Flies can find their way into practically any living space, their ability to infect surfaces with bacteria resulting in serious disease and food poisoning coupled with the relative frequency of encounters with this pest means that serious action must be taken to eliminate this pest from your commercial or residential property.
Flies will often feed and lay eggs on rubbish, manure and dead animals before flying off to land on food preparation areas or object used orally, such as a glass. When feeding,  a house fly will regurgutate its stomach contents onto its food, to liquify it and make it easier for them to ingest. Surfaces and food may also be contaminated by the fly defating.

House Fly 

 

Signs of infestation: Groups of flies, alive or dead.Spots / droppings on surfaces or food. Maggots, which are flies in their larval stage.
 

Facts :The adults are 8–12 mm long, with a gray, hairy like body.. The females are slightly larger than the males, and have a much larger space between eyes.The house fly lives an average of 21 days, and its wings beats 200 times per second.
Flies are born full adult size. There 4000 lenses in each compound eye.
Flies jump up and backwards when taking off, making them difficult to swat.

Diseases : Flies can carry/cause Campylobacter, Streptococci
Salmonella, Chlamydia, Dysentery, Urinary Tract Infections, Gastroenteritis ,Lower Respiratory Infections

Other types of common fly include
Blowflies (Bluebottle, Greenbottle)lowflies (Bluebottle, Greenbottle) which have a shiny metalic body and 3 segmented antennae.
Fruitflies - Usually about 3 mm long and usually have red eyes.