(An expanded version of a story from The Book of Deadly Animals. Go to the beginning of this story.)
One afternoon I looked in on the six or seven grasshoppers I had in separate jars and found that they had done something interesting. Wet orange strands, about the thickness and texture of a braided bootlace, lay in their jars. A day or two later, I saw one of my captives in the act of producing such a strand. It pressed its hind end against the floor of the jar and arched its back, as if exerting downward pressure, and an orange strand squeezed out from the rear, like toothpaste from a tube. This strand looked slimier and smoother than the others I'd seen but was recognizably the same thing. By the next day it had dried to look exactly like the other hoppers' strands, the pattern of its texture emerging as it dried. A day later it was dry enough to see that what had appeared to be individual strands woven together were merely dozens of pieces, shaped like sesame seeds, arranged in an orderly overlap—eggs, of course.
In Missouri in the 1870s, the egg masses of Rocky Mountain locusts lay so thick in the beds of rivers and creeks that authorities offered a five-dollar bounty per bushel of them. This species, the only grasshopper in North America that typically shifted into the locust phase, had swarmed for hundreds of years, as proved by layers of locusts in glaciers dated at around 750 years old. Presumably, they had swarmed for millennia before that. But around 1880 the swarms abruptly ceased, and the species went extinct. The last live specimens were collected in 1902.
No one knows why the Rocky Mountain grasshopper vanished, but changes in habitat are the most likely reason. In the late 19th century, the bison was virtually exterminated, as were the native peoples. Settlers drastically reduced the numbers of beaver in the Rocky Mountains, removing an important control on flooding. Cattle brought in by ranchers grazed and trampled the riversides, and farmers plowed up their fertile soil. To fight off the locusts, farmers tried all sorts of control measures, from contraptions called "hopperdozers" and controlled fires to fasting and prayer. What actually worked was to carry on farming. Plowing devastated the Rocky Mountain locust population, as did the planting of exotic trees, which brought in many new predatory birds.
Hundreds of other grasshopper species thrived despite, or even because of, these habitat changes. But according to Jeff Lockwood, an entomologist at the University of Wyoming, the Rocky Mountain grasshopper's nesting habits made it particularly vulnerable. (Many species prefer grassy hillsides for nesting sites.) The Rocky Mountain locust's boom-and-bust population cycles also put it at risk. Despite the vast areas attacked by swarms—from Manitoba to Texas and from Wisconsin almost to the West Coast—the locust's home base, the area where it could always be found in plague years as well as other times, was a much smaller area in the northern Rockies. European-American settlement there quickly dispatched the species. It's the only known case of a pest species exterminated by human action, and it was an accident.
The extinction went unnoticed for a few decades—that such a fecund creature could abruptly vanish was counterintuitive—and unmourned. The focus of 19th-century science was killing pests, not appreciating them. We still don't know what effect the extinction has had. The swarms caused widespread nutrient recycling and large-scale habitat disruption. Charles Bomar, an insect ecologist at the University of Wisconsin at Stout, has speculated that they served as some sort of cyclic ground clearing, much like forest fires. But specific effects are difficult to substantiate, and no one has proved any related extinctions.
Even the basic facts are in dispute. Daniel Otte, the curator of entomology at the Academy of Natural Sciences in Philadelphia, suggests the Rocky Mountain locust is not extinct at all but has simply refrained from swarming in recent times, perhaps because of encroaching agriculture. Otte points out that almost no one can distinguish closely related grasshopper species by sight. In fact, the integrity of the Rocky Mountain locust, Melanoplus spretus, as a distinct species has only recently been demonstrated through genetic analysis. The characteristics that distinguish M. spretus from its close, and still living, cousin Melanoplus sanguinipes (the migratory grasshopper) are its proportions. Identifying an M. spretus involves taking its measurements—the length of the various leg segments, for example—and comparing them with published figures derived from statistical analysis. To complicate this problem, no one is sure what the solitary phase of M. spretus looked like. The very idea of grasshoppers shifting phases came about just as M. spretus was dying out. It's possible, Otte says, that Rocky Mountain locusts are nibbling at your lawn right now, unrecognized. More likely, they're hidden in remote river valleys, reduced in number but still thriving.
This apparent extinction, far from creating a domino effect of further losses, may have created an opportunity for other grasshopper species. The red-legged grasshopper (Melanoplus femurrubrum), which was responsible for newsworthy outbreaks in Idaho in 2001, thrives on ground broken by agriculture and other human endeavors. Its numbers have grown much larger since the extinction of its cousin. In 2002, patchy outbreaks of clear-winged grasshoppers (Camnulla pellucida) in Colorado attained densities of 200 per square yard; a tenth of this number is considered a danger to crops. Scientists have had some success in developing toxins and parasite-laden baits to combat grasshopper outbreaks. But applying pesticides on broad stretches of land has rarely proved cost-effective. Some pesticides seem to make future outbreaks worse, because the predator and parasite populations they affect don't recover from the poisoning as fast as the grasshoppers do.
Even though existing North American grasshopper species don't migrate as readily as the Rocky Mountain locust did, some of them do swarm in less dramatic migrations. And their swarming potential may have more to do with circumstances than with any inherent limitations. Bomar suggests these other species, especially the red-legged grasshopper and the migratory grasshopper, are stepping into the niche the Rocky Mountain locust vacated. His suggestion brings back uncomfortable memories of the giant I found in my driveway. "The potential for swarms is there," Bomar says. "Eventually, one of these micropopulations is going to move out." He's intrigued by the scientific opportunity such an event would present. For the rest of us, it may be the return of an ancestral nightmare.
|African locusts herded into a trap|
|A pitful awaiting immolation|