Fam. 9. Hydrometridae.—Form very diverse; antennae four-jointed, tarsi two-jointed. Coxae usually widely separated. Either wingless or with elytra of one texture throughout, having no membranous part. Under surface with a minute velvet-like pubescence. In many forms the legs are of great length.—Although of comparatively small extent—scarcely 200 species being at present known—this family is of great interest from the habit possessed by its members of living on the surface of water. In the case of the notorious genus Halobates (Fig. 265) the Insects can even successfully defy the terrors of Neptune and live on the ocean many hundreds of miles from land. There is great variety of form among Hydrometridae. The European and British genus Mesovelia is of short form, and but little dissimilar from ordinary land-bugs, with which, indeed, it is connected by means of the genus Hebrus, already noticed. Mesovelia represents the sub-family Mesoveliides, which, though consisting of only four species, occurs in both hemispheres, and in the tropics as well as in the temperate regions. Our species, M. furcata, walks on the surface of the water, the movements of its legs and the position of its coxae being those of land-bugs. Another British Insect—the highly remarkable Hydrometra stagnorum—is of excessively slender form, with long thin legs, by aid of which it walks on the surface-film of water, above which its body is held well separated. It is easily drowned, and if submerged it has great difficulty in escaping from the water. This genus represents the sub-family Hydrometrides, and is apparently almost cosmopolitan. Velia currens is another common British Insect; it loves the eddies and currents of backwaters on burns and streams, and is very abundant in Scotland. An American ally, Rhagovelia plumbea, appears to be not uncommon on the surface of the ocean in the Gulf of Mexico, near the shores. The great majority of the family belong to the division Gerrides, of which the curious, long Insects that float so lazily and skim so easily on the surface of quiet streams are typical. The species of the genus now called Gerris, but formerly known as Hydrometra are apparently distributed all over the world; we have ten in Britain. They have very long legs, and on being alarmed move away with the greatest ease.
The genus Halobates includes at present fifteen species. They are found on the ocean, where the surface-water is warm, in various parts of the world. They are destitute of any trace of alar organs, the meso- and meta-thorax are closely united and large, while the abdomen is very small, so that the body is of oval form; the middle legs are thrown so far back that they are placed immediately over the posterior pair. When the sea is calm these Insects skim over the surface with rapidity, but disappear as soon as it becomes agitated. They are believed to feed on small animals recently deceased; Witlaczil says on the juices of jelly-fish. The young are frequently met with, and there can be no doubt that the whole life-cycle may be passed through by the Insect far away from land. The Italian ship Vettor Pisani met with a bird's feather floating on the ocean off the Galapagos Islands, covered with eggs which proved to be those of Halobates in an advanced stage of development. It was formerly believed that the female carries the eggs for some time after their exclusion, and although this has since been denied, it is nevertheless an undoubted fact, for it was observed by Mr. J. J. Walker,[[488]] to whom we are indebted for a specimen having the eggs still attached to the body, as shown in Fig. 265. Mr. Walker believes the bugs shelter themselves when the sea is at all rough by keeping at a sufficient distance below the surface; they can dive with facility, and are gregarious. They are frequently found close to the shore, and Mr. Walker has even met with them on land. The stink-glands of other Hemiptera are said by Nassonoff to be replaced in Halobates by peculiar ventral glands. An allied genus, Halobatodes, was supposed to be oceanic, but this is not the case, some of the species having been found recently in fresh water in India, and others in estuaries at Port Darwin. A remarkable allied form, Hermatobates haddoni, was recently discovered by Professor Haddon in Torres Straits. Apart from the oceanic life, Halobates is by no means the most extraordinary of the Hydrometridae. The Javanese Ptilomera laticaudata repeats some of its peculiarities, and is of larger size, with the sexes very different. The most remarkable of the family is perhaps the fresh-water genus Rheumatobates (Fig. 266), in which the males have peculiar prehensile antennae that look like legs. These curious Insects inhabit North America and the West Indies.
Fig. 266—Rheumatobates bergrothi. × 10. West Indies. (After Meinert.)
We may here notice an enigmatic Insect called Hemidiptera haeckeli by Léon. From the single specimen known it is concluded that the Insect has only one pair of wings, and that they are attached to the metathorax. It is, however, possible, as suggested by Bergroth,[[489]] that the anterior pair have been detached by some accident.
Fam. 10. Henicocephalidae.—Head swollen behind the eyes so as to form a sort of globe, on the anterior part of which the ocelli are placed. Rostrum extremely short. Elytra rather large, of one consistence throughout; conspicuously veined.—There is only one genus; it is very widely distributed, about a dozen species being known; one of these occurs in the south of Europe. These curious little bugs appear to be most nearly allied to the Reduviidae. According to Westwood and others they are somewhat gregarious; a Tasmanian species dances in the air after the fashion of midges or May-flies, and dispenses an agreeable, musk-like odour.
Fig. 267—Carcinocoris binghami (Phymatidae). Burma.
Fam. 11. Phymatidae.—Front legs of peculiar structure, short and stout, with long coxae, short thick femora, and tibiae curvate, pointed; frequently without tarsi.—The Insects of this family are believed to be predaceous, the structure of the legs being such as is called raptorial, and one species, Phymata erosa, being known to capture and suck honey-bees in North America. There are only about seventy species of Phymatidae known. We have none in Britain, though there are a few in Southern Europe; one of these, P. crassipes, extends as far north as Paris. The distinction of the family from Reduviidae is doubtful.[[490]] There are a few very rare forms (Fig. 267) in which the front tibia is articulated to the femur in such a way that a pair of pincers is formed: the tarsus is in this form, as well as in some other Phymatidae, absent.
