COLEOPTERAN

a member of the insect order Coleoptera, which contains the beetles and the weevils and is the largest of the insect orders. The 250,000 known coleopteran species include some of the smallest and largest of the insects: the smallest coleopterans are less than one millimetre (0.04 inch) in length, while the largest (e.g., the rhinoceros beetle Xyloryctes satyrus) can exceed 20 centimetres (8 inches). Beetles can be found in almost all environments except Antarctica and the peaks of the highest mountains. The tropics contain the most diverse beetle fauna, while in temperate zones, the fewer species are represented in greater numbers. The major diagnostic characteristic of the order is a modification of the forewings, or elytra. These may be either rigid or thickened and leathery; they lie protectively over the back and hindwings and meet in a line down the centre of the back. The hindwings are used for flying in most species. This protective modification perhaps allowed early beetles to exploit niches underneath bark, where unprotected wings would be damaged. The body is built on the general insect plan of head, thorax, and abdomen; in coleopterans, however, the last two thoracic segments are joined to the abdomen, and the prothorax stands alone under a protective plate called the pronotum. The legs may be adapted for running, digging, swimming, or jumping. The antennae are normally composed of 11 segments, but their form may vary widely. Depending on the diet, the mandibles may be quite large or nearly absent. Most coleopterans possess a pair of prominent compound eyes. With so many species in the order, it is not surprising that there is a great diversity of forms and adaptations. In many beetles the elytra are brightly coloured or patterned. The rather generalized Carabidae (ground beetles) have an oval, flattened body with medium-length appendages; in water beetles (Hydrophilidae) the underside is very smooth and there are long hairs on the hindlegs that give greater surface area when paddling; ladybugs (Coccinellidae) are very round in contour and flat below; stag beetles (Lucanidae) have enormously enlarged mandibles; the long-horned wood-boring beetles (Cerambycidae) have exceptionally long antennae and are frequently very slender of body; the fireflies (Lampyridae) have soft elytra and can produce light; and the weevils (Curculionidae) have their mouths at the tip of an extended snout. Beetles live on plants, underground, in the water, as commensals in the nests of various social insects, in rotten logs, and in myriad other habitats. Many beetles are predaceous. Adult ground beetles are nocturnal and feed on various insects and snails. Both larval and adult diving beetles (Dytiscidae) eat insects and small fish and frogs. Ladybugs eat large numbers of aphids and scale insects, while soldier beetles (Cantharidae) prefer worms and various insect larvae, and fireflies take mostly snails. Another large group of coleopterans eats plants. In this group are the June beetles (Melolonthinae), seed beetles (Bruchidae), handsome fungus beetles (Endomychidae), and leaf beetles (Chrysomelidae). False darkling beetles (Melandryidae) feed on rotting wood, while the skin beetles (Dermestidae) and spider beetles (Ptinidae) are scavengers on dead animal skins and the like. Several members of the Scarabaeidae, as well as other groups, feed on dung. Among the insects, beetles are moderately well armoured, but they are still subject to a fair amount of predation. Bats, swifts, frogs, and certain other insects, including other beetles, will attack them. Tachinid flies parasitize adult beetles and various wasps parasitize beetle larvae. Certain species are involved in complex relationships with other living things. Some beetles dwell in nests of ants or termites. Many of these forms have lost their wings, as flight is unnecessary, and some have glands that secrete substances attractive to the host species. Certain ambrosia beetles (Scolytidae) share their arboreal habitat with particular fungi. They have evolved structures on which to transport this fungus when moving to a new tree. Most beetles are bisexual and lay eggs, although there are a few parthenogenetic species in which fertilization is not necessary. Coleopterans undergo a complete metamorphosis composed of four developmental stages: egg, larva, pupa, and adult. After copulation the female beetle stores sperm in a saclike spermatheca until the eggs are ready for fertilization. Once fertilized the eggs may be laid singly or in small clutches. They are usually placed near a source of food for the larvae; wood-boring species lay their eggs in tree trunks, while foliage eaters leave them on a leaf. Larvae may be long and tapered (Staphylinidae and Silphidae, the rove and carrion beetles), cylindrical and hard-surfaced (Elateridae, the click beetles), tapered with a bristly covering (dermestids), or soft-bodied and C-shaped (scarabaeids). The larvae may be predatory or phytophagous and do not necessarily feed on the same diet as the adults. Larvae go through three to five molts before they pupate. The pupa resembles the adult except that it is soft and its wings are encased. When the thin pupal skin is shed the adult emerges. Because of their abundance many species of Coleoptera are considered pests in their impact on man. The leaf beetles and weevils have serious adverse effects on many crops. Carpet beetles (Dermestidae) can ruin various fabrics and clothing. Lumber is frequently damaged by powder-post beetles (Lyctidae) and deathwatch beetles (Anobiidae). Certain beetles also transmit diseases from plant to plant; Dutch elm disease, for instance, is carried by the bark beetle Scolytus multistriatus. any member of the insect order Coleoptera, which includes the beetles and weevils. It is the largest order of insects, representing about 40 percent of the known insect species. Among the approximately 250,000 species of Coleoptera are many of the largest and most conspicuous insects, some of which also have brilliant metallic colours, showy patterns, or striking form. Beetles can usually be recognized by their two pairs of wings; the front pair is modified into horny covers (elytra) that hide the rear pair and most of the abdomen and usually meet down the back in a straight line. Coleoptera occur in nearly all climates. They may be divided into four groups: the first three, the Archostemata, the Adephaga, and the Myxophaga, contain relatively few families; the majority of beetles are placed in the fourth group, the Polyphaga. Beetles attract attention for many different reasonseconomic importance, size, abundance, appearance, and remarkable habits. Several groups of beetles (e.g., Lampyridae) are among the few terrestrial animals capable of producing light; members of several other families (e.g., Cerambycidae) can produce sound (stridulate). Most large beetles make a loud noise during flight, and many species, both large and small, are attracted to light at night. Some beetles (e.g., burying beetles of the family Silphidae and whirligig beetles of the family Gyrinidae) attract attention by their bizarre habits; others do so by their grotesque forms (e.g., Scarabaeidae). Many beetles have become adapted to an aquatic environment (e.g., Hydrophilidae); others (e.g., Thorictidae) live in association with ants and termites. Additional reading General In addition to information given in textbooks of entomology, the following works should be consulted: J.R. Dibb, Field Book of Beetles (1948); G. Taylor, Some British Beetles (1948); United States Department of Agriculture, Insects, 1952 Yearbook of Agriculture (1952), many chapters of this work are devoted to pestiferous beetlestheir ravages and control; A.G. Bving and F.C. Craighead, An Illustrated Synopsis of the Principal Larval Forms of the Order Coleoptera, Ent. Amer., vol. 11 (193031); J.H. Fabre, Souvenirs entomologiques, 10 vol. (18791907). Many of these detailed popular accounts of natural history are available in English. A standard anatomical and biological work, based upon a study of the water beetle Dytiscus, is E. Korschelt, Der Gelbrand Dytiscus marginalis, 2 vol. (192324). See also Ross H. Arnett, N.M. Downie and H.E. Jacques, How to Know the Beetles, 2nd ed. (1980); Richard E. White, A Field Guide to the Beetles of North America (1983). Advanced R.A. Crowson, The Natural Classification of the Families of Coleoptera (1955, reprinted 1967), a descriptive synopsis of all families of beetles, with illustrated key, and many new arrangements; W.W. Fowler, Coleoptera: General Introduction and Cicindelidae and Paussidae (1912), a general treatment of morphology, including the internal anatomy of beetles, with a general discussion of organs, biology, and classification; J.T. Lacordaire, Histoire naturelle des insectes: genera des coloptres, ou expos mthodique et critique de tous les genres proposs jusqui'ici dans cet ordre d'insectes, 12 vol. (185476, reprinted 195472), the standard work on all the families and genera of beetles known at the time, still extremely useful, with keys to all categories (in French).Catalogs of the species of Coleoptera include the Catalogus Coleopterorum Europae, 2nd ed. (1906) by L. Heyden, E. Reitter, and J. Weise; C.W. Leng, Catalogue of the Coleoptera of America, North of Mexico (1920), with five supplements (192748); W. Junk, Coleopterorum Catalogus, 31 vol. (191040); R.E. Blackwelder (comp.), Checklist of the Coleopterous Insects of Mexico, Central America, the West Indies, and South America, 6 pt. (194457, reprinted 1982). Judson Linsley Gressitt Classification Distinguishing taxonomic features One distinctive feature of coleopterans is wing structure. Most beetles have two pairs of wings. The front pair, which may be thickened, leathery, or hard and brittle, are called elytra and usually serve only as protective covers. A few beetles have greatly reduced wings. Variations in the structure of the first abdominal segment is one criterion used to separate the various suborders of Coleoptera; the hind coxal leg segments (by which the legs are attached to the body) may divide the abdominal segment partially or completely. Sometimes the abdominal segments are fused, the articulations marked by form sutures. Variation in length, texture, and appearance of elytra, as well as the number of abdominal segments exposed by short elytra, are used to distinguish the various superfamilies. Characters associated with the size and shape of the coxae also are used as distinguishing features. Structure of antennae and legs are important considerations for taxonomic criteria, as are larval structure, head structure (including mandibles, or jaws), pattern of veins in wings, habitats, and behaviour. Annotated classification About 135 families of beetles are known, of which 120 occur in the Western Hemisphere. There have been a number of different classifications of Coleoptera. Many were based on the suborders Adephaga and Polyphaga; the latter, which contains about 90 percent of the beetles, included a number of divisions (e.g., clavicorns, serricorns, lamellicorns, phytophagous beetles, and weevils). Sometimes these divisions are considered as superfamilies or series, and sometimes (particularly weevils and relatives) as suborders. The classification below is based on that of R.A. Crowson (1955); it includes four suborders.