Fig. 224—Head of Bibio. × 10. A, Of male, seen from the front; C, from the side; a, upper, b, lower eye; B, head of female.
Fam. 10. Bibionidae.—Flies of moderate or small size, sometimes of different colours in the two sexes, with short, thick, straight, antennae; front tibiae usually with a long pointed process; coxae not elongate. Eyes of male large, united, or contiguous in front. The flies of the genus Bibio usually appear in England in the spring, and are frequently very abundant; they are of sluggish habits and poor performers on the wing.
Fig. 225—Larva of Bibio sp. Cambridge. × 5.
The difference in colour of the sexes is very remarkable, red or yellow predominating in the female, intense black in the male; and it is a curious fact that the same sexual distinction of colour reappears in various parts of the world—England, America, India, and New Zealand; moreover, this occurs in genera that are by no means closely allied, although allied species frequently have concolorous sexes. The eyes of the males are well worth study, there being a very large upper portion, and, abruptly separated from this, a smaller, differently faceted lower portion, practically a separate eye; though so largely developed the upper eye is in some cases so hairy that it must greatly interfere with the formation of a continuous picture. Carrière considers that the small lower eye of the male corresponds to the whole eye of the female. The larvae of Bibio (Fig. 225) are caterpillar-like in form, have a horny head, well developed, biting mouth-organs, and spine-like processes on the body-segments. They are certified by good authorities[[394]] to possess the extremely unusual number of ten pairs of spiracles; a larva found at Cambridge, which we refer to Bibio (Fig. 225) has nine pairs of moderate spiracles, as well as a large terminal pair separated from the others by a segment without spiracles. The genus Dilophus is closely allied to Bibio, the larvae of which (and those of Bibionidae in general) are believed to feed on vegetable substances; the parasitism of Dilophus vulgaris on the larva of a moth, Epinotia (Chaetoptria) hypericana, as recorded by Meade,[[395]] must therefore be an exceptional case. In the genus Scatopse there is a very important point to be cleared up as to the larval respiratory system; it is said by Dufour and Perris[[396]] to be amphipneustic; there are, however, nine projections on each side of the body that were considered by Bouché, and probably with good reason, to be spiracles. The food of Scatopse in the larval state is principally vegetable. The larva of Scatopse changes to a pupa inside the larval skin; the pupa is provided on the thorax with two branched respiratory processes that project outside the larval skin.[[397]] Lucas has given an interesting account of the occurrence of the larva of Bibio marci in enormous numbers at Paris; they lived together in masses, there being apparently some sort of connection between the individuals.[[398]] In the following year the fly was almost equally abundant.
Fig. 226—Portion of integument of Bibio sp. Cambridge. p, Intersegmental processes; s, spiracle.
Owing to the great numbers in which the species of Bibionidae sometimes appear, these Insects have been supposed to be very injurious. Careful inquiry has, however, generally exculpated them as doers of any serious injury, though Dilophus febrilis—a so-called fever-fly—appears to be really injurious in this country when it multiplies excessively, by eating the roots of the hop-plant.
Fam. 11. Simuliidae (Sand-flies, Buffalo-gnats).—Small obese flies with humped back, rather short legs and broad wings, with short, straight antennae destitute of setae; proboscis not projecting. There is only one genus, Simulium, of this family, but it is very widely spread, and will probably prove to be nearly cosmopolitan. Some of the species are notorious from their blood-sucking habits, and in certain seasons multiply to an enormous extent, alight in thousands on cattle, and induce a disease that produces death in a few hours; it is thought as the result of an instilled poison. S. columbaczense has occasioned great losses amongst the herds near the Danube; in North America the Buffalo- and Turkey-gnats attack a variety of mammals and birds. In Britain and other parts of the world they do not increase in numbers to an extent sufficient to render them seriously injurious: their bite is however very annoying and irritating to ourselves. In their early stages they are aquatic and require well aërated waters: the larvae hold themselves erect, fixed to a stone or some other object by the posterior extremity, and have on the head some beautiful fringes which are agitated in order to bring food within reach; the pupae are still more remarkable, each one being placed in a pouch or sort of watch-pocket, from which projects the upper part of the body provided with a pair of filamentous respiratory processes. For an account of the interesting circumstances connected with the metamorphoses of this species the reader should refer to Professor Miall's book; and for the life-history of the American Buffalo-gnat to Riley.[[399]]
Fam. 12. Rhyphidae.—This is another of the families that have only two or three genera, and yet are very widely distributed. These little flies are distinguished from other Nemocera Anomala (cf. p. [456]) by the presence of a discal cell; the empodia of the feet are developed as if they were pulvilli, while the true pulvilli remain rudimentary. The larvae are like little worms, being long and cylindric; they are amphipneustic, and have been found in decaying wood, in cow-dung, in rotten fruits, and even in dirty water. The "petite tipule," the metamorphoses of which were described and figured by Réaumur, is believed to be the common Rhyphus fenestralis.[[400]] R. fenestralis is often found on windows, as its name implies.