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HETEROMERA

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Originally appearing in Volume V06, Page 675 of the 1911 Encyclopedia Britannica.
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HETEROMERA.—ThiS tribe is distinguished by the presence of the normal five segments in the feet of the fore and intermediate legs, while only four segments are visible in the hind-foot. Considerable diversity is to be noticed in details of structure within this group, and for an enumeration of all the various families which have been proposed and their distinguishing characters the reader is referred to one of the monographs mentioned below. Some of the best-known members of the group belong to the Tenebrionidae, a large FIG. 21.-(a) Tenebrio molitor FIG. 22.—Blaps mortisaga (Flour Beetle). Europe. (b) (Churchyard Beetle). Europe. Larva, or mealworm. family containing over Io,000 species and distributed all over the world. The tenebrionid larva is elongate, with well-chitinized cuticle, short legs and two stumpy tail processes, the common meal-worm (fig. 21) being a familiar example. Several species of this family are found habitually in stores of flour or grain. The beetles have feelers with eleven segments, whereof the terminal few are thickened so as to form a club. The true " black-beetles " or " churchyard beetles " (Blaps) (fig. 22) belong to this family; like members of several allied genera they are sooty in colour, and some-what resemble ground beetles (Carabi) in general appearance. The most interesting of the Heteromera, and perhaps of all the Coleoptera, are some beetles which pass through two or more larval forms in the course of the life-history (hypermetamorphosis). These belong to the families Rhipidophoridae and Meloidae. The latter are the oil beetles (fig. 23) or blister beetles (fig. 24), insects with rather soft cuticle, the elytra (often abbreviated) not fitting closely to the sides of the abdomen, the head constricted behind the eyes to form (Oil Beetle). Europe. (Blister Beetle). Europe. ' a neck, and the claws of the feet divided to the base. Several of the Meloidae (such as the " Spanish fly," fig. 24) are of economic importance, as they contain a vesicant substance used for raising medicinal blisters on the human skin. The wonderful transformations of these insects were first investigated by G. Newport in 1851, and have recently been more fully studied by C. V. Riley (1878) and J. H. Fabre. The first larval stage is the " triungulin," a tiny, active, armoured larva with long legs (each foot with three claws) and cercopods. In the European species of Sitaris and Meloe these little larvae have the instinct of clinging to any hairy object. All that do not happen to attach themselves to a bee of the genus Anthophora perish, but those that succeed in reaching the right host are carried to the nest, and as the bee lays an egg in the cell the triungulin slips off her body on to the egg, which floats on the surface of the honey. After eating the contents of the egg, the larva moults and becomes a fleshy grub with short legs and with paired spiracles close to the dorsal region, so that, as it floats in and devours the a honey, it obtains a supply of air. After a resting (pseudo-pupal) stage and another larval stage, the pupa is developed. In the American Epicauta vittata the larva is parasitic on the eggs and egg-cases of a locust. The triungulin searches for the eggs, and, after a moult, becomes changed into a soft-skinned tapering larva. This is followed by a resting (pseudo-pupal) stage, and this by two successive larval stages like the grub of a chafer. The Rhipidophoridae are beetles with, short elytra, the feelers pectinate in the malesand serrate in the females. The life-history of Metoecus has been studied by T. A. Chapman, who finds that the eggs are laid in old wood, and that the triungulin seeks to attach itself to a social wasp, who carries it to her nest. There it feeds first as an internal parasite of the wasp-grub, then bores its way out, moults and devours the wasp larva from outside. The wasps are said to leave the larval or pupal Metoecus unmolested, but they are hostile to the developed beetles, which hasten to leave the nest as soon as possible. ST REPSIPTERA.-MUCh difference of opinion has prevailed with regard to the curious, tiny, parasitic insects included in this division, some authorities considering that they should be referred to a distinct order, while others would group them in the family Meloidae just described. While from the nature of their life-history there is no doubt that they have a rather close relationship to the Weloidae, their structure is so remarkable that it seems advisable fo regard them as at least a distinct tribe of Coleoptera. They may be comprised in a single family, the Stylopidae. The males are very small, free-flying insects with the prothorax, mesothorax and elytra greatly reduced, the latter appearing as little, twisted strips, while the metathorax is relatively large, with its wings broad and capable of longitudinal folding. The feelers are branched and the jaws vestigial. The female is a segmented, worm-like creature, spending her whole life within the body of the bee, wasp or hug on which she is parasitic. One end of her body protrudes from between two of the abdominal segments of the host; it has been a subject of dispute whether this protruded end is the head or the tail, but there can be little doubt that it is the latter. While thus carried about by the host-insect, the female is fertilized by the free-flying male, and gives birth to a number of tiny triungulin larvae. The chief points in the life-history of Stylops and Xenos, which are parasitic on certain bees (Andrena) and wasps (Polistes), have been investigated by K. T. E. von Siebold (1843) and N. Nassonov (1892). The little triungulins escape on to the body of the bee or wasp; then those that are to survive must leave their host for a non-parasitized insect. Clinging to her hairs they are carried to the nest, where they bore into the body of a bee or wasp larva, and after a moult become soft-skinned legless maggots. The growth of the parasitic larva does not stop the development of the host-larva, and when the latter pupates and assumes the winged form, the stylopid, which has completed its transformation, is carried to the outer world. The presence of a Stylops causes derangement in the body of its host, and can he recognized by various external signs. Other genera of the family are parasitic on Hemiptera —bugs and frog-hoppers—but nothing is known as to the details of their life-history. I.AMELLICORNIA.—This is a very well-marked tribe of beetles, characterized by the peculiar elongation and flattening of three or more of the terminal antennal segments, so that the feeler seems to end in a number of leaf-like plates, or small comb-teeth (fig. 26, b, c). The wings are well developed for flight, and there is a tendency in the group, especially among the males, towards an excessive development of the mandibles or the presence of enormous, horn-like processes on the head or pronotum. There are four malpighian tubes. The larvae are furnished with large heads, powerful mandibles and well-developed legs, but the body-segments are feebly chitinized, and the tail-end is swollen. They feed in wood or spend an under-ground life devouring roots or animal excrement. The Lucanidae or stag beeties (figs. 1 and 25) have the terminal antennal segments pectinate, and so arranged that the comb-like part of the feeler cannot be curled up, while the elytra completely cover the abdomen. There are about 600 species in the family, the males being usually larger than the females, and remarkable for the size of their mandibles. In the same species, however, great variation occurs in the development of the mandibles, and the breadth of the head varies correspondingly, the smallest type of male being but little different in appearance from the female. The larvae of Lucanidae live within the wood of trees, and may take three or four years to attain their full growth. The Passalidae are a tropical family of beetles generally considered to be intermediate between stag-beetles and chafers, the enlarged segments of the feeler being capable of close approximation. The Scarabaeidae or chafers are an enormous family of about 15,000 species. The plate-like segments of the feeler (fig. 26, b, c) can be brought close together so as to form a club-like termination; usually the hinder abdominal segments are not covered by the elytra. In this family there is often a marked divergence between the sexes; the terminal antennal segments are larger in the male than in the female, and the males may carry large spinous processes on the head or prothorax, or both. These structures were believed by C. Darwin to he explicable by sexual selection. The larvae have the three pairs of legs well developed, and the hinder abdominal segments swollen. Most of the Scarabaeidae are vegetable-feeders, but one section VI. 22of the family—represented in temperate countries by the dorbeetles (Geotrupes) (fig. 28) and Aphodius, and in warmer regions by the " sacred " beetles of the Egyptians (Scarabaeus) (fig. 27), and allied genera—feed both in the adult and larval stages, on dung or decaying animal matter. The heavy grubs of Geotrupes, their Java. Antenna of male; c, antenna of female. swollen tail-ends black with the contained food-material, are often dug up in numbers in well-manured fields. The habits of Scarabaeus have been described in detail by J. H. Fabre. The female beetle in spring-time 'collects dung, which she forms into a ball by continuous rolling, sometimes assisted by a companion. This ball is buried in a suitable place, and serves the insect as a store of food. During summer the insects rest in their underground retreats, then inautumn Aegyptiorum. Africa. burnei. N. America. they reappear to bury another supply of dung, which serves as food for the larvae. Fabre states that the mother-insect carefully arranges the food-supply so that the most nutritious and easily digested portion is nearest the egg, to form the first meal of the young larva. In some species of Copris it is stated that the female S. America. W. Africa. lays only two or three eggs at a time, watching the offspring grow to maturity, andihen rearing another brood. Among the vegetable-feeding chafers we usually find that while the perfect insect devours leaves, the larva lives underground and feeds on roots. Such are the habits of the cockchafer (Melolontha vulgaris) and other species that often cause great injury to farm and II c b a garden crops (see CHAFER). Many of these insects, such as the species of Phanaeus (fig. 29) and Cetonia (fig. 30), are adorned with metallic or other brilliant colours. The African " goliath-beetles " (fig. 31) and the American " elephant-beetles " (Dynastes) are the largest of all insects. ANCHIsT0P0DA.—The families of beetles included by Kolbe in this group are distinguished by the possession of six malpighian tubes, and a great reduction in one or two of the tarsal segments, so that there seem to be only four or three segments in each foot; hence the names Tetramera and Trimera formerly applied to them. The larvae have soft-skinned bodies sometimes protected by rows of spiny tubercles, the legs being fairly developed in some families and greatlysegments to the foot, but there are really five, the fourth being greatly reduced. The mandibles are strong, adapted for biting the vegetable substances on which these beetles feed, and the palps of the second maxillae have three segments. Most of the Chrysomelidae are metallic in colour and convex in form; in some the head is concealed beneath the prothorax, and the so-called " tortoise " beetles (Cassidinae) have the elytra raised into a prominent median ridge. The most active form of larva found in this family resembles in shape that of a ladybird, tapering towards the tail end, and having the trunk segments protected by small firm sclerites. Such larvae, and also many with soft cuticle and swollen abdomen—those of the notorious " Colorado beetle," for example—feed openly reduced or absent in others. As might be expected, degeneration in larval structure is correlated with a concealed habit of life. The Coccinellidae, or ladybirds (fig. 32), are a large family of beetles, well known by their rounded convex bodies, usually shining and hairless. They have eleven segments to the feeler, which is clubbed at the tip, and apparently three segments only in each foot. Ladybirds are often brightly marked with spots and dashes, their coloration being commonly regarded as an advertisement of in-edibility. The larvae have a somewhat swollen abdomen, which is protected by bristle-bearing tubercles. Like the perfect insects, they are predaceous, feeding on plant-lice (Aphidae) and scale insects (Coccidae). Their role in nature is therefore beneficial to the cultivator. The Endomychidae (fig. 33), an allied family, are mostly fungus-eaters. In the Erotylidae and a few other small related families the feet are evidently four-segmented. The Chrysomelidae, or leaf-beetles (figs. 34, 35), are a very large family, with " tetramerous " tarsi; there seem to be only four on foliage. Others, with soft, white, cylindrical bodies, which recall the caterpillars of moths, burrow in the leaves or stems of plants. The larvae of the tortoise-beetles have the curious habit of forming an umbrella-like shield out of their own excrement, held in position by the upturned tail-process. The larvae of the beautiful, elongate, metallic Donaciae live in the roots and stems of aquatic plants, obtaining thence both food and air. The larva pierces the vessels of the plant with sharp processes at the hinder end of its body. In this way it is believed that the sub-aqueous cocoon in which the pupal stage is passed becomes filled with air. The Cerambycidae, or longhorn beetles, are recognizable by their slender, elongate feelers, which are never clubbed and rarely serrate. The foot has apparently four segments, as in the Chrysomelidae. The beetles are usually elongate and elegant in form, often adorned with bright bands of colour, and some of the tropical species attain a very large size (figs. 36, 37). The feelers are usually longer in the male than in the female, exceeding in some cases by many times the length of the body. The larvae have soft, fleshy bodies, with the head and prothorax large and broad, and the legs very much reduced. They live and feed in the wood of trees. Consequently, beetles of this family are most abundant in forest regions, and reach their highest development in the dense virgin forests of tropical countries, South America being particularly rich in peculiar genera. The Bruchidae, or seed-beetles, agree with the two preceding families in tarsal structure; the head is largely hidden by the pronotum, and the elytra are short enough to leave the end of the abdomen exposed (fig. 38). The development of the pea and bean-beetles has been carefully studied by C. V. Riley, who finds that the young larva, hatched from the egg laid on the pod, has three pairs of legs, and that these are lost after the moult that occurs when the grub has bored its way into the seed. In Great Britain the beetle, after completing its development, winters in the seed, waiting to emerge and lay its eggs on the blossom in the ensuing spring. (Pea Beetle.) Europe. latirostris. Europe. RHYxcHOPHORA.—The Rhynchophora are a group of beetles easily recognized by the elongation of the head into a beak or snout, which carries the feelers at its sides and the jaws at its tip. The third tarsal segment is broad and bi-lobed, and the fourth is so small that the feet seem to be only four-segmented. There are six malpighian tubes. The ventral scleriteof the head-skeleton (gula), well developed in most families of beetles, is absent among the Rhynchophora, while the palps of the maxillae are much reduced. The larvae have soft, white bodies and, with very few exceptions, no legs. Of the four families included in this group, the Anthribidae (fig. 39) have jointed, flexible palps, feelers—often of excessive length—with a short basal segment, and the three terminal segments forminga club, and, in some genera, larvae with legs. There are nearly 1000 known species, most of which live in tropical countries. The Brenthidae are a remarkable family almost confined to the tropics; they are elongate and narrow in form (fig. 40), with a straight, cylindrical snout which in some male beetles of the family is longer than the rest of the body. The Curculionidae, or weevils (q.v.), comprising 23,000 species, are by far the largest family of the group. The maxillary palps are short and rigid, and there is no distinct labrum, while the feelers are usually of an " elbowed " form, the basal segment being very elongate (figs. 41, 42). They are vegetable feeders, both in the perfect and larval stages, and are often highly injurious. The female uses her snout as a boring instrument to prepare a suitable place for egg-laying. The larvae (fig. 3) of some weevils live in seeds; others devour roots, while the parent-beetles eat leaves; others, again, are found in wood or under bark. The Scolytidae, or bark-beetles, are a family of some 1500 species, closely allied to the Curculionidae, differing only in the feeble development of the snout. They have clubbed feelers, and their cylindrical bodies (fig. 43) are well adapted for their burrowing habits under the bark of trees. Usually the mother-beetle makes a fairly straight tunnel along which, at short intervals, she lays her eggs. The grubs, when hatched, start galleries nearly at right angles to this, and when fully grown form oval cells in which they pupate; from these the young beetles emerge by making circular holes directly outward through the bark. The wings of Coleoptera (including the elytra) are described and discussed by F. Meinert (Entom. Tijdsk. v., 1880) ; C. Hoffbauer (Zeit. f. wissen. Zool. liv., 1892) ; J. H. Comstock and J. G. Needham (Amer. Nat. xxxii., 1898) ; and W. L. Tower (Zool. Jahrb. Anat. xvii., 1903). The morphology of the abdomen, ovipositor and genital armature is dealt with by K. W. Verhoeff (Ent. Nachtr. xx., 1894, and Arch. f. Naturg. lxi., lx11., 1895–1896) ; and B. Wandolleck (Zool. Jahrb. Anat. xxii., 1905). Luminous organs are described by H. von Wielowiejski (Zeits. f. wissen. Zool. xxxvii., 1882) ; C. Heinemann (Arch. f. mikr. Anat. xxvii., 1886) ; and R. Dubois (Bull. soc. zeol. France, 1886) ; and stridulating organs by C. J. Gahan (Trans. Entom. Soc., 1900). See also C. Darwin's Descent of Man and Selection in Relation to Sex (London, 1871). Many larvae of Coleoptera are described and beautifully figured by J. C. Schiodte (Naturh. Tidsskr. i.-xiii., 1861–1872). Hyper-metamorphosis in the Meloidae is described by G. Newport (Trans. Linn. Soc. xx., xxi., 1851–1853) ; C. V. Riley (Rep. U.S. Entom. Comm. i., 1878); J. H. Fabre (Ann. Sci. Nat. (4), ix., xix., 1848–1853) ; H. Beauregard (Les Insectes vesicants, Paris, 189o) ; and A. Chabaud (Ann. Soc. Ent. France, lx., 1891) ; in the Bruchidae by Riley (Insect Life, iv., v., 1892–1893; and in the Strepsiptera (Stylopidae) by K. T. E. von Siebold (Arch. f. Naturg. ix., 1843) ; N. Nassonov (Bull. Univ. Narsovie, 1892) ; and C. T. Brues (Zool. Jahrb. Anat. xiii., 1903). For various schemes of classification of the Coleoptera see E. L. Geoffroy (Insectes qui se trouvent aux environs de Paris, Paris, 1762) ; A. G. Olivier (Coleopteres, Paris, 1789--18o8); W. S. MacLeay (Annulosa Javanica, London, 1825) ; the general works of Westwood and Sharp, mentioned above; M. Gemminger and B. de Harold (Catalogus Coleopterorum, 12 vols., Munich, 1868–1872); T. Lacordaire and F. Chapuis (Genera des Coleopteres, to vols., Paris, 1854–1874) ; J. L. Leconte and G. H. Horn (Classification of Coleoptera of N. America, Washington, Smithsonian Inst., 1883); L. Ganglbauer (Die Keifer von Mitteleuropa, Vienna, 1892, &c.) ; A. Lameere (Ann. Soc. Ent. Belg. xliv., xxvii., 1900–1903) ; and H. J. Kolbe (Arch. f. Naturg. lxvii., 1901). For the British species, W. W. Fowler (Coleoptera of the British Islands, 5 vols., London, 1887–1891) is the standard work; and W. F. Johnson and J. N. Halbert's " Beetles of Ireland " (Prot. R. Irish Acad., 3, vi., 1902) is valuable faunistically. Among the large number of systematic writers on the order generally, or on special families, may be mentioned D. Sharp, T. V. Wollaston, H. W. Bates, G. C. Champion, E. Reitter, G. C. Crotch, H. S. Gorham, M. Jacoby, L. Fairmaire and C. O. Waterhouse. (G. H. C.)
End of Article: HETEROMERA
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