Houseflies can take in only liquid foods. They spit out saliva on solid foods to pre-digest it, and then suck it back in. They also vomit partially digested matter and eat it again.
The flies can walk on vertical planes, and can even hang upside down from ceilings. This is accomplished with the surface tension of liquids secreted by glands near their feet.
Flies continually preen themselves, cleaning their eyes with their forelegs and dusting off their legs by rubbing them together. They do this because most of their taste and smell receptors are on the hairs of their legs.
Flies have a very highly-evolved evasion reaction which helps to ensure their survival. It is possible to confuse a fly’s evasion system by swatting it with two objects simultaneously from different directions. The holes in a fly swatter minimize the air current which warns the fly of being hit, whilst reducing air resistance and increasing speed of the swat. This evasion reaction can also be used against the fly. Clapping your hands several inches above the fly will cause it to try to escape, usually into your just closing hands. A successful method of removing flies from living spaces is to use a vacuum cleaner equipped with a long (1m/3 feet)straight tube at the end of a flexible hose. Airborne flies can be chased with the tube and will eventually be sucked into it. Standing flies can be approached slowly with the tube (1cm/half-an-inch per second) and often they will not fly away and will be sucked into it.
Even though the order of flies (Diptera) is much older, true houseflies evolved in the beginning of the Cenozoic era, some 65 million years ago. They are thought to have originated in the southern Palearctic region, particularly the Middle East. Because of their close, commensal relationship with man, they probably owe their worldwide dispersal to co-migration with humans.
Flies and Humans
In colder climates, houseflies occur only with humans. They have a tendency to aggregate and are difficult to dispel. They are capable of carrying over 100 pathogens, such as typhoid, cholera, Salmonella, bacillary dysentery, tuberculosis, anthrax, ophthalmia, and parasitic worms. The flies in poorer and lower-hygiene areas usually carry more pathogens. Some strains have become immune to common insecticides.