The larvae are much more active than beetle-larvae usually are, and many of them are very conspicuous when running about on plants to hunt their prey. They usually cast their skins three times, and sometimes concomitantly change a good deal in colour and form; the larval life does not usually exceed four or five weeks; at the end of which time the larva suspends itself by the posterior extremity, which is glued by a secretion to some object; the larval skin is pushed back to the anal extremity, disclosing the pupa; this differs in several respects from the usual pupa of beetles; it is harder, and is coloured, frequently conspicuously spotted, and dehisces to allow the escape of the beetle, so that the metamorphosis is altogether more like that of Lepidoptera than that of Coleoptera. There is much variety in the larvae; some of them bear large, complexly-spined, projections; those of the group Scymnites have small depressions on the surface, from which it has been ascertained that waxy secretions exude; but in Scymnus minimus no such excretions are formed. Certain species, when pupating, do not shuffle the skin to the extremity of the body, but retain it as a covering for the pupa. The larvae that feed on plants are much less active than the predaceous forms. We are well supplied with Coccinellidae in Britain, forty species being known here.
The systematic position of Coccinellidae amongst the Coleoptera has been for long a moot point. Formerly they were associated with various other beetles having three-jointed, or apparently three-jointed, feet, as a series with the name Trimera, or Pseudotrimera. But they are generally placed in the Clavicorn series, near Endomychidae. Verhoeff has recently made considerable morphological studies on the male genital organs of Coleoptera, and as the result, he concludes that Coccinellidae differ radically from all other Coleoptera as regards these structures, and he therefore treats them as a distinct series or sub-order, termed Siphonophora. The genus Lithophilus has been considered doubtfully a member of Coccinellidae, as the tarsi possess only in a slight degree the shape characteristic of the family: Verhoeff finds that they are truly Coccinellidae, forming a distinct division, Lithophilini; and our little species of Coccidula, which have somewhat the same appearance as Lithophilini, he treats as another separate group, Coccidulini.
Fam. 39. Endomychidae.[[122]]—Tarsi apparently three-jointed, the first two joints broad, the terminal joint elongate; at the base of the terminal joint there is, however, a very small joint, so that the tarsi are pseudotetramerous; antennae rather large, with a large club; labium not at all retracted behind the mentum; front and middle coxae globose; abdomen with five movable ventral segments, and a sixth more or less visible at the tip. This family includes a considerable diversity of elegant Insects that frequent fungoid growths on wood. It comprises at present fully 500 species, but nearly the whole of them are exotic, and inhabit the tropical forests. We have only two British species, both of which are now rarities, but apparently were much commoner at the beginning of the century. The larvae are broader than is usual in Coleoptera; very few, however, are known.
Fig. 119—Mycetaea hirta. Britain. A, Larva (after Blisson); B, perfect Insect.
Fam. 40. Mycetaeidae.—Tarsi four-jointed, the first two joints not very different from the third, usually slender; abdomen with five visible ventral segments, which are movable; front and middle coxae globular. The little Insects composing this family are by many placed as a division of Endomychidae, and Verhoeff is of opinion that the group is an altogether artificial one; but we think, with Duval, it makes matters simpler to separate them. There are only some forty or fifty species, found chiefly in Europe and North America. We have three in Britain; one of these, Mycetaca hirta is very common, and may be found in abundance in cellars in the heart of London, as well as elsewhere; it is said to have injured the corks of wine-bottles, and to have caused leakage of the wine, but we think that it perhaps only increases some previous deficiency in the corkage, for its natural food is fungoid matters. The larva is remarkable on account of the clubbed hairs at the sides of the body.
Fam. 41. Latridiidae.—Tarsi three-jointed; anterior coxal cavities round, not prolonged externally; abdomen with five visible and mobile ventral segments. Very small Insects, species of which are numerous in most parts of the world, the individuals being sometimes very abundant. The larvae (Fig. 120, A) are said by Perris to have the mandibles replaced by fleshy appendages. The pupa of Latridius is remarkable, on account of the numerous long hairs with heads instead of points; the larva of Corticaria is very like that of Latridius, but some of the hairs are replaced by obconical projections. The sub-family Monotomides is by many treated as a distinct family; they have the elytra truncate behind, exposing the pygidium, and the coxae are very small and very deeply embedded. Most of the Latridiidae are believed to live on fungoid matters; species of Monotoma live in ants' nests, but probably have no relations with the ants. A few species of Latridiides proper also maintain a similar life; Coluocera formicaria is said to be fond of the stores laid up by Aphaenogaster structor in its nests. About 700 species are now known; scarcely any of the individuals are more than one-tenth of an inch long. We have about 40 species in Britain. The North American genus Stephostethus has the prosternum constructed behind the coxae, somewhat in the same manner as it is in the Rhynchophorous series of Coleoptera.
Fig. 120—Latridius minutus. Britain. A, Larva (after Perris); B, perfect Insect.
Fam. 42. Adimeridae.—Tarsi appearing only two-jointed, a broad basal joint and an elongate claw-bearing joint, but between the two there are two very small joints. This family consists only of the American genus Adimerus; nothing is known of the life-history of these small Insects. They are of some interest, as this structure of the foot is not found in any other beetles.