back to camp. We agreed that we would return to the same spot the next
day to try to catch the ant-bird-butterfly procession.
IN the late nineteen-seventies, an entomologist named Terry Erwin
was working in Panama when someone asked him how many species of
insects he thought could be found in a couple of acres of tropical forest.
Up to then, Erwin had mostly been a beetle counter. He’d been spraying
the tops of trees with insecticide, then collecting the carcasses that
showered down from the leaves in a brittle rain. Intrigued by the larger
question of how many insect species there were in the tropics as a whole,
he thought about how he might extrapolate from his own experience.
From a single species of tree, Luehea seemannii, he had collected beetles
belonging to more than 950 species. Figuring that about a fifth of these
beetles depended on Luehea seemannii, that other beetles similarly
depended on other trees, that beetles represent about forty percent of all
insect species, and that there are roughly fifty thousand species of
tropical trees, Erwin estimated that the tropics were home to as many as
thirty million species of arthropods. (In addition to insects, the group
includes spiders and centipedes.) He was, he acknowledged, “shocked” by
his own conclusion.
Since then, many efforts have been made to refine Erwin’s estimates.
Most have tended to revise the numbers downward. (Among other things,
Erwin probably overstated the proportion of insects dependent on a
single host plant.) Still, by all accounts, the figure remains shockingly
high: recent estimates suggest there are at least two million tropical
insect species and perhaps as many as seven million. By comparison,
there are only about ten thousand species of birds in the entire world and
only fifty-five hundred species of mammals. Thus for every species with
hair and mammary glands, there are, in the tropics alone, at least three
hundred with antennae and compound eyes.
The richness of its insect fauna means that any threat to the tropics
translates into very high numbers of potential victims. Consider the