When the Sky Attacks Itself

There is footage of a locust swarm meeting a hailstorm mid-air, and the physics of it plays out exactly as you'd fear. The insects, which had been moving as a single dark organism across the sky, are struck by falling ice and drop out of formation in the thousands, pattering down alongside the hailstones like a second, wingèd precipitation.

Two of the more dramatic things weather and biology can produce, colliding, cancelling.

Locust swarms are among the largest animal aggregations ever recorded. A single desert locust swarm can cover several hundred square kilometres and pack roughly 80 million insects into each square kilometre. The largest documented swarm, over the western United States in 1875, was estimated at 12.5 trillion Rocky Mountain locusts — a mass of insects covering an area larger than California. (That species then went extinct within thirty years, one of the stranger disappearances in entomology; nobody is entirely sure why, though the ploughing of their riverbank breeding grounds is the leading suspect.)

What makes a locust a locust rather than a regular grasshopper is a switch. Under crowded conditions, brushing against each other repeatedly on the hind legs, solitary grasshoppers undergo what's called phase change: they alter colour, grow different bodies, and begin behaving as a collective. Serotonin drives the transformation. A shy insect, touched enough times by its neighbours, becomes part of a plague.

Which is where the collision gets interesting. Locusts are cold-blooded and need warmth to fly. A hailstorm is a column of air violent enough to keep chunks of ice suspended aloft until they grow heavy enough to fall — sometimes to golf-ball size, sometimes larger. A flying insect caught in that updraft has no chance. Chilled, battered, and grounded, the swarm simply comes apart.

The Book of Exodus lists locusts as the eighth plague and hail as the seventh. In the sequence there they arrive back to back, hail then locusts, one after the other. Watch the footage and they arrive together instead — the seventh plague dismantling the eighth in the same patch of sky, one disaster doing the work of erasing another. The weather, for once, on the crops' side.