All about beetles

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Jump down to: Habitat/food sources/life cycle

Beetles are familiar to all of us, even if we don’t know to call them that — for instance, fireflies, lady bugs and June bugs are beetles. Beetles are everywhere. J.B.S. Haldane, a famous population geneticist, was once asked, regarding his studies of the world, what he had learned about the “Creator.” His reply: “An inordinate fondness for beetles.” He was referring to the fact that beetles comprise 30 percent of all insects and about 30 percent of all other animal species. Worldwide there are more than 350,000 known species in the order Coleoptera, which includes beetles and about 60,000 species of weevils. In North America, there are more than 30,000 beetle species and 1,000 weevil species.

These figures are impressive, but merely a drop in the bucket, according to scientists, who estimate there are between 5 and 8 million Coleoptera species still waiting to be discovered. In fact, new species are being discovered faster than they can be described. With so many beetles, it isn’t surprising they’re classified into a lot of different families — 134 in all.

Based on the oldest fossil found so far, beetles date back to at least 318 to 299 million years ago (the late Carboniferous Period to early Permian Period, long before the age of dinosaurs).

With the exception of oceans, beetles live nearly everywhere in the world, including Polar Regions and deserts. They have captured the imagination of people since ancient times, appearing in paintings, statuary, gemstones, jewelry and coins. Ancient Egyptians based amulets on the scarab family of beetles, who represented an earthly symbol of the sun.

Physical description
The name Coleoptera (koal-e-OP-ter-uh) comes from the Greek koleon, meaning sheath, and pteron, meaning wings — “sheath wing.” This is a reference to the hardened structure of beetles’  forewings.

Rhinoceros beetle

The imposing Eastern Hercules Beetle (Dynastes tityus) can grow to 2.4 inches (6.4 cm) long, but they’re harmless. They feed on rotting wood, rotting fruit and sap. (NPS, Evans; PD)

Beetles come in all shapes and all sizes, ranging from nearly microscopic up to 5 inches in length. Most can fly. Even so, many spend their lives on the ground or in water. Their colors are varied, ranging from drab to brightly colored or highly patterned. Some beetles are among the most beautiful insects on the planet, spectacular in iridescent palates of green-blue-violet or red, gold or copper.

Beetles have three body sections — head, thorax and abdomen. It can sometimes be hard to see all three sections, so just gently turn them on their back, which will expose the sections. Their body is usually hard, although some are soft or leathery.

Featherwing Beetle 2

Featherwing beetles are the smallest group of beetles in the U.S., some only 0.01-inch long. (Udo Schmidt / Flickr; cc by-sa 3.0)

A beetle’s head contains the eyes, and mouthparts that include hard, sometimes tooth-like, mandibles (jaws) adapted for biting and chewing. Most species also have maxillary palpus and labial palpus (PAL-pus), which are finger-like appendages which move food to the insect’s mouth. The eyes are compound, meaning they’re made up of hundreds of individual photoreceptors.* The antennae (an-TEN-ee) vary in length and type among the different species. They’re mostly used for smelling and sometimes for feeling.

Beetles have two pair of wings. The forewings are hardened and provide a protective cover for thin, delicate, somewhat-transparent hind wings. The hard forewings, called elytra (EL-uh-truh), meet in a neat line down the center of the beetle’s abdomen (back) and they’re the first clue to identifying an insect as a beetle.

The tough elytra allow some species to crawl into soil and yard debris or bore into trees without damaging their precious hind wings. What’s more, some species can trap moisture under their elytra, enabling them to live in deserts — they carry their water supply with them. Some other species trap air under their elytra and live in water.

Fiddler beetle anatomy

Fiddler Beetle anatomy. (Bugboy52.40 / Wiki; cc by-sa 3.0)

The elytra aren’t used for flight. When their wearers wish to fly they raise them up, out of the way (reminiscent of the gull-wing doors on the famous 1970s-era DeLorean cars). This clears the way for the membranous hind wings that have been folded underneath and which do the actual flying. Some beetles have lost their ability to fly and, in their case, the elytra have fused together. Many of those who do fly, seldom use their wings, spending most of their lives on the ground or in water.

A noticeable shield-like plate, called the scutellum, can be seen on the top of most beetles’ thorax.

Beetles have three pair of legs. These vary in appearance and purpose depending on how they’re used. Some have flattened, oar-like legs adapted for swimming. Others use their legs for digging or grasping. Some, like flea beetles, have legs that are enlarged and muscular for jumping.

Common Cockchafer Beetle (Melolontha melolontha) displaying elytra and hind wings at take-off. (Mario Sarto / Wiki; CC)

Habitat
Where do we find them in our yards? Some make themselves conspicuous, like the fireflies and June bugs. Others are living where they feed, so look at leaves, in or on flowers and in leaf litter. Look in rotting wood, under loose tree bark, under stones in your rock pile and, at night, under your porch lights. Elsewhere, they live in grain silos, caves and the nests of insects, such as ants. Also in the nests of birds and mammals. Some live in water or near water in sand and seashore debris. You can find a beetle nearly anywhere.

Food sources
Beetles and weevils have survived by exploiting every possible source of food — plants, trees and animals. Some beetles, as adults, don’t eat at all. Most, however, are plant eaters who, depending on the species, may eat bark, burrow through it to eat the heartwood or into soil for roots. Some eat nectar or seeds. Other species feed on rotting wood, fungi, dead organic matter, carrion or even dung. A few can become pests who defoliate trees, damage crops and weaken our garden plants.

Many beetles are predators who do us a favor by preying heavily on aphids, mealybugs, spider mites and, in some cases, other beetles that are pests. Many beetles are important recyclers of organic matter, helping to replenish nutrients in the soil. Overall, most beetles are either benign or beneficial from a human standpoint.

Life cycle
Beetles undergo complete metamorphosis. This means they pass through four stages in their development: Egg to larva to pupa to adult. The period of time from egg through adult may be as little as a few weeks or up to several years, depending on the species.

Lady beetle larva. (© James Benet / iStock)

A larva is an immature insect. A ‘baby,” so to speak, that’s still under development. Beetle larvae (LAR-vee) have well-defined heads with short antennae. They differ in appearance between species. Some don’t have legs, while others do. But one thing they all have in common is that they look very different from how they’ll  look as adults. An example is the curled, soft, whitish larvae of the stag beetle. It looks nothing like the dark, hard-bodied adult it will become. The larvae of lady beetles (ladybugs) look somewhat alligator-like. During a beetle’s larval stage, it’s an eating machine. Its sole job is to eat and grow to ready itself for pupation.

As they put on size they periodically outgrow their skin’s ability to stretch any farther, so they shed it in a process called molting. They will go through several molts on their way to the pupa stage.

For the pupal stage, larvae construct cocoons around themselves. They don’t eat and appear to be motionless. Within the cocoon, however, a great transformation is taking place. Depending on the species, they may remain in this stage from a few days to many months to years.

When the insect breaks out of its cocoon it’s a full-sized adult, ready to eat, mate and complete the last course of its life, which may range from a few weeks to a year or more.
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*A compound eye is an organ made up of hundreds, sometimes thousands, of individual photoreceptors. Each photoreceptor, called an ommatidium (oh-muh-TID-ee-um), consists of a lens and cells for distinguishing light and, sometimes, color. Compound eyes create a mosaic which an insect’s brain is able to interpret as one image. Compound eyes are particularly adept at detecting motion. This is one reason it is hard to sneak up on some insects.

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