How Many Beetle Species Are There? Why Beetles Rule Earth

How many beetle species are there?

Beetles form the insect order Coleoptera, a name that means “sheath wings” and refers to their hardened front wings. Around 400,000 species have been formally named and described. That is about 40 percent of all described insects and about 25 percent of all known animal species, from sponges to whales.

The real number is certainly higher, because many beetles live in tropical forest canopies, soil and leaf litter where few scientists have looked. A 2015 study by Nigel Stork and colleagues combined several estimation methods and arrived at about 1.5 million beetle species, with a likely range of roughly 0.9 to 2.1 million. Older estimates, based on fogging tropical treetops with insecticide and counting the beetles that fell, were sometimes far higher, but these are now thought to be exaggerated.

Some insect experts think flies or wasps may rival beetles once all their species are found, because so many tiny parasitic wasps and flies remain unnamed. For now, beetles hold the record.

The biggest beetle families

Beetles are divided into roughly 180 or more families, depending on the classification used. A handful of them contain an enormous share of all species:

• Weevils (Curculionidae and relatives): plant-eating beetles with a long snout, like the acorn weevil in the photo. Tens of thousands of species, often named as the largest family of all animals.
• Rove beetles (Staphylinidae): slim beetles with very short wing cases, found in leaf litter, dung and fungi. Also tens of thousands of species.
• Ground beetles (Carabidae): fast-running, mostly predatory beetles, with around 40,000 species.
• Leaf beetles (Chrysomelidae) and longhorn beetles (Cerambycidae): each with tens of thousands of species of plant eaters.
• Scarab beetles (Scarabaeidae): including dung beetles, chafers and giants such as the Hercules beetle.

Familiar groups are only small slices of this diversity. Ladybugs number about 6,000 species, and stag beetles, such as the European stag beetle, form a family of only a little over a thousand species.

Why are there so many beetles?

No single reason explains the success of beetles, but scientists point to several factors working together.

Armor that opens up new habitats. A beetle’s hard front wings, called elytra, fold over the delicate flying wings and the body like a protective case. This lets beetles burrow into soil, wood, dung, carcasses and leaf litter without damaging their wings, and still fly away to find new places to live.

Two lives in one. Beetles go through complete metamorphosis: egg, larva, pupa and adult. Larvae and adults often eat completely different food and live in different places, so a single species can exploit two niches without competing with itself.

A huge range of diets. Beetles eat leaves, roots, seeds, wood, fungi, pollen, dung, dead animals and other insects. Many plant-eating beetles specialize on one group of plants, and the spread of flowering plants over the last 100 million years or so is thought to have helped them diversify, although the details are debated.

A long history with few extinctions. Beetles appeared about 295 million years ago in the Permian period. Studies of the fossil record suggest that beetle families have rarely gone extinct, even through mass extinctions, so new species have kept accumulating for a very long time.

Small size. Most beetles are only a few millimeters long. Small animals can divide a habitat into many tiny niches, a single tree can host hundreds of beetle species, and isolated populations easily split into new species.

Haldane’s “inordinate fondness for beetles”

The most famous comment on beetle diversity is attributed to the British biologist J. B. S. Haldane. Asked what his studies of nature revealed about the Creator, he is said to have replied that God has “an inordinate fondness for beetles”. The quip became widely known after the American ecologist G. Evelyn Hutchinson retold it in his 1959 essay on why there are so many kinds of animals.

The exact wording is uncertain. No recording or text in Haldane’s own hand gives the line, and versions differ, using phrases such as “an inordinate fondness for beetles” or “for stars and beetles”. It is best treated as a well-loved anecdote rather than an exact quotation.

Beetles from the smallest to the largest

The range of sizes within this one order is astonishing. The smallest known beetles, featherwing beetles, can be about a third of a millimeter long, smaller than some single-celled organisms. At the other extreme, the titan beetle and the Hercules beetle reach about 17 cm (7 in), more than 500 times longer, as explained in what is the biggest beetle in the world.

Beetles live on every continent except Antarctica and in almost every habitat on land and in fresh water, from deserts and mountain tops to caves and ponds. Only the open sea has almost no beetles.

How many beetles live near you?

Beetle diversity is greatest in the tropics, but temperate regions have plenty too. Around 4,000 beetle species are known from Britain, and roughly 25,000 from North America north of Mexico. A single garden can hold hundreds of species, from ladybugs such as the seven-spot ladybug to ground beetles, weevils, click beetles and rove beetles hidden under stones and in compost.

New species are still being described every year, even in Europe and North America, and more than a thousand new beetle species are named worldwide in a typical year. For anyone curious about nature, beetles remain one of the best groups in which to make a real discovery.