No generalisation can yet be made as to the larvae of these divisions, neither can any characters be pointed out by which they can be distinguished from the larvae of the following families. In their habits they have nothing specially distinctive, and may be said to resemble the Anthomyiidae, vegetable matter being more used as food than animal; many of them mine in the leaves or stems of plants; in the genus Dorycera the larva is aquatic, mining in the leaves of water-plants, and in Ephydridae several kinds of aquatic larvae are found, some of which are said to resemble the rat-tailed larvae of Syrphidae; certain of these larvae occur in prodigious quantities in lakes, and the Insects in some of their early stages serve the Mexicans as food, the eggs being called Ahuatle, the larvae Pusci, the pupae Koo-chah-bee. Some of the larvae of the Sciomyzidae are also aquatic: that of Tetanocera ferruginea is said by Dufour to consist only of eight segments, and to be metapneustic; Brauer considers the Acalyptrate larvae to be, however, in general, amphipneustic, like those of Calyptratae. The Chloropidae are a very important family owing to their occasional excessive multiplication, and to their living on cereals and other grasses, various parts of which they attack, sometimes causing great losses to the agriculturist. The species of the genus Chlorops are famous for the curious habit of entering human habitations in great swarms: frequently many millions being found in a single apartment. Instances of this habit have been recorded both in France and England, Cambridge being perhaps the place where the phenomenon is most persistently exhibited. In the year 1831 an enormous swarm of C. lineata was found in the Provost's Lodge at King's College and was recorded by Leonard Jenyns; in 1870 another swarm occurred in the same house if not in the same room.[[428]] Of late years such swarms have occurred in certain apartments in the Museums (which are not far from King's College), and always in the same apartments. No clue whatever can be obtained as to their origin; and the manner in which these flies are guided to a small area in numbers that must be seen to be believed, is most mysterious. These swarms always occur in the autumn, and it has been suggested that the individuals are seeking winter quarters.
Fig. 241—Celyphus (Paracelyphus) sp. West Africa. A, The fly seen from above; a, scutellum; b, base of wing: B, profile, with tip of abdomen bent downwards; a, scutellum; b, b, wing; c, part of abdomen.
Several members of the Acalyptratae have small wings or are wingless, as in some of our species of Borborus. The Diopsidae—none of which are European—have the sides of the head produced into long horns, at the extremity of which are placed the eyes and antennae; these curiosities (Fig. 240) are apparently common in both Hindostan and Africa. In the horned flies of the genus Elaphomyia, parts of the head are prolonged into horns of very diverse forms according to the species, but bearing on the whole a great resemblance to miniature stag-horns. A genus (Giraffomyia) with a long neck, and with partially segmented appendages, instead of horns on the head, has been recently discovered by Dr. Arthur Willey in New Britain. Equally remarkable are the species of Celyphus; they do not look like flies at all, owing to the scutellum being inflated and enlarged so as to cover all the posterior parts of the body as in the Scutellerid Hemiptera: the wings are entirely concealed, and the abdomen is reduced to a plate, with its orifice beneath, not terminal; the surface of the body is highly polished and destitute of bristles. Whether this is a mimetic form, occurring in association with similar-looking Bugs is not known. The North American genus Toxotrypana is furnished with a long ovipositor; and in this and in the shape of the body resembles the parasitic Hymenoptera. This genus was placed by Gerstaecker in Ortalidae, but is considered by later writers to be a member of the Trypetidae. This latter family is of considerable extent, and is remarkable amongst the Diptera for the way in which the wings of many of its members are ornamented by an elaborate system of spots or marks, varying according to the species.
Fam. 34. Anthomyiidae.—Flies similar in appearance to the House-fly; the main vein posterior to the middle of the wing (4th longitudinal) continued straight to the margin, not turned upwards. Eyes of the male frequently large and contiguous, bristle of antenna either feathery or bare. This very large family of flies is one of the most difficult and unattractive of the Order. Many of its members come close to the Acalyptrate Muscidae from which they are distinguished by the fact that a well-developed squama covers the halteres; others come quite as close to the Tachinidae, Muscidae and Sarcophagidae, but may readily be separated by the simple, not angulate, main vein of the wing. The larval habits are varied. Many attack vegetables, produce disintegration in them, thus facilitating decomposition. Anthomyia brassicae is renowned amongst market gardeners on account of its destructive habits. A. cana, on the contrary, is beneficial by destroying the migratory Locust Schistocerca peregrina; and in North America, A. angustifrons performs a similar office with Caloptenus spretus. One or two species have been found living in birds; in one case on the head of a species of Spermophila, in another case on a tumour of the wing of a Woodpecker. Hylemyia strigosa, a dung-frequenting species, has the peculiar habit of producing living larvae, one at a time; these larvae are so large that it would be supposed they are full grown, but this is not the case, they are really only in the first stage, an unusual amount of growth being accomplished in this stadium. Spilogaster angelicae, on the other hand, according to Portschinsky, lays a small number of very large eggs, and the resulting larvae pass from the first to the third stage of development, omitting the second stage that is usual in Eumyiid Muscidae.[[429]]
Fig. 242—Ugimyia sericariae. A, The perfect fly, × 3⁄2; B, tracheal chamber of a silkworm, with body of a larva of Ugimyia projecting; a, front part of the maggot; b, stigmatic orifice of the maggot; c, stigma of the silkworm. (After Sasaki.)
Fam. 35. Tachinidae.—First posterior cell of wing nearly or quite closed. Squamae large, covering the halteres: antennal arista bare: upper surface of body usually bristly. This is an enormous family of flies, the larvae of which live parasitically in other living Insects, Lepidopterous larvae being especially haunted. Many have been reared from the Insects in which they live, but beyond this little is known of the life-histories, and still less of the structure of the larvae of the Tachinidae, although these Insects are of the very first importance in the economy of Nature. The eggs are usually deposited by the parent-flies near or on the head of the victim; Riley supposed that the fly buzzes about the victim and deposits an egg with rapidity, but a circumstantial account given by Weeks[[430]] discloses a very different process: the fly he watched sat on a leaf quietly facing a caterpillar of Datana engaged in feeding at a distance of rather less than a quarter of an inch. "Seizing a moment when the head of the larva was likely to remain stationary, the fly stealthily and rapidly bent her abdomen downward and extended from the last segment what proved to be an ovipositor. This passed forward beneath her body and between the legs until it projected beyond and nearly on a level with the head of the fly and came in contact with the eye of the larva upon which an egg was deposited," making an addition to five already there. Ugimyia sericariae does great harm in Japan by attacking the silkworm, and in the case of this fly the eggs are believed to be introduced into the victim by being laid on mulberry leaves and swallowed with the food; several observers agree as to the eggs being laid on the leaves, but the fact that they are swallowed by the silkworm is not so certain. Sasaki has given an extremely interesting account of the development of this larva.[[431]] According to him, the young larva, after hatching in the alimentary canal, bores through it, and enters a nerve-ganglion, feeding there for about a week, after which the necessity for air becoming greater, as usual with larvae, the maggot leaves the nervous system and enters the tracheal system, boring into a tube near a stigmatic orifice of the silkworm, where it forms a chamber for itself by biting portions of the tissues and fastening them together with saliva. In this it completes its growth, feeding on the interior of the silkworm with its anterior part, and breathing through the stigmatic orifice of its host; after this it makes its exit and buries itself deeply in the ground, where it pupates. The work of rupturing the puparium by the use of the ptilinum is fully described by Sasaki, and also the fact that the fly mounts to the surface of the earth by the aid of this same peculiar air-bladder, which is alternately contracted and distended. Five, or more, of the Ugimyia-maggots may be found in one caterpillar, but only one of them reaches maturity, and emerges from the body. The Tachinid flies appear to waste a large proportion of their eggs by injudicious oviposition; but they make up for this by the wide circle of their victims, for a single species has been known to infest Insects of two or three different Orders.
Fig. 243—Diagrammatic section of silkworm to show the habits of Ugimyia. a, Young larva; b, egg of Ugimyia in stomach of the silkworm; c, larva in a nerve-ganglion; d, larva entering a ganglion; e, larva embedded in tracheal chamber, as shown in Fig. 242, B. (After Sasaki.)