Page:The American Cyclopædia (1879) Volume VII.djvu/302

 294 FLY killed by cold weather ; the eggs are deposited in dung, in which the fleshy larvae undergo their transformations; consequently this spe- cies is most numerous in the vicinity of stables and unclean places. The swarms of summer are doubtless the progeny of a few individuals House Fly (Musca domestica), magnified. which have survived the winter in some pro- tected nook, and are not produced from eggs laid the preceding season ; it is possible that a few may pass the winter in the pupa state, and be developed by the warmth of spring. Among the thousands of domestic flies, all are of the same size, those larger or smaller being of dif- ferent species, and neither very old nor very young individuals of the M. domestica. The house fly is such a constant companion of man, that its presence in a coral or other island is sufficient evidence that human inhabitants are not or have not been far distant. Its two compound eyes contain 4,000 facets, each the cornea of a separate ocellus; the spiracles through which air enters the tracheae are pro- vided with a kind of sieve formed by minute interlaced fibres, which prevent the introduc- tion of dust and foreign substances. The hard parts of the proboscis are undeveloped, in their place being a fleshy tongue-like organ, or la- bium, bent underneath the head when at rest. Its knob-like end may be extended into two flat, broad, fan-shaped muscular leaves, by whose sucker-like surface the fly laps up liquid sweets, as sugar dissolved by its own saliva. The leaves are supported on a framework of tracheae, which end in projecting hairs, acting as a rasp on delicate surfaces, and causing a tingling on the naked skin of man. It is well known that flies, like many other insects, have the power of creeping up smooth perpendicular surfaces, and of walking on ceilings with their backs downward. The last joint of the tarsus has two strong hooks, and a pair of membra- nous expansions (pulvilli), beset with numerous hairs, each having a minute disk at the ex- tremity. There has been considerable differ- ence of opinion as to the precise mode in which this apparatus enables the fly to walk in op- position to the force of gravity. Derham, Home, Kirby, and Spence believed that the pulvilli act as suckers, a vacuum being formed beneath, and that the insect is held up by the pressure of the atmosphere against their upper surface ; others have maintained that the ad- hesion is due to a viscid liquid secreted from the bottom of the foot. Dr. Hooke and Mr. Blackwall assert that the soles of the feet are so closely beset with minute bristles that they cannot be brought in contact with any surface so as to produce a vacuum, and believe that the support is owing to the strictly mechanical action of these hooks. Mr. Hepworth (" Jour- nal of Microscopical Science," vols. ii. and iii.) reconciles these apparently contradictory opin- ions by the conclusion that the minute disks at the end of the individual hairs act as suckers, each of them secreting a non- viscid liquid, which renders the adhesion perfect ; a structure which exists on a larger scale in the feet of dytiscus and other beetles. Mr. White, in his "Natural History 'of Selborne," observes, in confirmation of the views of Derham, that to- ward the close of the year, when flies crowd the windows in a sluggish and torpid condi- tion, they are hardly able to lift their legs, and many are actually glued to the glass, and there die from inability to overcome the pres- sure of the atmosphere. It is well known that some lizards possess a similar faculty, and a similar apparatus to account for it. A dish of strong green tea, well sweetened, will be eagerly tasted by flies, and prove a cer- tain poison ; according to Mr. Spence, a netting of large meshes stretched across a window of a room lighted only on one side will not be passed by flies. The blue-bottle or blow fly (M. [calliphora] vomitoria. Linn.) is a large, buzzing species, blue-black, with a broad, steel-blue, hairy hind body; it is found in summer about slaughter houses and all places where meats are kept, which it frequents for the purpose of depositing its eggs on animal substances. The eggs, usually called fly blows, are hatched in two or three hours ; the lar - Blue-Bottle (Musca vomitoria). increase SO rapid- Larva and Pupa. ty m three or lour days, and are so vo- racious, that Linnaeus did not greatly exagge- rate when he said that the larvae of three fe- males of this species will devour the carcass of a horse as quickly as would a lion ; they pass the pupa state in the ground or in some crevice, the larval skin not being cast off, but changed into an egg-shaped case; from this they emerge as flies in a few days, or, if hatched late in the season, remain unchanged through the winter. A smaller, brilliant, blue-green fly, with black legs, much resembling the M. (lucilia) Ccesar of Europe, lays its eggs on meat and the carcasses of animals. The flesh fly (sarcophaga carnaria, Meig.), somewhat