What Is a Beetle?

What makes a beetle a beetle? Here are some distinguishing characteristics that make these “little biters” different from other insects.

| February 2015

Humans may think they rule the world, but it’s beetles that really dominate it. In The Book of Beetles, editor Patrice Bouchard goes in-depth about these creatures that make up a quarter of the world’s animals. With 400,000 known species, these insects are about as abundant as they are interesting. This excerpt, which discusses defining characteristics of beetles, is from the section “What is a Beetle?”

The English word “beetle” comes from the Middle English bityl or betyll and the Old English bitula, all of which mean “little biter.” Other commonly used names, such as “weevil” and “chafer” derived from Old English and Old High German, also relate to biting. Coleoptera, first coined by Aristotle in the fourth century bce and later adopted as an order of insects by Carl Linnaeus in 1758, is derived from the Greek words koleos, meaning “sheath,” and pteron, or “winged,” and was inspired by the tough elytra of beetles.

Distinguishing Features of Beetles

Among other adaptations, beetles are distinguished from other insects by their chewing mouthparts, the conversion of their forewings into hardened elytra, their hind wings that fold lengthwise and across beneath the elytra, and their holometabolous development. Holometabolous insects pass through four very distinct life stages: egg, larva, pupa, and adult. The larvae and adults frequently differ in habits and habitat, functioning in the environment as if they were two separate species.

Beetles, like other insects, crustaceans, arachnids, millipedes, centipedes, and their kin with segmented exoskeletons and jointed appendages (antennae, mouthparts, legs), are classified in the phylum Arthropoda. Light and durable, the beetle exoskeleton is incredibly tough and rigid or characteristically soft and pliable, and provides protection and support. It serves as a platform for important tactile and chemosensory structures externally, while providing an internal framework that supports muscles and organs. The exoskeletal surface is smooth and shiny, or dulled by waxy secretions or microscopic networks of cracks (alutaceous) resembling that of human skin. The surface is variously festooned with spines, hairlike setae, or flattened setae called scales, and sculpted with tiny bumps (tubercles), pit-like punctures, ridges, grooves (striae), or rows of punctures.

Colors of Beetles

The colors of beetles are derived either from chemical pigments obtained from their food or structural properties of the outer layers of the exoskeleton. Most beetles are black as a result of melanin deposition during sclerotization, the chemical hardening process of the exoskeleton that occurs after emergence from the pupa, or eclosion. Microscopic surface sculpturing also influences beetle colors, as do patterns of setae, scales, or waxy secretions. Black desert darkling beetles (Tenebrionidae) are sometimes partially or completely covered with a white, yellow, or bluish-gray waxy bloom that reflects light and helps to keep the beetle cool.

The brilliant iridescent and metallic colors of beetles are created by multiple reflective layers in the exoskelton and scales, or a layer of highly complex photonic crystals that reflect light at different wavelengths to create specific metallic colors and shimmering iridescence. These structures are determined genetically, but their final form in individual beetles is determined by conditions experienced during growth and development.

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