populace. It was no longer a chimpanzee virus. It had found a new host and adapted, succeeding brilliantly, passing far beyond the horizons of its old existence within chimpanzees. It reached hemophiliacs through the blood supply. It reached drug addicts through shared needles. It reached gay men—reached deeply and catastrophically into their circles of love and acquaintance—by sexual transmission, possibly from an initial contact between two males, an American and a Haitian.
For a dozen years it traveled quietly from person to person. Symptoms were slow to arise. Death lagged some distance behind. No one knew. This virus was patient, unlike Ebola, unlike Marburg. More patient even than rabies, but equally lethal. Somebody gave it to Gaëtan Dugas. Somebody gave it to Randy Shilts. Somebody gave it to a thirty-three-year-old Los Angeles man, who eventually fell ill with pneumonia and a weird oral fungus and, in March 1981, walked into the office of Dr. Michael Gottlieb.
IX
IT DEPENDS
110
Finally, let me tell you a little story about caterpillars. This may seem to take us afield from the origins and perils of zoonotic diseases but, trust me, it’s very germane.
The caterpillar story begins back in 1993. That year, in the tree-shaded town where I live, it seemed that autumn had come early—earlier even than usual for a valley in western Montana, where the cold winds begin blowing in mid-August, the cottonwoods turn color not long after Labor Day, and the first heavy snow often puts a damper on Halloween. This was different. This was June. It seemed like autumn because the leaves were gone from the trees. They had flushed from their buds in May, opening wide and fresh and green; and then, just a month later, they disappeared. They hadn’t succumbed to the natural rhythm of season. They hadn’t turned yellow, fallen, piled up in the gutters as aromatic autumnal mulch. They had been eaten.
A pestilential abundance of small, hairy larvae had materialized like a plague out of Exodus, stripping the trees of their foliage. The Latinate binomial for these voracious leaf-eaters is Malacosoma disstria, though few of us townsfolk knew that at the time. We used another name.
“Tent caterpillars,” said the local newspaper, vaguely but not inaccurately. “Tent caterpillars,” said the city parks people and the agricultural technicians at the county extension service, who were answering calls from dozens of concerned citizens every day. The radio said “tent caterpillars” too. And so before long we were all out on the sidewalks, saying “tent caterpillars!” back and forth to one another. In the hubbub, we were too occupied to notice that these particular “tent caterpillars” didn’t build tents. They just gathered and traveled in dense aggregations, like wildebeests on the Serengeti. Their full common name (their official misnomer?) is the forest tent caterpillar; a closely related insect, the western tent caterpillar (Malacosoma californicum) does build tentlike silken shelters. We weren’t interested in such entomological subtleties. We wanted to know how we could kill the damned things before they ate all our lovely urban hardwoods down to stumps.
It was awesome, in an ugly way. Not every tree was left naked, but many were, especially among the old towering elms and green ashes that stand along the sidewalks, arching their canopies over the neighborhood lanes. It happened fast. The caterpillars did most of their feeding in full daylight or early evening, but later, on those cool June nights, we could stand beneath a great tree and still hear the gentle crackle, like distant brushfire, of their excrement cascading down through the leaves. In the mornings, we would find the sidewalks heavily sprinkled with those poppy-seed globules of dung. Occasionally a lone caterpillar would rappel down on a filament of silk and dangle there mockingly at eye level. On a day of chilly drizzle, too chilly for caterpillar comfort, we could spot them hunkering sociably, high up on a trunk or in a limb crotch, hundreds of fuzzy gray bodies in each pile, like musk oxen huddled against an Arctic storm. Some of us went away for a weekend, leaving the lawn freshly mowed, all seemingly fine, and came home to find that our trees had been defoliated. We climbed up on ladders and sprayed the caterpillars with soapy dishwater from spritzer bottles. We dosed them with bacterial mists or nasty long-molecule chemicals, as variously prescribed by the local garden-store clerks, who knew little more than we did. We called in SWAT-team strikes by the men from Nitro-Green. All of these measures seemed to be marginally