Beetle, term referring to the insect order Coleoptera [Greek, "sheath wing"], the largest order of living organisms. Beetles occur in a wide variety of terrestrial and aquatic habitats and use many different types of food. Of the 3 to 10 million insect species worldwide, about 30-40% are beetles. In Canada 6750 species are known; an estimated 2400 have not yet been recorded. There are 143 families of beetles, 112 of which occur in Canada. These families are placed in 4 modern suborders: Archostemata, Myxophaga, Adephaga and Polyphaga.

Familiar beetles include scarabs (sacred symbol of early Egypt), weevils, and tiger, ground, blister, June and leaf beetles. Beetles are well represented as fossils, the earliest known being Upper Permian forms (256-250 million years old). Representatives of all 4 modern suborders occur in Lower Triassic deposits (250-244 million years old). With so diverse a group a specific description is difficult, but most beetles share the following characteristics.

Reproduction and Development

They pass through complete metamorphosis (eg, have distinct egg, larval, pupal and adult stages).

Structure

Larvae and adults generally have chewing mouth parts. Adults have 2 pairs of wings; the outer, horny or leathery pair (elytra) cover the inner, membranous flight wings to form a straight line down the back when at rest. In some species the inner membranous wings are reduced in size or are absent. The adult body is usually hardened; antennae vary from very short to very long and usually have 11 or fewer segments. The first segment of the thorax is free; the dorsal surface, large and shieldlike. Size ranges from 0.25 mm to over 10 cm.

Most Canadian beetles are brown or black, although an extremely wide range of colours and patterns occurs. Colour may be produced by structural modifications to the cuticle (waxy covering), producing metallic greens and blues, etc; or by pigments in the cuticle, producing oranges, reds, yellows, etc.

Range

The number of beetle species becomes markedly reduced approaching higher latitudes: only 300-400 species extend into the Canadian Arctic. Coleoptera probably is not the largest insect order in Canada; however, beetles occupy extremely varied habitats and occur throughout Canada except in the northernmost Arctic islands.

Diet

Since mobility is often somewhat restricted, the habitat of a given species is directly related to its food. Species in many families are primarily phytophagous, feeding on plant material; many are predacious, feeding on other invertebrates; some are parasites and a small number are parasitic on vertebrates. Many species are carrion, dung or pollen feeders. Larvae and adults of a species may feed on the same host; or adults may have strikingly different feeding habits from larvae, not feeding at all or using a different food source.

Interaction with Humans

Beetles are of immense economic importance, since they include many of the most destructive insect pests known. Many species attack household and stored products (eg, carpet beetles, confused flour beetle, granary weevil). Plant feeders destroy crop foliage, attacking virtually all cultivated crops. Wood borers attack nearly all trees and shrubs (eg, bark beetles, apple bark borers, poplar borers, etc).

Others transmit disease: Dutch elm disease is caused by a fungus transmitted by the elm bark beetle. Beetles do very little direct damage to humans and domestic animals. In rare cases, however, domestic animals (eg, horses) may die from eating hay containing dead blister beetles, several species of which contain toxic chemicals which cause blisters on contact with skin.

Some beetles are beneficial. Many predatory species feed on destructive insects, eg, ladybird beetles have been introduced as biological control agents of aphids and scale insects attacking crops. Families such as ground and rove beetles contain hundreds of species that feed on destructive insects and regulate their populations.

Some species considered highly beneficial in one life stage may cause damage in another life stage (eg, some larval blister beetles feed on grasshopper eggs, but adults are leaf-feeders, attacking legumes and other plants). Other beetle species are of considerable importance as pollinators, or assist in the decomposition of dead and waste organic material.