more likely for both sexes: a tiny, solitary male insect aimlessly cruising around would presumably have little chance of encountering a female, whereas if he’s in a swarm, females can find him. For females, going to the swarm beats scouring the bushes looking for a male. But knowing why male insects form swarms only raises more questions: how do the males choose a place to swarm? What keeps the swarm together? And if you’re one of hundreds of males looking to mate, the old real-estate adage “location, location, location” must come into play: if you’re waiting for a female to arrive, where’s the best place in the swarm to wait?

Swarms are always hovering over something. It can be as simple as a white cloth on the ground or a patio stone. The males position themselves over it, facing into the wind, then fly some simple pattern that keeps them in roughly the same place. Swarms can gather over chimneys, at the tips of tree branches, over telephone poles, steel barrels, cowpies and even human beings. Frederick Knab, an American entomologist writing in 1906, described entering a field where there was a swarm of male mosquitoes over every single corn stalk, and having a swarm form immediately over his head. I saw one in Vancouver hovering over an empty Foster’s Lager can. In 1807 in the German town of Neubrandenburg, an immense swarm formed above the steeple of St Mary’s church, which at the time was being used as a powder magazine. The dark, columnar swarm waving gently in the wind looked so much like smoke that it convinced a number of inhabitants to head for the hills. Only when the “smoke” didn’t spread did someone climb the steeple and discover the truth.

The landmark, whether it’s a beer can or your head, plays a crucial role in allowing the males to hold the swarm together. Instead of having to maintain equal spacing

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