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Colorado potato beetle.jpg
Type: Insects
Order: Coleoptera
Metamorphosis: Complete

Beetles are the most diverse group of insects. Their order, Coleoptera (meaning "sheathed wing"), has more described species in it than in any other order in the animal kingdom. Forty percent of all described insect species are beetles (about 350,000 species), and new species are regularly discovered. Estimates put the total number of species, described and undescribed, at between 5 and 8 million. For this reason, the Scottish geneticist J. B. S. Haldane, when asked what his studies of nature revealed about God, replied, "An inordinate fondness for beetles."

Beetles can be found in almost all habitats, but are not known to occur in the sea or in the polar regions. They impact the ecosystem in several ways. On the one hand, they feed on plants and fungi, break down animal and plant debris, and eat other invertebrates. On the other hand, they are prey of various animals including birds and mammals. Certain species are agricultural pests, such as the red flour beetle Tribolium castaneum, the Colorado potato beetle Leptinotarsa decemlineata, or the mungbean beetle Callosobruchus maculatus, while others are important controls of agricultural pests. For example, Lady Beetles (family Coccinellidae) consume Aphids, Scale Insects, Thrips, and other plant-sucking insects that damage crops.


The general anatomy of beetles is quite uniform, though specific organs and appendages may vary greatly in appearance and function between the many families in the order. Beetle bodies are divided into three sections: the head, the thorax, and the abdomen. When viewed from below, the thorax is that part from which all three pairs of legs arise. The abdomen, then, is everything posterior to the thorax. When viewed from above, most beetles appear to have three clear sections, but this is deceptive: on the beetle's upper surface, the middle "section" is a hard plate called the pronotum, which is only the front part of the thorax; the back part of the thorax is concealed by the beetle's wings. Like all insects, beetles are [segmented organisms, and all three of the major sections of the body are themselves composed of several further segments, although these are not always readily discernible. This further segmentation can usually best be seen on the abdomen.


In some beetles the ability to fly has been lost, most notably in the Ground Beetles (family Carabidae) and the "true Horticulture/Weevils" (family Curculionidae), but also in some desert and cave-dwelling species of other families. Many of these species have the two elytra fused together, forming a solid shield over the abdomen. In a few families, both the ability to fly and the elytra have been lost, with the best known example being the glowworms of the family Phengodidae, in which the females are larviform throughout their lives.




The legs, which are multi-segmented, end in two to five small segments called tarsi, which are vaguely comparable to feet. Like many other insect orders beetles bear claws, usually one pair, on the end of the last tarsal segment of each leg. While most beetles use their legs for walking, legs may be variously modified and adapted for other uses. Among aquatic families — predacious diving beetles (Dytiscidae), crawling water beetles (Haliplidae), many water scavenger beetles (Hydrophilidae), and others — the legs, most notably the hind pair, are modified for swimming and often bear rows of long hairs to aid this purpose. Other beetles have fossorial legs that are widened and often spined for digging. Species with such adaptations are found among the scarabs, ground beetles, and clown beetles (family Histeridae). The hind legs of some beetles, such as Flea Beetles (within Chrysomelidae) and flea weevils (within Curculionidae), are enlarged and designed for jumping.



Life Cycle[edit]

Scarabaeiform larva of the cockchafer, Melolontha melolontha

Beetles undergo complete metamorphosis, meaning that the larval form does not resemble the adult.


The larva is usually the principal feeding stage of the beetle lifecycle. Larvae tend to feed voraciously once they emerge from their eggs. Some feed externally on plants, such as those of certain leaf beetles, while others feed within their food sources. Examples of internal feeders are most metallic wood-boring beetles (family Buprestidae) and longhorn beetles. The larvae of many beetle families are predatory like the adults (ground beetles, lady beetles, rove beetles). The larval period varies between species but can be as long as several years.







Pairing is generally short but in some cases will last for several hours. During pairing sperm cells are transferred to the female to fertilize the eggs.

Striped love beetle Eudicella gralli from the forests of Central Africa. The iridescent elytra are used in marriage ceremonies.

Parental care varies between species, ranging from the simple laying of eggs under a leaf to certain scarab beetles, which construct impressive underground structures complete with a supply of dung to house and feed their young. Other beetles are leaf rollers, biting sections of leaves to cause them to curl inwards, then laying their eggs, thus protected, inside.



Camouflage involves the use of colouration or shape to blend into the surrounding environment. Among those that exhibit this defensive strategy are some of the leaf beetles (family Chysomelidae), having green colouring very similar to their habitat on plant leaves. More complex camouflage also occurs, as with some weevils, where various coloured scales or hairs cause the beetle to resemble bird dung.

Another defence that often uses colour or shape to deceive potential enemies is mimicry. A number of longhorn beetles (family Cerambycidae) bear a striking resemblance to wasps, which fools predators into keeping their distance even though the beetles are in fact harmless. This defence can be found to a lesser extent in other beetle families, such as the scarab beetles. Beetles may combine their colour mimicry with behavioural mimicry, acting like the wasps they already closely resemble.

Many beetle species, including Lady Beetles and Blister Beetles, can secrete distasteful or toxic substances to make them unpalatable or even poisonous. These same species often exhibit aposematism, where bright or contrasting colour patterns warn away potential predators.

Large ground beetles and longhorn beetles may go on the attack, using their strong mandibles to forcibly persuade a predator to seek out easier prey. Others, such as bombardier beetles (within Carabidae) spray acidic gas from their abdomen to repel predators.

Symptoms and Signs[edit]

Host plants[edit]






Adaptations to the environment[edit]

Aquatic beetles use several techniques for retaining air beneath the water's surface. Predaceous diving beetles hold air between the abdomen and the elytra when diving. Water scavenger beetles have hairs on their under surface that retain a layer of air against their bodies. Adult crawling water beetles use both their elytra and their hind coxae (the basal segment of the back legs) in air retention (Roughley 2001) while whirligig beetles simply carry a bubble down with them whenever they dive.

Impact on humans[edit]


Damage to beans by larvae of the common bean weevil, Acanthoscelides obtectus

Many agricultural, forestry, and household insect pests are members of this order. Some of these are:


Beneficial organisms[edit]

  • Both the larvae and adults of some lady beetles (family Coccinellidae) are found in aphid colonies. Other lady beetles feed on scale insects and mealybugs. If normal food sources are scarce they may feed on other things, such as small caterpillars, young plant bugs, aphid honeydew, and plant nectar.
  • Ground beetles (family Carabidae) are common predators of many different insects and other arthropods, including fly eggs, caterpillars, wireworms, many and others.

Some farmers develop w:beetle banks to foster and provide cover for beneficial beetles.

Ancient Egyptian scene depicting a scarab beetle



  • Roughley, R.E. 2001. Haliplidae. pp. 138-143 in R.H. Arnett Jr. and M.C. Thomas (Eds.), American Beetles, Volume 1. CRC Press, Boca Raton, FL.