This illustration shews why House Flies are one of the nastiest and most dangerous of pests. When feeding on meat, bread, or sugar they eject a liquid to dissolve the food before sucking it up.
The common House Fly (Musca Domestica) is barely a quarter of an inch tall, and measures from nose to tail less than three-eighths of an inch: its compact form is a model for Nature's most effective germ-dispensing mechanism.
Attached to its hairy body and stick-padded feet are germs of the widest range of diseases, including Amoebic dysentery, Bubonic plague, Gangrene, Leprosy, Tuberculosis, and Typhoid fever. The average number of germs found on a Fly's body is around 1,250,000 and can reach as high as 6,600,000.
The Fly is not affected by any of the germs it carries, it seems immune to them all.
During every 60 seconds a House Fly is in the air, its wings beat almost 20,000 times. In each wing-beat the Fly moves its two veined and transparent supporting surfaces in an intricate evolution - the tips move through the air in a series of figure eights, an entirely different form of wing-beat from a bird which remains aloft with fluttering or rowing motions. About eleven per cent of a Housefly's body is composed of the powerful motor muscles that operate its wings allowing it to travel at about 5 miles per hour.
One reasons a Fly, whether on the wing or at rest, is so hard to hit is the nature of its eyes. Humans have two lenses - one in each eye, the Housefly has eight thousand lenses - four thousand in each eye. Bulging outward from the sides of its head, the thousands of six-sided lenses fit together like honeycomb cells, and provide wide-angle vision unknown to humans; because the Fly has no eyelids it sleeps with its eyes open.
The House Fly has four life stages - egg, larva, pupa, and adult. the larvae crawl away from light, whereas the the adult House Fly is attracted to it, the male Housefly is more strongly attracted than the female. However, the females who use their sense of smell to find the best places for laying eggs, have a keener response to odors. Their smelling equipment is not a nose - it is a pair of stick-like feelers thrust out from between the eyes. Olfactory pits on these feelers enable the Houselies to catch faint odors not noticeable to the human nose.
Descending from the bottom of a House Fly's face is a proboscis, or sucking tube, ending in soft, fleshy mouthparts, this is its feeding equipment. It cannot bite because it has nothing with which to bite. It possesses no piercing beak or cewing jaws, it consumes only liquids. If a "Housefly" bites you , it isn't a Housefly, it is probably a Stable Fly that has come into the premises; these pests often come indoors before a rain shower, giving rise to an old belief about House Flies biting before a storm.
The fact that House Flies are on a permanent liquid diet increases their menace. When a Housefly lands on a food or other matter, it has to transform the solids into liquids. To do this it regurgitates some of the liquids already swallowed, together with its germ-laden saliva and waits until the surface is softened and liquified, it then reswallows the liquid leaving behind innumerable microbes.
The pads on a House Fly's feet consist of many short hairs exuding an adhesive substance to keep it from falling when it lands on a wall or ceiling. These pads are highly effective germ traps. Whenever a House Fly pulls away from a microbe-laden surface innumerable minute organisms come with it. Later, when the feet are set down again, the bacteria are deposited and left behind.
Let a House Fly walk across a dish of unsweetened gelatin and set it away for a couple of days and you will find the trail of its wandering shewing up as a whitish mold. The bacteria left behind have multiplied on the gelatin and are now visible to the naked eye.
Throughout its life the House Fly is associated with bacteria and filth, the eggs of the female, about 600 in all, are laid in batches of from 100 to 120. Sunshine stimulates breeding activity, and eggs develop with amazing rapidity. Often only 8 hours elapse before they hatch into larvae, wedge shaped, almost transparent, legless, and virtually headless. These larvae feed on the products of decay, shed their skins several times, and reach full size - about three eighths of an inch - in five or six days. During this time the maggot seeks the warmest spot it can find.
When feeding days are over, the larva retreats to a cooler place, its skin hardens , turns red , its body contracts, it becomes a pupa. Within this pupa the tissues are being re-formed into an intricate, winged and legged body; this transformation takes four or five days. After getting its wings the skin is shed and the adult Housefly emerges and grows no more. The smaller Flies sometimes seen are not "Little House Flies" - they are usually adults of another species, (Fannia Canicularis).
The complete lifecycle of the House Fly, from egg to emergence of the adult, lasts only a couple of weeks. As many as fourteen generations may follow each other in the course of a single summer.
Throughout its life the House Fly is associated with bacteria and filth, and effective Housefly control includes good sanitation and cleanliness. This is especially true in food preparation and serving areas.
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