Locust (35 page)

 

When we reached Indian Pass the next morning, Knife Point Glacier lay below us, stretching more than a mile down the windswept valley. The top of the glacier was still covered in a thin crust of snow. Knowing the upper reaches of the glacier were deeply crevassed and that fragile snow bridges may have formed over these gaps, we roped up to descend to where the ice had shed its snowy blanket. Working systematically, Larry and I scoured the upper reaches of the glacier while Charlie and Craig went about their business of collecting water and ice samples and surveying the glacier for comparison to earlier measurements. They had told us that the best places to find insects on their previous trips had been lower on the glacier, but we wanted to carefully inspect as much of the ice as possible. Starting at the top made sense logistically, but not emotionally. The day was a complete bust, except for finding a few scattered moths and wasps that had obviously arrived in recent times.

The next day we worked our way down to an area where the glacier leveled out, just below an immense rock buttress that emerged from the middle of the ice field. It was easy to imagine this outcropping extending under the ice, creating a dam that caused the glacier to cascade in slow motion over the submerged ridge. Within minutes I heard Larry shout. The glacial ice crunched under my crampons as I hurried from the edge of the moraine, where I’d been jotting notes.

As I reached him, I dropped to my hands and knees. The surface of the rotting ice was pockmarked with small pits. In the cavity that he’d marked with the tip of his ice ax lay a crumpled form about an inch long, soaked in meltwater. Its legs were missing but the bulbous head, powerful thorax, tapered abdomen, and straight wings left no doubt that this was the body of a grasshopper—or a locust. In the intense sunlight that cuts through the thin air of 12,000 feet, the soggy black remains had warmed faster than the surrounding ice and the body formed a meltwater pool. The area was littered with bodies. Like a Lilliputian version of the
Night of the Living Dead,
the insect corpses were emerging from their graves.

Larry’s ruddy face split into a grin. He had indeed found the “mother lode,” as we came to call this section of the glacier. He’d stuck with me through August snowstorms, lung-searing climbs, and horrifically bad advice from local guides. The afternoon passed in quiet exuberance as we gently placed the limp and sodden bodies in numbered vials.

The exquisite preservation of so many individuals was a direct result of the mechanism by which this and other glaciers trapped insects. Swarms originating on the western slopes of the Rockies were funneled up the mountain valleys by winds and carried over the passes. A few of these valleys, because of their orientation relative to prevailing winds and their proximity to the habitats where the locusts emerged and aggregated, functioned as thoroughfares during the insectan rush hour (actually a matter of a few days or weeks each year). Some of these montane routes had been carved by glaciers and the rivers associated with their runoff, and in a few cases the ice still persisted at the head of the valley. As the locusts were carried upward, the falling temperature chilled a portion of the swarm, which dropped to the ice, where it was soon immobilized by the cold. In some cases, as the air was funneled through the frigid gaps in the mountains, localized downdrafts and other such perturbations would have forced some of the insects onto the ice.

Based on our findings, the insects must have been interred in huge numbers. We hypothesized that they had been washed by summer meltwater into the crevasses some 300 yards above us. This initial
process had not been possible in the glaciers that we had studied in previous years, as these bodies of ice generally lacked the size and topographic variation to form numerous crevasses (except for the third Grasshopper Glacier, and perhaps well-preserved insects will be the reward if and when someone finally accesses the main body of ice). As the ice flowed down the mountain, the crevasses closed and entombed their contents. The frozen creatures were carried over the ice fall formed by the rock outcropping above us and were then brought to the surface by the turbulent flow at the base of the cascade. It was like casting a fishing lure in the still water above a log dam, allowing it to be swept over the waterfall, and then seeing it bob to the surface in the churning water below the cascade.

Charlie and Craig had determined from their work that the glacier was flowing at about six and a half feet per year. So, if our inferences were correct, it should have taken about 150 years for the bodies to travel the 300 yards from the crevasses to where they were found. Months later, our radiocarbon dating placed the time of deposition between 100 and 200 years ago. Given the remarkable sequence of events that ensured both the preservation of the bodies deep within the ice and their return to the surface, perhaps it was not surprising that we’d failed to find well-preserved remains until now.

The thigh-burning trudge back up the glacier, over the pass, and back down to camp at the end of the day was as grueling as ever, but the pain felt strangely good. That night, as Larry brought water up from the stream and Craig and Charlie fixed a dinner of rehydrated jumbo shrimp on a bed of rice (an absurdly decadent meal that they’d snuck into the food boxes in anticipation of a celebration), I dissected one of the few males that we’d collected. Tearing into the body would destroy the integrity of this rare and valuable specimen, but I had to know what we had found. By the hissing, white light of a Coleman lantern, I teased apart the abdomen. The hardened cingula and epiphallus clung weakly to the soft, decomposing tissues within the shriveled abdomen. These were the surviving structures of the internal genitalia, the feature that Theodore Hubbell had found to be so
powerfully informative decades earlier. A field microscope provided enough magnification to eliminate any doubt. We’d found the Rocky Mountain locust.

After dinner, I took the dishes down to the stream for washing. Usually, my job was cooking, but tonight I’d begged off in order to conduct my dissection and ensure that our celebration was in order. Scrubbing the plates by moonlight was peaceful. My hands were soon numb in the icy water, which soothed the cuts and scrapes that had come from working on the jagged ice.

 

Over the next few days, we collected 250 bodies from Knife Point Glacier and Bull Lake Glacier, an adjacent body of ice separated by a shared lateral moraine. Many were too crushed or dismembered for definitive identification, but about 100 had the distinct thoracic spine that gave the subfamily its common name of “spurthroated” grasshoppers. Amid these, there were 14 males with well-preserved abdomens and genitalia, all of which were unambiguously the Rocky Mountain locust.

In the months leading up to our expedition, Larry had invented the “locust body bag,” a contraption for concentrating insect remains embedded in blocks of ice. The device had a folding aluminum frame that supported a thick, black plastic bag—very much like a five-gallon body bag—in which a block of frozen remains was placed. The bag was then sealed and the apparatus set on a sunny rock, so the intense sunlight would heat the bag and melt the ice. A few small holes in the bottom of the bag allowed the meltwater to drain out, and in just a couple of hours the contents were reduced to a soggy mass of jumbled body parts. With his simple invention, we reduced five-pound blocks of frozen detritus to a few ounces of valuable specimens (DNA and the other diagnostic biochemicals are fairly stable for short periods, and we kept a small portion of the samples frozen just to be sure). Although everyone carried their maximum load back to camp each afternoon, Larry’s strength and fortitude made him the human pack-horse at the end of the day. So nobody was more pleased than he with the effectiveness of the “locust body bag” during the 1,300-foot climb back up and over Indian Pass.

Based on our collections, the sex ratio of the swarms was markedly biased toward females, which outnumbered males by slightly more than three to one. Nowhere in Riley’s studies was this preponderance of females noted. I speculated that this phenomenon might have been characteristic of freshly emerging swarms in the Rockies. If swarming was a survival strategy for
spretus,
then it makes sense that females would comprise more of the migrants. Let’s face it, if we were sending a rocket into space to establish a colony on a distant planet, it would make a lot more sense to stack the manifest with female colonists. We also know that when swarms of other locust species proceed across the landscape they become increasingly dominated by males, as mature females drop out of the migration to lay eggs. So, perhaps a newly forming swarm—such as would have been blown onto the glacier—would be biased toward females to compensate for their loss on the journey.

As the sun melted the blanket of snow covering the upper reaches of the glacier, a most remarkable pattern was revealed in the ice. Hundreds of parallel, curved lines stretched across the width of the glacier. Like growth rings in a tree trunk, these darkened bands marked annual deposits. Each winter, the snow created a fresh layer on the glacier, and during the short summer that followed, dust, pollen, and insects would form a thin organic layer on top. This two-toned annual deposit would then be slowly incorporated into the surface of the glacier, creating a distinct record of the year’s events. Trekking up this stratified section of the glacier was like walking along the edge of a gargantuan stack of plates, with the newest plates at the top of the stack. By carefully inspecting each of the darkened bands, we were able to determine the time line of locust deposits on the glacier. These strata did not include whole bodies of locusts, but there were plenty of legs and mandibles. And with Scott’s forensic method for identifying mandibles, we were able to determine that all but one of the strata contained the remnants of
spretus
. The only other deposit was, not surprisingly, composed of the remains of
sanguinipes
.

We meticulously sampled a continuous series of bands, representing three centuries of history. Of course, not every stratum had locust remains. From Riley’s reports we knew that the average interval between
outbreaks of the locust across the Rocky Mountain states was six and half years, with a rather wide variance. The average number of bands between those that contained locusts was six and three-quarters, a remarkable match. It seemed that the glacier provided an incredibly effective and accurate record of major outbreaks. Given that the outbreaks originated in the lands just to the northwest of these glaciated peaks and that the prevailing winds were from this direction, perhaps it is not altogether surprising that the glacier managed to trap a sample of the passing swarms during each of the plagues.

These findings meant that the pattern of locust outbreaks that was documented in the mid-nineteenth century had been ongoing for at least 300 years. Changes wrought by European settlers were not the cause of, and did not increase the frequency of, locust outbreaks. Our analysis also revealed that the temporal pattern of locust remains was random. There were no apparent cycles or regularities in the distribution of swarms. A similar lack of pattern was found when we analyzed Riley’s records of locust outbreaks. If outbreaks of the Rocky Mountain locust were driven by the weather, then randomness made sense; within a span of a few centuries, the occurrence of mid-continental droughts is highly irregular.

On the next body of ice beyond Bull Lake Glacier, Larry found no insect remains but plenty of evidence that another scientific expedition had recently passed through. Indeed, just a few weeks earlier, a team from the U.S. Geological Survey—Hayden’s old outfit—had taken ice cores from Upper Fremont Glacier to study its history and predict its fate. Through Craig and Charlie’s connections we contacted the federal scientists and let them know of our study. Months later, they sent me a single tibia that they’d extracted from a core 315 feet below the surface. I determined that it was the leg of a grasshopper or locust, and after radiocarbon dating it became the oldest evidence of what we assume was a locust outbreak in North America. When this swarm of Rocky Mountain locusts was preparing to sweep across the Great Plains in the twelfth century, Genghis Khan and his Mongol army were sweeping across the steppes of Asia.

On the last day on the ice, we set up a drift net in one of the rivulets pouring down the face of the glacier. A drift net is commonly used to
sample stream insects. It comprises a metal frame that is anchored to the substrate, in our case by means of ice screws. Attached to the frame is a long, fine-mesh net through which the water flows. Whatever is drifting in the current is caught in the net, and the flow of the water prevents it from being washed back out or otherwise escaping. By extrapolating from our sample catch, we estimated that the remains of at least 4 million locusts were washing out of the glacier during a typical summer’s melting. And according to Charlie and Craig, the terminus of the glacier had receded 250 yards since 1963.

A vast storehouse of biological specimens, representing centuries of natural history that could only be viewed through this window of ice, was being flushed down the valley. Perhaps a small portion of the lighter fragments would make their way into the Wind River and be carried into the agricultural fields along with irrigation water. I like to imagine that the Rocky Mountain locust might in this way return to the crops of the western farmers, completing its centuries-long journey, but taking nothing from the verdant fields. If not thanked for providing a bit of humus to the soil, at least its arrival is no longer cursed.

In recent years the rate of melting apparently has accelerated so that immense mounds of decomposing bodies have begun to pile up alongside the receding ice. According to Jonathan Ratner, an environmental consultant and avid hiker in the Wind River Range, hundreds of acres were covered in two to six inches of the rotting peat-moss-like remains of locusts in the summer of 2002. Based on our back-of-the-envelope estimates, the heaps of material included 20,000 cubic yards of corpses, enough to fill 1,200 dump trucks.