Hunger on the Wing (Part 1 of 3)

An African sky filled with locusts
Here's another story from The Book of Deadly Animals. (Thenew US paperback version hits book store shelves tomorrow; or order it onlinehere.) In the book, I didn't have room for the whole story, since there weremore than 900 other animals to talk about. This longer version first appearedin Discover.

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One summer in the Oklahoma panhandle the grasshoppers wereeverywhere. Every patch of weeds along the alley would erupt like a pan ofpopping corn if I set foot in it. When we drove the highway, we inadvertently slaughtereddozens. The collisions speckled our windshield with hemolymph. Their wings,coffee-colored fans striped with yellow at the outer edges, lodged in ourwipers and fluttered in the onrushing air. Sometimes an entire grasshopper, ormost of one, would lodge there as well, struggling to get free as the wind toreit to tatters.
They could be found in unaccustomed places that summer. Forseveral mornings running I saw two or three swimming in the dog's water dish.The rosebushes took on the riddled look of lace, as though the grasshoppers hadtasted the leaves and found them unappealing but serviceable. In the country,the cedar posts of barbed wire fences would seem at a glance to be shimmeringwith heat, like a water mirage on the highway, but a second glance would showthe effect was not an optical illusion. The posts were simply crawling withgrasshoppers moving up or down for no apparent reason. They seemed to be movingwith great caution, edging past each other. When a stationary grasshopper got bumped,it would draw its legs in tighter and shift its footing, like a personuncomfortable on a crowded bus.
Then there was the jackrabbit. We found it beside a dirtroad on the way to the mailbox. It was dead, probably road-killed. Grasshopperswere thick in the weeds and grass along that road, and dozens clustered on thecarcass. When someone poked at it experimentally, a few of the hoppers jumpedoff and opened their wings and were carried away by the wind. Others crawledoff sluggishly. Some stayed put. With the carcass now more exposed, we couldsee that it was bald in patches, and that its hide was wounded in shallowdivots, as if it had been hit all over with buckshot that failed to penetrate.It seemed that the grasshoppers had been eating it.
As the season wore on, the grasshoppers grew absurdly thick.Among the metallic green ones there were others, some yellow and spotted,others a brighter green. All these I was familiar with, though I had never madeany particular study of them. But I began to see things utterly new to me. Onegrasshopper was black and flecked with gray, like burned charcoal. Another wasblack but flecked with a Tabasco red. This variety has been explained to methus: In outbreaks, grasshoppers are so plentiful that they overwhelm theirusual predators, offering them more food than they can use. Other grasshopperspecies, rare enough to go unnoticed most of the time, get relief frompredators in this circumstance, and therefore are more likely to be around forpeople to notice.
Other things seemed different too—there were a great manylarge grasshoppers, thick as a lipstick. One morning on my driveway I found thelargest specimen I had ever seen, a yellowish creature longer than a soda can.It was dead—a fact that gave me some comfort. Streams of black ants led up toits carcass. Their presence was the first thing that convinced me I was seeinga once-living creature rather than a toy. I turned it belly-up with a stick.Its head and thorax were intact, but its abdomen was riddled with holes. I hadnot seen this damage at first because its long wings concealed it from above.Through the holes I glimpsed ants working at the grasshopper's half-hollowhull.
What I've been describing is an infestation, a localizedpopulation suddenly grown orders of magnitude beyond its usual numbers. Thecauses are not thoroughly understood. In the United States, hot, dry weatherhas something to do with it—the heat lets grasshoppers grow faster, and thedryness discourages the fungi that would otherwise check the population'sgrowth.
Swarms of locusts—giant flying species of grasshoppers—are atraveling variation on this phenomenon. They dominate a wide swath of this planetalmost every year. Moving in groups of millions, the locusts migrate over greatstretches of territory, settling down periodically to eat every bit ofvegetable matter in sight. They are hunger on the wing.

In the United States migratory swarms of locusts arepresumed to be a thing of the past. But a locust is really just an oversizegrasshopper in a gregarious mood. When grasshoppers of certain species gatherin great numbers, they begin to change their behavior. Normally, they aresomewhat solitary. If forced together they seem uncomfortable, leaping awayfrom each other. But hunger often forces them together when a bumper crop ofgrasshoppers encounters a meager supply of food and they must compete for it.If the crowding persists, the younger insects begin to change. The changes varywith the species, but in general their bodies grow to massive size. Their wingsbecome clear and strong. Their colors shift dramatically—for example, fromgreen and yellow to solid black. Their proportions alter, their shapeessentially changing to accommodate flight. So profound is this change that scientistsin the past have mislabeled the two phases, solitary and gregarious, asdistinct species.
The creatures behave differently, too. They eat withshocking voracity. They whirl into the air in groups, forming swarm clouds. Theswarms fly long distances, disrupting ecosystems for hundreds of miles. In the1870s, one swarm was tracked from Montana to Texas, a distance of 1,500 miles.Polluted layers of glaciers high in the Rockies show that their flightsometimes takes them to altitudes beyond the normal range of grasshoppers. In1874 a Nebraska doctor used telegraphs to find the far edges of a swarm heobserved flying overhead, establishing that its area exceeded that of Colorado.Factoring in their rate and the depth of the swarm cloud, he arrived at anestimate of 12.5 trillion grasshoppers. The Guinness Book of World Records liststhis swarm as the "Greatest Concentration of Animals" yet observed.More rigorous methods were used on a swarm in Kenya in 1954, yielding thefigure of 10 billion grasshoppers in a swarm, which happened to be only one of50 swarms in that country at the time.