Chernetidea are not creatures which obtrude themselves on the general notice, and it is highly probable that many readers have never seen a living specimen. This is largely due to their minute size. Garypus littoralis, a Corsican species, nearly a quarter of an inch in length of body, is a veritable giant of the tribe, while no British species boasts a length of more than one-sixth of an inch.
Moreover, their habits are retiring. They are to be sought for under stones, under the bark of trees, and among moss and débris. One species, probably cosmopolitan, certainly lives habitually in houses, and is occasionally noticed and recognised as the “book-scorpion,” and one or two other species sometimes make themselves conspicuous by the remarkable habit of seizing hold of the legs of flies and being carried about with them in their flight. With these exceptions, the Chernetidea are not likely to be seen unless specially sought for, or unless casually met with in the search for small beetles or other creatures of similar habitat. Nevertheless they are very widely distributed, and though more numerous in hot countries, are yet to be found in quite cold regions.
Though comparatively little attention has been paid to them in this country, twenty British species have been recorded, and the known European species number about seventy.
As might be expected from their small size and retiring habits, little is known of their mode of life. They are carnivorous, feeding apparently upon any young insects which are too feeble to withstand their attacks. The writer has on two or three occasions observed them preying upon Homopterous larvae. As a rule they are sober-coloured, their livery consisting of various shades of yellow and brown. Some species walk slowly, with their relatively enormous pedipalps extended in front and gently waving, but all can run swiftly backwards and sideways, and in some forms the motion is almost exclusively retrograde and very rapid. A certain power of leaping is said to be practised by some of the more active species. The Chernetidea possess spinning organs, opening on the movable digit of the chelicera. They do not, however, spin snares like the Spiders, nor do they anchor themselves by lines, the sole use of the spinning apparatus being, apparently, to form a silken retreat at the time of egg-laying or of hibernation.
External Structure.—The Chernetid body consists of a cephalothorax, and an abdomen composed of twelve segments. The segmentation of the abdomen is emphasised by the presence of chitinous plates dorsally and ventrally, but the last two dorsal plates and the last four ventral plates are fused, so that ordinarily only eleven segments can be counted above and nine below.
The cephalothorax presents no trace of segmentation in the Obisiinae (see p. [437]), but in the other groups it is marked dorsally with one or two transverse striae. The eyes, when present, are either two or four in number, and are placed near the lateral borders of the carapace towards its anterior end. They are whitish and only very slightly convex, and are never situated on prominences. Except in Garypus there is no trace of a sternum, the coxae of the legs and pedipalps forming the ventral floor of the cephalothorax.
In the Obisiinae a little triangular projection in front of the cephalothorax is regarded by Simon[[333]] as an epistome. It is absent in the other sub-orders.
The abdomen is armed, dorsally and ventrally, with a series of chitinous plates with membranous intervals. The dorsal plates are eleven in number (except in Chiridium, which has only ten), and are frequently bisected by a median dorsal membranous line. There are nine ventral plates. There is a membranous interval down each side between the dorsal and ventral series of plates.
Fig. [222].—A, Chernes sp., diagrammatic ventral view, × about 12. a, Anus; ch, chelicera; g, generative opening; p, pedipalp; 1, 2, 3, 4, legs. (The stigmata are at the postero-lateral margins of the 1st and 2nd abdominal segments.) B, Tarsus, with claws and sucking disc.