The Insect World. Figuier Louis

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СКАЧАТЬ a triangular piece, which the fly gets rid of when it is in a fit state to come into the open air."

      Fig. 47, taken from drawings in Réaumur's Memoirs, represents the imago of the Œstrus leaving the cocoon.

Fig. 47. Imago of Bot-fly emerging.		Fig. 48. Ovipositor of the Bot-fly (Œstrus bovis).

      The reader is, most likely, desirous to know with the aid of what instrument the Œstrus is able to pierce the thick skin of the ox.

      The female only is possessed of this instrument, which is situated in the posterior extremity of the body. It is of a shiny blackish brown colour, and as it were covered with scales. By pressing the abdomen of the fly between one's two fingers it is thrust out. Réaumur observed that it was formed of four tubes, which could be drawn the one into the other, like the tubes of a telescope (Fig. 48). The last of these appears to terminate in five small scaly knobs, which are not placed on the same line, but are the ends of five different parts. Three of these knobs are furnished with points, which form an instrument well fitted to operate upon a hard thick skin. United together, they form a cavity similar to that of an auger, and terminating in the form of a spoon.

      

      The Gad-fly, or Breeze-fly of the sheep, Œstrus (Cephalemyia ovis), has obtained notoriety on account of its attacking those animals.

      Even at the sight of this insect the sheep feels the greatest terror. As soon as one of them appears, the flock becomes disturbed, the sheep that is attacked shakes its head when it feels the fly on its nostril, and at the same time strikes the ground violently with its fore-feet; it then commences to run here and there, holding its nose near the ground, smelling the grass, and looking about anxiously to see if it is still pursued.

Fig. 49.—Cephalemyia ovis.

      It is to avoid the attacks of the Cephalemyia that during the hot days of summer sheep lie down with their nostrils buried in dusty ruts, or stand up with their heads lowered between their fore-legs, and their noses nearly in contact with the ground. When these poor beasts are in the open country, they are observed assembled with their nostrils against each other and very near the ground, so that those which occupy the outside are alone exposed (Plate III.). The Cephalemyia ovis (Fig. 49) has a less hairy head, but larger in proportion to the size of its body than the Gad-fly (Gasterophilus equi). Its face is reddish; its forehead brown with purple bars; its eyes of a dark and changing green; its antennæ black, its thorax sometimes grey, sometimes brown, bristling with small black tubercles; the abdomen white, spotted with brown or black; and the wings hyaline.

III.—Sheep attacked by Cephalemyia ovis.

      

      The Cephalemyia (Œstrus) ovis is to be found in Europe, Arabia, Persia, and in the East Indies. It lays its eggs on the edges of the animal's nostrils, and the larva lives in the frontal and maxillary sinuses. It is a whitish worm, having a black transverse band on each of its segments. Its head is armed with two horny black hooks, parallel, and capable of being moved up and down and laterally. Underneath, each segment of the body has several rows of tubercles of nearly spherical form, surmounted by small bristles having reddish points, and all of them bent backwards. "These points," says M. Joly, "probably serve to facilitate the progress of the animal on the smooth and slippery surfaces of the mucous membranes to which it fixes itself to feed, and perhaps also to increase the secretion of these membranes by the irritation occasioned by the bristles with which they are furnished." [16]

Fig. 50.—Conops.

      Fixed by means of these hooks to the mucous membrane, which it perforates, the larva nourishes itself with mucus, and lives in this state, according to M. Joly, during nearly a whole year. At the end of this time it comes out, following the same course by which it entered, falls to the ground, and burying itself to the depth of a few inches, is transformed into a pupa. The cocoon is of a fine black colour. Thirty or forty days after its burial it emerges in the perfect state, and detaching the lid at the anterior end of the cocoon by the aid of its head, which has increased considerably in size, takes flight.

      Notwithstanding the formidable appearance of their trunks, the habits of the perfect Conopes (Fig. 50) are very quiet. In the adult state they are only to be seen on flowers, of which they suck the honeyed juice. But with their larvæ the case is otherwise. These latter live as parasites on the humble-bees (Bombi). Latreille saw the Conops rufipes issue in the perfect state from the body of a humble-bee, through the intervals of the segments of the abdomen.

      

      The Mucides form that great tribe of Diptera commonly known as flies, and which are distributed in such abundance over the whole world. Faithful companions of plants, the flies follow them to the utmost limits of vegetation. At the same time they are called upon by Nature to hasten the dissolution of dead bodies. They place their eggs in the carcases of animals, and the larvæ prey upon the corrupt flesh, thus quickly ridding the earth of those fatal causes of infection to its inhabitants. The organs of these insects are also infinitely modified, in order to adapt them to their various functions.

Fig. 51.—Echinomyia grossa.

      M. Macquart divides the Muscides into three sections—the Creophili, the Anthomyzides, and the Acalyptera.

      The Creophili have the strongest organisation; their movements and their flight are rapid. The greater part feed on the juices of flowers, some on the blood or the humours of animals. Some deposit their eggs on different kinds of insects, others on bodies in a state of decomposition, some again are viviparous. The insects of the genus Echinomyia, for instance (Fig. 51), derive their nourishment from flowers. They deposit their eggs on caterpillars, and the young larvæ on hatching penetrate their bodies and feed on their viscera. How surprised, sometimes, is the naturalist, who, after carefully preserving a chrysalis, and awaiting day by day the appearance of the beautiful butterfly of which it is the coarse and mysterious envelope, sees a cloud of flies emerge in place of it!

      But there is another singular manœuvre performed by some of the species of the Diptera with which we are at present occupied to prepare an abundant supply of provision for their larvæ as soon as they are hatched. The following are the means they employ. It is well known that certain fossorial Hymenoptera carry their prey—other insects which they have caught, weevils, flies, &c., and which they intend should СКАЧАТЬ