Fam. 58. Dascillidae.—Small or moderate-sized beetles, with rather flimsy integuments, antennae either serrate, filiform, or even made flabellate by long appendages; front coxae elongate, greatly exserted; abdomen with five mobile ventral segments; tarsi five-jointed. This is one of the most neglected and least known of all the families of Coleoptera, and one of the most difficult to classify; though always placed amongst the Serricornia, it is more nearly allied to Parnidae and Byrrhidae, that are placed in Clavicornia, than it is to any of the ordinary families of Serricornia. It is probable that careful study will show that it is not natural as at present constituted, and that the old families, Dascillidae and Cyphonidae, now comprised in it, will have to be separated. Only about 400 species are at present known; but as nearly 100 of these have been detected in New Zealand, and 17 in Britain, doubtless the numbers in other parts of the world will prove very considerable, these Insects having been neglected on account of their unattractive exterior, and fragile structure. The few larvae known are of three or four kinds. That of Dascillus cervinus is subterranean, and is believed to live on roots; in form it is somewhat like a Lamellicorn larva, but is straight, and has a large head. Those of the Cyphonides are aquatic, and are remarkable for possessing antennae consisting of a great many joints (Fig. 132, A). Tournier describes the larva of Helodes as possessing abdominal but not thoracic spiracles, and as breathing by coming to the surface of the water and carrying down a bubble of air adhering to the posterior part of the body; the larva of Hydrocyphon (Fig. 132, A) possesses several finger-like pouches that can be exstulpated at the end of the body. It is probable that these larvae are carnivorous. The imago of this Insect abounds on the bushes along the banks of some of the rapid waters of Scotland; according to Tournier, when alarmed, it enters the water and goes beneath it for shelter. The third form of larva belongs to the genus Eucinetus, it lives on fungoid matter on wood, and has ordinary antennae of only four joints.[[132]] It is very doubtful whether Eucinetus is related to other Dascillidae; some authorities indeed place it in Silphidae.
Fam. 59. Rhipiceridae.—Tarsi five-jointed, furnished with a robust onychium (a straight chitinous process bearing hairs) between the claws; antennae of the male bearing long processes, and sometimes consisting of a large number of joints. Mandibles robust, strongly curved, and almost calliper-like in form. This small family of less than 100 species is widely distributed, though confined to the warmer regions of the earth, a single species occurring in the extreme south of Eastern Europe. Very little is known as to the natural history. The larva of Callirhipis dejeani (Fig. 133, A) is described by Schiödte as hard, cylindrical in form, and peculiarly truncate behind, so that there appear to be only eight abdominal segments, the ninth segment being so short as to look like an operculum at the extremity of the body. It lives in wood.
Fig. 133—A, Larva of Callirhipis dejeani (after Schiödte); B, Rhipicera mystacina male, Australia; C, under side of its hind foot.
Fig. 134—Athous rhombeus. New Forest. A, Larva; B, female imago.
Fam. 60. Elateridae (Click-beetles).—Antennae more or less serrate along the inner margin, frequently pectinate, rarely filiform. Front coxae small, spherical. Thorax usually with hind angles more or less prolonged backwards; with a prosternal process that can be received in, and usually can move in, a mesosternal cavity. Hind coxa with a plate, above which the femur can be received. Visible ventral segments usually five, only the terminal one being mobile. Tarsi five-jointed. This large family of Coleoptera comprises about 7000 species. Most of them are readily known by their peculiar shape, and by their faculty of resting on the back, stretching themselves out flat, and then suddenly going off with a click, and thus jerking themselves into the air. Some, however, do not possess this faculty, and certain of these are extremely difficult to recognise from a definition of the family. According to Bertkau[[133]] our British Lacon murinus is provided near the tip of the upper side of the abdomen with a pair of eversible glands, comparable with those that are better known in Lepidopterous larvae. He states that this Insect does not try to escape by leaping, but shams death and "stinks away" its enemy. The glands, it would appear, become exhausted after the operation has been repeated many times. The extent of the leap executed by click-beetles differs greatly; in some species it is very slight, and only just sufficient to turn the Insect right side up when it has been placed on its back. In some cases the Insects go through the clicking movements with little or no appreciable result in the way of consequent propulsion. Although it is difficult to look on this clicking power as of very great value to the Elateridae, yet their organisation is profoundly modified so as to permit its accomplishment. The junction of the prothorax with the after-body involves a large number of pieces which are all more or less changed, so that the joint is endowed with greater mobility than usual; while in the position of repose, on the other hand, the two parts are firmly locked together. The thoracic stigma is of a highly remarkable nature, and the extensive membrane in which it is placed appears to be elastic. Although the mechanics of the act of leaping are still obscure, yet certain points are clear; the prosternal process possesses a projection, or notch, on its upper surface near the tip; as a preliminary to leaping, this projection catches against the edge of the mesosternal cavity, and as long as this position is maintained the Insect is quiescent; suddenly, however, the projection slips over the catch, and the prosternal process is driven with force and rapidity into the mesosternal cavity pressing against the front wall thereof, and so giving rise to the leap.
Several larvae are well known; indeed the "wire-worms" that are sometimes so abundant in cultivated places are larvae of Elateridae. In this instar the form is usually elongate and nearly cylindrical; the thoracic segments differ but little from the others except that they bear rather short legs; the skin is rather hard, and usually bears punctuation or sculpture; the body frequently terminates in a very hard process, of irregular shape and bearing peculiar sculpture on its upper surface, while beneath it the prominent anal orifice is placed: this is sometimes furnished with hooks, the function of which has not yet been observed. The majority of these larvae live in decaying wood, but some are found in the earth; as a rule the growth is extremely slow, and the life of the larva may extend over two or more years. Some obscurity has prevailed as to their food; it is now considered to be chiefly flesh, though some species probably attack decaying roots; and it is understood that wire-worms destroy the living roots, or underground stems, of the crops they damage. Various kinds of Myriapods (see Vol. V. p. 29) are often called "wire-worm," but they may be recognised by possessing more than six legs. The larvae of the genus Cardiophorus are very different, being remarkably elongate without the peculiar terminal structure, but apparently composed of twenty-three segments.
The genus Pyrophorus includes some of the most remarkable of light-giving Insects. There are upwards of 100 species, exhibiting much diversity as to the luminous organs; some are not luminous at all; but all are peculiar to the New World, with the exception that there may possibly be luminous species, allied to the American forms, in the Fiji Islands and the New Hebrides. In the tropics of America the Pyrophorus, or Cucujos, form one of the most remarkable of the natural phenomena. The earliest European travellers in the New World were so impressed by these Insects that descriptions of their wondrous display occupy a prominent position in the accounts of writers like Oviedo, whose works are nearly 400 years old. Only one of the species has, however, been investigated. P. noctilucus is one of the most abundant and largest of the Pyrophorus, and possesses on each side of the thorax a round polished space from which light is given forth; these are the organs called eyes by the older writers. Besides these two eye-like lamps the Insect possesses a third source of light situate at the base of the ventral surface of the abdomen; there is no trace of this latter lamp when the Insect is in repose; but when on the wing the abdomen is bent away from the breast, and then this source of light is exposed; hence, when flying, this central luminous body can be alternately displayed and concealed by means of slight movements of the abdomen. The young larva of P. noctilucus is luminous, having a light-giving centre at the junction of the head and thorax; the older larva has also numerous luminous points along the sides of the body near the spiracles. It is remarkable that there should be three successive seats of luminescence in the life of the same individual. The eggs too are said to be luminous. The light given off by these Insects is extremely pleasing, and is used by the natives on nocturnal excursions, and by the women for ornament. The structure of the light-organs is essentially similar to that of the Lampyridae. The light is said to be the most economical known; all the energy that is used being converted into light, without any waste by the formation of heat or chemical rays. The subject has been investigated by Dubois,[[134]] who comes, however, to conclusions as to the physiology of the luminous processes different from those that have been reached by Wielowiejski and others in their investigations on Glow-worms. He considers that the light is produced by the reactions of two special substances, luciferase and luciferine. Luciferase is of the nature of an enzyme, and exists only in the luminous organs, in the form, it is supposed, of extremely minute granules. Luciferine exists in the blood; and the light is actually evoked by the entry of blood into the luminous organ.
We have given to this family the extension assigned to it by Schiödte. Leconte and Horn also adopt this view, except that they treat Throscides as a distinct family. By most authors Eucnemides, Throscides, and Cebrionides are all considered distinct families, but at present it is almost impossible to separate them on satisfactory lines. The following table from Leconte and Horn exhibits the characters of the divisions so far as the imago is concerned:—