Nature Bulletin No. 453-A   April 15, 1972
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

****:THE HOUSEFLY

We are bolder than we realize because, as the old saying goes: 
"Familiarity breeds contempt". People get goose pimples while 
watching some horror film on television, and shudder at pictures of 
spitting cobras, prowling panthers, or man-eating sharks and other deep 
sea monsters. Yet every summer and without a qualm, they face one of 
the most dangerous animals in the world -- the common Housefly.

It does not bite and it does not sting but every time it lights on us or on 
our food there is a chance that it will leave behind a germ of some 
human disease. It can transmit typhoid fever, diarrhea, dysentery, 
cholera, trachoma and perhaps, tuberculosis and polio. In fact, another 
name for it is the Typhoid Fly.

Since earliest times, throughout the world, the housefly has associated 
with man and been a pest to him. Fortunately, in America, it is now 
must less common and much less of a threat than in the horse and buggy 
days when it bred mostly in the manure piles around stables. 
Automobiles and trucks have replaced the horses. Garbage and filth, 
also prolific breeding places for houseflies, are largely disposed of in a 
sanitary manner. Nowadays we swat the fly, electrocute them, screen 
our homes, spray the garbage dumps and spray the barns on farms.

DDT and other insecticides developed during World War II were 
extensively used to control flies but after a few years, unfortunately, 
these insects develop strains which are immune. Consequently there is a 
constant search for new and more effective poisons. Some day, we 
hope, there may hardly be a safe place for a fly to light.

The housefly combines a capacity for producing great numbers of 
young with one of the shortest life cycles known. A few flies in early 
summer can produce millions of descendants by fall, and as many as ten 
generations in that single season. Each female lays about 500 slender 
whitish eggs in batches of a hundred or more at a time. A half-day later, 
in warm weather, each egg hatches into a tiny white larva called a 
maggot. After five days or more, the larva is full-grown and then 
transforms into a quarter-inch, brown, seed-like pupa or "resting stage". 
From these pupae, 3 or 4 days later, the adults emerge and are soon 
ready to start families of their own.

The average life span of an adult housefly is from 20 to 30 days. 
Occasionally, one may survive freezing weather if hidden away in a 
warm building but most of the parents of each year's crop spend the 
winter as maggots or pupae buried in stable litter or under piles of 
rotting grass.

Houseflies prefer bright sunlight but may be active in artificial light. 
Insatiable curiosity, guided by good eyesight and a keen sense of smell, 
leads them to explore every spot, stain, crumb or bit of spilled food. 
They have a thirst for and, having sucking mouthparts, can feed only on 
liquids. Solid foods such as grains of sugar, are sponged with saliva 
until dissolved and then swallowed.

A housefly's two transparent wings buzz at about 160 beats per second. 
Marked flies have been recaptured after traveling as much as 13 miles 
but, usually, they travel no farther than the nearest place to feed and lay 
eggs -- perhaps in the same city block. Each of a fly's six feet ends in a 
pair of claws and a pad covered with hairs that exude a sticky fluid. 
That is why they are able to walk up a polished window pane or stroll 
around on a ceiling. They like to roost on a warm spot with a good view 
all around and a favorite perch, when you take an afternoon nap, is on 
the end of your nose.