Fam. 15. Silphidae.—The mentum is usually a transverse plate, having in front a membranous hypoglottis, which bears the exposed labial palpi, and immediately behind them the so-called bilobed ligula. The anterior coxae are conical and contiguous: prothoracic epimera and episterna not distinct. Visible abdominal segments usually five, but sometimes only four, or as many as seven. Tarsi frequently five-jointed, but often with one joint less. Elytra usually covering the body and free at the tips, but occasionally shorter than the body, and even truncate behind so as to expose from one to four of the dorsal plates; but there are at least three dorsal plates in a membranous condition at the base of the abdomen. These beetles are extremely diverse in size and form, some being very minute, others upwards of an inch long, and there is also considerable range of structure. In this family are included the burying-beetles (Necrophorus), so well known from their habit of making excavations under the corpses of small Vertebrates, so as to bury them. Besides these and Silpha, the roving carrion-beetles, the family includes many other very different forms, amongst them being the larger part of the cave-beetles of Europe and North America. These belong mostly to the genera Bathyscia in Europe, and Adelops in North America; but of late years quite a crowd of these eyeless cave-beetles of the group Leptoderini have been discovered, so that the European catalogue now includes about 20 genera and 150 species. The species of the genus Catopomorphus are found in the nests of ants of the genus Aphaenogaster in the Mediterranean region. Scarcely anything is known as to the lives of either the cave-Silphidae or the myrmecophilous forms.
The larvae of several of the larger forms of Silphidae are well known, but very little has been ascertained as to the smaller forms. Those of the burying-beetles have spiny plates on the back of the body, and do not resemble the other known forms of the family. The rule is that the three thoracic segments are well developed, and that ten abdominal segments are also distinct; the ninth abdominal segment bears a pair of cerci, which are sometimes elongate. Often the dorsal plates are harder and better developed than is usual in Coleopterous larvae. This is especially the case with some that are endowed with great powers of locomotion, such as S. obscura (Fig. 104). The food of the larvae is as a rule decomposing animal or vegetable matter, but some are predaceous, and attack living objects. The larger Silpha larvae live, like the Necrophorus, on decomposing animal matter, but run about to seek it; hence many specimens of some of these large larvae may sometimes be found amongst the bones of a very small dead bird. We have found the larva and imago of S. thoracica in birds' nests containing dead nestlings. S. atrata and S. laevigata make war on snails. S. lapponica enters the houses in Lapland and ravages the stores of animal provisions. S. opaca departs in a very decided manner from the habits of its congeners, as it attacks beetroot and other similar crops in the growing state; it is sometimes the cause of serious loss to the growers of beet. The larvae of the group Anisotomides are believed to be chiefly subterranean in habits; that of A. cinnamomea feeds on the truffle, and the beetle is known as the truffle-beetle.
Fig. 104—A, Larva of Silpha obscura. Europe. (After Schiödte). B, Ptomaphila lacrymosa, Australia.
The number of species of Silphidae known must be at present nearer 900 than 800. Of these an unusually large proportion belong to the European and North American regions; Silphidae being apparently far from numerous in the tropics. Rather more than 100 species are natives of Britain. The family reappears in considerable force in New Zealand, and is probably well represented in South Australia and Tasmania. The most remarkable form known is perhaps the Australian genus Ptomaphila (Fig. 104, B). The classification of the family is due to Dr. Horn.[[101]] The only change of importance that has since been suggested is the removal of Sphaerites from this family to Synteliidae. Anisotomidae and Clambidae have been considered distinct families, but are now included in Silphidae.
Fam. 16. Scydmaenidae.—Minute Insects allied to Silphidae, but with the hind coxae separated, and the facets of the eyes coarser; the tarsi are five-jointed; the number of visible abdominal segments is six. These small beetles are widely spread over the earth's surface, and about 700 species are now known, of which we have about a score in Britain; many live in ants' nests, but probably usually rather as intruders than as guests that have friendly relations with their hosts. Nothing is known as to their life-histories, but the food of the imago, so far as is known, consists of Acari. Mastigus is a very aberrant form, found in moss and dead leaves in Southern Europe. By means of Brathinus the family is brought very near to Silphidae; Casey, however, considers Brathinus to belong to Staphylinidae rather than to Scydmaenidae. The South European Leptomastax is remarkable on account of the slender, long, sickle-shaped mandibles. The Oriental genus Clidicus is the largest and most remarkable form of the family; it has a very slender neck to its broad head, and is more than a quarter of an inch long.
Fam. 17. Gnostidae.—Minute Insects with three-jointed antennae, five-jointed tarsi, and three apparent ventral segments, the first of which, however, is elongate, and consists of three united plates. Elytra entirely covering the after-body. The family consists of two species which have been found in the nests of ants, of the genus Cremastogaster, in Brazil.[[102]]
Fam. 18. Pselaphidae.—Very small Insects; the elytra much abbreviated, usually leaving as much as half the abdomen uncovered; the maxillary palpi usually greatly developed, and of a variety of remarkable forms; the segments of the abdomen not more than seven in number, with little or no power of movement. Tarsi with not more than three joints. These small Coleoptera mostly live in the nests of ants, and present a great diversity of extraordinary shapes, and very peculiar structures of the antennae and maxillary palpi. Owing to the consolidation of some of its segments, the abdomen frequently appears to have less than the usual number. In the curious sub-family Clavigerides, the antennae may have the joints reduced to two or even, to all appearance, to one; the tarsi suffer a similar reduction. There are about 2500 species of Pselaphidae known; many of them have never been found outside the ants' nests; very little, however, is known as to their natural history. It is certain that some of them excrete, from little tufts of peculiar pubescence, a substance that the ants are fond of. The secretory patches are found on very different parts of the body and appendages. Claviger testaceus is fed by the ants in the same way as these social Insects feed one another; the Claviger has also been seen to eat the larvae of the ants. They ride about on the backs of the ants when so inclined. The family is allied to Staphylinidae, but is easily distinguished by the rigid abdomen. Only one larva—that of Chennium bituberculatum—is known. It appears to be very similar to the larvae of Staphylinidae. The best account of classification and structure is that given by M. Achille Raffray,[[103]] who has himself discovered and described a large part of the known species.
Fam. 19. Staphylinidae.—Elytra very short, leaving always some of the abdominal segments exposed, and covering usually only two of the segments. Abdomen usually elongate, with ten dorsal, and seven or eight ventral segments; of the latter six or seven are usually exposed; the dorsal plates as hard as the ventral, except sometimes in the case of the first two segments; the segments very mobile, so that the abdomen can be curled upwards. The number of tarsal joints very variable, often five, but frequently as few as three, and not always the same on all the feet. Staphylinidae (formerly called Brachelytra or Microptera) is one of the most extensive of even the great families of Coleoptera; notwithstanding their diversity, they may in nearly all cases be recognised by the more than usually mobile and uncovered abdomen, combined with the fact that the parts of the mouth are of the kind we have mentioned in Silphidae. The present state of the classification of this family has been recently discussed by Ganglbauer.[[104]]
