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(Explore the five vital roles insects play in our ecosystem.)
People may delight in butterflies and detest mosquitoes, but most insects we simply ignore. This says way more about creatures with two legs than it does about creatures with six.
Insects are far and away the most diverse creatures on the planet, so much so that scientists are still struggling to figure out how many different kinds there are. About a million insect species have been named, but it’s generally agreed that many more—by recent estimates some four million more—have yet to be discovered. Just one family of parasitoid wasps, the Ichneumonidae, sometimes called Darwin wasps, contains something like 100,000 species, greater than the number of all known species of fish, reptiles, mammals, amphibians, and birds combined. (The mere existence of the Ichneumonidae, Charles Darwin once argued to a friend, was enough to disprove the biblical theory of creation, as no “beneficent and omnipotent God” would have designed such a ghoulish, murderous parasite.) Other insect families are similarly big; there are, for example, perhaps 60,000 species of Curculionidae, commonly known as weevils.
In keeping with their extraordinary variety, insects are found in virtually every type of terrestrial habitat, including the most extreme. Stone flies have been recorded in the Himalaya at elevations above 18,000 feet, and silverfish in caves 3,000 feet below Earth’s surface. The Yellowstone hot springs alkali fly lives at the edges of scalding pools, while the wingless midge Belgica antarctica survives the cold by coating its eggs in a kind of antifreeze gel. A fly known as the sleeping chironomid, native to semiarid regions in Africa, has larvae that shrink to desiccated flakes in very dry times, entering a kind of suspended animation from which they have been observed to recover after more than 15 years.
What accounts for the tremendous variety of insects? Many explanations have been offered, the simplest being that insects are old. Very old. They were among the earliest animals to colonize land, more than 400 million years ago—nearly 200 million years before the first dinosaurs appeared. Such an extended history has allowed insect diversity to build up over time.
But having the ability to occupy many different environmental niches probably also mattered. Insects are so small that a single tree can be home to hundreds of kinds, some boring into the bark, others tunneling into the leaves, still others feeding on the roots. This sort of “resource partitioning,” as ecologists call it, allows many species of insects to inhabit more or less the same space.
Then there’s the fact that insects, historically at least, have had low extinction rates. A few years ago researchers examined the fossil record of the largest suborder of beetles, Polyphaga, a group that includes scarabs, click beetles, and fireflies. They found that not a single family in the group had gone extinct in its entire evolutionary history, even during the mass extinction at the end of the Cretaceous period, 66 million years ago. The finding makes recent declines seem all the more ominous.
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