BILLIONS OF BEETLES

There is a bit of old gossip that continues to be retold amongst biologists. According to this tale, the eminent British biologist, J. B. S. Haldane, was attending a cocktail party when he was confronted by a prelate with a rather unusual question. Repeated ever since the late 1930s, this brief encounter has become a staple when discussing the diversity of life on our planet. The religious gentleman's question was: "As a student of biology, Dr. Haldane, what can you tell us about the nature of God?" Unfazed by the gravity of the question, the eminent biologist is said to have responded simply and directly: "An inordinate fondness for beetles!"

Yes indeed! The Creator seems to have a fondness for beetles. Why else would there be so many of them? At latest count, beetles number around 380,000 described species. What this means is that a student of insects has gone to the trouble of providing the description for a new species, given it a Latin name, designated the specimens to which the name applies, and published all this in a scientific text or periodical. Nowadays, students of insects (entomologists) like to have an illustration published along with the description of a new species, and they insist that a designated specimen — the type specimen — be deposited in a public museum or a university collection. All this effort, all over the world, has given us around 380,000 scientific names for beetles! Compare that with about 5,500 species of described living mammals, or a bit more than 10,000 species of birds. Shifting to the plant world, there are over 310,000 described species of land plants on our resplendent planet. This is a conservative number, including mosses, liverworts, ferns and their allies, all the conifers, as well as more than a quarter million flowering plants. Add all these green plants together and they still don't reach a number of species that can match the beetles. Returning to animals, there seem to be more species of beetles than there are species of all the non-microscopic animals living in all the oceans. This aquatic crowd includes jellyfish, many kinds of worms, mollusks of all sorts, lots of crabs, and thousands of fish species. Three-hundred and eighty thousand described species are a whole lot of species! And, as if that weren't trouble enough, their numbers keep growing as scientists discover new and undescribed species living high in rainforest trees, and even little ones hiding in the soil not far from where many of us live.

WHY ARE THERE SO MANY KINDS OF BEETLES?

Beyond God's pleasure, what might be the reasons for beetles being so numerous? Like so many puzzles in biology, this question elicits many answers. Surely, the first of many factors is the most obvious: beetles are little. The largest weigh about as much as a mouse, the smallest less than a fly. In strong contrast: there are fewer than a dozen species of rhinos and elephants alive in the world today. These are the largest and heaviest land animals, each requiring a range of many square kilometers in which to live and prosper. Beetles, on the other hand, can live their short lives within only a few square meters. Here we have a pattern seen throughout the living world: numbers of both individuals and species decline as the sizes of animals increase. Clearly, being small makes it possible to pack a lot of beetles into the same small area.

Small size is just one factor helping us understand the diversity of beetles. Beetles are found in many diverse habitats, carrying on a grand variety of life activities. Huge numbers live in both temperate and tropical regions; a few can be found in the tundra and on high mountains, but none are resident in Antarctica. We know how flour beetles can invade our kitchens, carpet beetles damage wool rugs, and Japanese beetles chew on garden plants. In a warm June evening, june bugs (really beetles) fly into our screens, while fireflies (also beetles) flash signals in the dark of early evening. In addition to a grand number of species, some beetle species have populations made up of millions of individuals.

In the American West, ladybird beetles (also called ladybugs) move high into the mountainsides and congregate together to spend the winter. During the early 1900s, collectors would go into the Sierra Madre highlands of California to collect these slumbering beetles, selling them to farmers in their battle against aphids. (Ladybird beetles, both larvae and adults, feed on aphids.) This collecting activity, in the early part of the last century, saw the gathering of several tons — that's right tons — of beetles each winter. When you calculate that there may be 44,344,000 ladybird beetles in a ton of 'em, you've got a real lot of beetles. The take-home message is clear: by combining 380,000 species of beetles, with populations that may reach millions of individuals, it is no exaggeration to claim that our planet does indeed support billions of beetles. But what is it about beetles that have made them such a grand success?

Extinction is a constant erosive force in the history of life. A long fossil record tells us that perhaps 98 percent of all the species that ever lived are already long gone. Surviving changing climates, droughts, disease pandemics, and the occasional geological upheaval is a challenge a great majority of plants and animals have failed. Thus, when we see a lineage as successful as the beetles, we know they've got to be a well-adapted crowd. In fact, a simple glance at most any beetle will reveal their primary survival attribute: they are tough. Trekking over the leafy forest floor you can step on nearly any beetle, only to have it scurry away as you lift your boot. A hard exoskeleton amply protects a delicate interior! The key innovation here is that what was once a forward pair of wings became modified into hard wing covers (elytra) protecting the top of the entire abdomen. Their front and bottom sides are also armor encased. In fact, many species look like miniature tanks. The "Volkswagen beetle" got its moniker because this automobile really did resemble some beetles. Best of all, the tough wing covers of beetles can be raised up, allowing the actual wings to unfold and fly into the distance. Being rather solid means that, while most beetles can fly, they are neither fast nor agile. And that's why the larger ones fly only at night, avoiding the pursuit of predatory birds in the light of day. Being well protected, and with the ability to fly, gives them two significant...