Spillover: the powerful, prescient book that predicted the Covid-19 coronavirus pandemic.

by David Quammen

Like an insect, the blacklegged tick undergoes metamorphosis, passing through two immature stages (larva and nymph) on the way to adulthood. At each of those stages, it needs a single blood meal from a vertebrate host to nourish its transmogrification; an adult tick needs another blood meal to supply energy and protein for reproduction. In most cases the vertebrate host is a mammal, though it might also be a lizard, or a ground-nesting bird such as the veery, exposing itself to larval ticks on the forest floor. The blacklegged tick is such a generalist, in fact, that its menu of known hosts includes more than a hundred North American vertebrates, ranging from robins to cows, from squirrels to dogs, from skinks to skunks, from possums to people. “These ticks are unbelievably catholic in their tastes,” Ostfeld told me. An adult female tick spends her winter with a bellyful of blood and then in spring lays her eggs, which hatch into larvae by midsummer. Whether as immatures or as adults, ticks can’t travel very quickly or very far. They don’t fly. They’re not so acrobatic as fleas or springtails. They lumber around like tiny tortoises. But they seem to be “exquisitely sensitive” to chemical and physical signals,45 according to Ostfeld, and thereby “able to orient toward safe locations for overwintering and toward hosts emitting carbon dioxide and infrared radiation.” They smell out their food. They may not be agile, but they’re opportunistic, alert, and ready. The complete li...

The terrific ticks