The common stag-beetle, Lucanus cervus, is our largest British beetle. The larva much resembles that of Melolontha vulgaris, but attains a larger size, and the anal aperture is placed longitudinally instead of transversely; it lives in decaying wood, or eats the roots of trees without being injurious; its life in this state lasts about four years; the pupal period is passed through rapidly, and the perfect Insect may remain for months underground before it becomes active; this occurs in June and July. This larva stridulates by scraping certain hard tubercular ridges on the third pair of legs, over a specially adapted rough area at the base of the second pair.
The Passalidae and Lucanidae are united by some authorities as a group called Pectinicornia; the term Lamellicornia being then confined to the Scarabaeidae. The Passalidae appear, however, to be really more nearly allied to the Scarabaeidae than to the Lucanidae.
Fam. 3. Scarabaeidae (Chafers).—The leaflets of the antennae are well coadapted, and are susceptible of separation. The elytra usually leave the pygidium uncovered. The number of visible ventral segments is usually six, or at the sides seven, not five, as in Lucanidae and Passalidae. This is one of the most important families of Insects. About 13,000 species are already known; as some of them are highly remarkable creatures on account of the males being armed with horns, they are figured in many works on natural history. There is great variety of form, and the following five sub-families may be adopted, though authorities are by no means agreed as to the classification of this extensive family, which, moreover, be it remarked, is increasing by the discovery of about 300 new species every year.
Abdominal spiracles placed in a line on the connecting membranes, and entirely covered by the wing-cases (Laparosticti). .......... Sub-fam. 1. Coprides.[[81]]
Abdominal spiracles placed almost in a line, but only the basal three on the connecting membranes; the terminal one usually not covered by the wing-cases. .......... Sub-fam. 2. Melolonthides.
Abdominal spiracles placed in two lines, the basal three on the connecting membranes, the others on the ventral segments (Pleurosticti).
The claws of the tarsi unequal. .......... Sub-fam. 3. Rutelides.
The claws of the tarsi equal; the front coxae transverse, but little prominent in the descending axis. .......... Sub-fam. 4. Dynastides.
The claws of the tarsi equal; the front coxae more prominent, shorter transversely. .......... Sub-fam. 5. Cetoniides.
i. The Coprides form an immense group of about 5000 species; they differ somewhat in habits from other Lamellicorns, inasmuch as most of them live on dung, or decaying animal matter; the sub-family connects with the Lucanidae, so far as superficial characters go, by means of two of its groups, Trogini and Nicagini, the latter being very near to the Ceratognathini in Lucanidae. So little is known as to the morphology and development of these groups that it is not possible to pronounce an opinion as to the validity of this apparent alliance. Trox stridulates by rubbing two raised lines on the penultimate dorsal segment across two striate ribs on the inner face of the elytra; Geotrupes, on the other hand, produces an audible sound by rubbing together a file on the posterior coxa and a fine ridge on the contiguous ventral segment. The larva in this genus has a different organ for stridulation from the imago; it is placed on the second and third pairs of legs, the latter pair being much reduced in size.