The Carabidae, or ground-beetles, comprising 13,000 species, form FIG.
The identification of the elytra of beetles with the fore-wings of other insects has indeed been questioned (1880) by F.
As regards growth after hatching, all beetles undergo a "complete" metamorphosis, the wing-rudiments developing beneath the cuticle throughout the larval stages, and a resting pupal stage intervening between the last larval instal1 and the imago.
Two very small families of aquatic beetles seem to stand at the base of the series, the Amphizoidae, whose larvae are broad and well armoured with FIG.
Riding past the pond where there used always to be dozens of women chattering as they rinsed their linen or beat it with wooden beetles, Prince Andrew noticed that there was not a soul about and that the little washing wharf, torn from its place and half submerged, was floating on its side in the middle of the pond.
Firefly is a term popularly used for certain tropical American click-beetles (Pyrophorus), due to their power of emitting light.
The name "firefly" is often applied also to luminous beetles of the family Lampyridae, to which the well-known glow-worm belongs.
It is possibly for the purpose of feeding on parasitic mites that book-scorpions lodge themselves beneath the wing-cases of large tropical beetles; and the same explanation, in default of a better, may be extended to their well-known and oft-recorded habit of seizing hold of the legs of horse-flies or other two-winged insects.
Many larvae of beetles, moths, &c., bore into bark, and injure the cambium, or even the wood and pith; in addition to direct injury, the interference with the transpiration current and the access of other parasites through the wounds are also to be feared in proportion to the numbers of insects at work.
COLEOPTERA, a term used in zoological classification for the true beetles which form one of the best-marked and most natural of the orders into which the class Hexapoda (or Insecta) has been divided.
In many beetles the hindwings are reduced to mere vestiges useless for flight, or are altogether absent, and in such cases the two elytra are often fused together at the suture; thus organs originally intended for flight have been transformed into an armour-like covering for the beetle's hind-body.
Tower (1903), of nervures similar to those of the hind-wing, and by the proof that the small membranous structures present beneath the elytra of certain beetles, believed by Meinert to represent the whole of the true fore-wings, are in reality only the alulae.
The tergite of the prothorax (pronotum) is prominent in all beetles, reaching back to the bases of the elytra and forming a substantial shield for the front part of the body.
2, a), while in many beetles that burrow into the earth or climb about on trees the fore-legs are broadened and strengthened for digging, or lengthened and modified for clinging to branches.
In male beetles, however, the two pairs of genital processes (paramera) belonging to the ninth abdominal segment are always present, though sometimes reduced.
In the structure of the digestive system, beetles resemble most other mandibulate insects, the food-canal consisting of gullet, crop, gizzard, mid-gut or stomach, intestine and rectum.
The nervous system is remarkably concentrated in some beetles, the abdominal ganglia showing a tendency to become shifted forward and crowded together, and in certain chafers all the thoracic and abdominal ganglia are fused into a single nervecentre situated in the thorax, - a degree of specialization only matched in the insectan class among the Hemiptera and some muscid flies.
The most striking feature in the development of beetles is the great diversity noticeable in the outward form of the larva in different families.
Extremes we find various transitional forms: an active larva, as described above, but with four-segmented, single-clawed legs, as among the rove-beetles and their allies; the body well armoured, but slender and worm-like, with very short legs as in wireworms and mealworms (figs.
In the case of certain beetles whose larvae do not find themselves amid appropriate food from the moment of hatching, but have to migrate in search of it, an early larval stage, with legs, is followed by later sluggish stages in which legs have disappeared, furnishing examples of what is called hypermetamorphosis.
Most of the dominant families - such as the Carabidae (ground-beetles), Scarabaeidae (chafers), or Curculionidae (weevils) have a distribution as wide as the order.
But while some large families, such as the Staphylinidae (rove-beetles) are especially abundant on the great northern continents, becoming scarcer in the tropics, others, the Cicindelidae (tiger-beetles), for example, are most strongly represented in the warmer regions of the earth, and become scarce as the collector journeys far to south or north.
The distribution of many groups of beetles is restricted in correspondence with their habits; the Cerambycidae (longhorns), whose larvae are wood-borers, are absent from timberless regions, and most abundant in the great tropical forests.
The Amphizoidae, for example, a small family of aquatic beetles, are known only from western North America and Eastern Tibet, while an allied family, the Pelobiidae, inhabit the British Isles, the Mediterranean region, Tibet and Australia.
The beetles of the British islands afford some very interesting examples of restricted distribution among species.
In general it may be stated that beetles live and feed in almost all the diverse ways possible for insects.
Some of the scavengers, like the burying beetles, inter the bodies of small vertebrates to supply food for themselves and their larvae, or, like the "sacred" beetle of Egypt, collect for the same purpose stores of dung.
Many beetles of different families have become the "unbidden guests" of civilized man, and may be found in dwelling-houses, stores and ships' cargoes, eating food-stuffs, paper, furniture, tobacco and drugs.
Hence we find that beetles of some kind can hold their own anywhere on the earth's surface.
A large number of beetles inhabit the deep limestone caves of Europe and North America, while many genera and some whole families are at home nowhere but in ants' nests.
Most remarkable is the presence of a number of beetles along the seashore between tide-marks, where, sheltered in some secure nook, they undergo immersion twice daily, and have their active life confined to the few hours of the low ebb.
In correlation with their heavy build and the frequent loss of the power of flight, many beetles are terrestrial rather than aerial in habit, though a large proportion of the order can fly well.
The chin (gula) is a very characteristic stlerite in beetles, absent only in a few families, such as the weevils.
- Water Beetles (Dyticidae).
Many beetles make a hissing or chirping sound by rubbing a "scraper," formed by a sharp edge or prominence on some part of their exoskeleton, over a "file" formed by a number of fine ridges situate on an adjacent region.
The file may be on the head - either upper or lower surface - and the scraper formed by the front edge of the prothorax, as in various wood-boring beetles (Anobium and Scolytus).
In a large number of beetles of different families, stridulating areas occur on various segments of the abdomen, and are scraped by the elytra.
Stridulating organs among beetle-larvae have been noted, especially in the wood-feeding grub of the stag-beetles (Lucanidae) and their allies the Passalidae, and in the dung-eating grubs of the dor-beetles (Geotrupes), which belong to the chafer family (Scarabaeidae).
Whatever may be the true explanation of stridulating organs in adult beetles, sexual selection can have had nothing to do with the presence of these highly-developed larval structures.
Some beetles emit a bright light from a portion of their bodies, which leads to the recognition of mate or comrade by sight.
The well-known "fire-flies" of the tropics are large click-beetles (Elateridae), that emit light from paired spots on the prothorax and from the base of the ventral abdominal region.