Flies

 

 

 

 

 

 

 

 

 

 

 

 

In South Africa, the Housefly is represented by two main species, the Common House Fly (Musca domestica) and the lesser Housefly (Fania canicularis).  Common Houseflies are a worldwide pest of homes, shops, factories, catering establishments and rubbish tips.  They are ubiquitous insects with a flight range of at least 8 kilometres.  They are highly active indoors and in our warm climate they remain active and reproduce throughout the year.   The adult is attracted to and breeds in decaying animal and vegetable waste.  Common Houseflies are a major health risk as they are potential vectors of diseases such as dysentery, gastroenteritis, typhoid, cholera and tuberculosis.  They will frequent and feed indiscriminately on any liquifiable solid food, which may equally be moist, putrefying material or food stored for human consumption.  They liquify  food by regurgitating digestive juices and their stomach contents on to the food substance.  This ‘liquid’ is then drawn up by its mouth parts and in so doing they pick up pathogenic organisms which may collect on their bodies to be transferred on contact with other surfaces or survive passage through the gut to be deposited as fly spots.  Flies are frequently the subject of complaints to environmental health authorities, causing major problems where infestations overspill from breeding sites.  Lesser Houseflies are frequently encountered in poultry houses.  They make longer flights and spend less time resting than the Common Housefly.  Females of the species tend to remain near the breeding sites and only the males migrate.  They commonly occur indoors and they fly on irregular triangular or square courses in rooms usually under pendant lamps.

 

The life cycle of the Common Housefly starts when the newly emerged fly remains unable to fly for up to two hours while its wings stretch and harden.  The female is able to lay her first batch of eggs 2 - 9 days after emerging.  100-150 eggs are laid 4-5 times at intervals of several days.  Eggs hatch in 6 hours to 2 days depending on the temperature and moisture.  The larvae feed actively and in 3 - 5 days are fully grown and ready to pupate.   To pupate the larvae migrate to cooler and drier conditions and usually the soil around the breeding medium in which they pupate.  At this stage the larvae transform to the adult.  This may take 3 - 4 days.  The hard puparium shell is impervious to insecticides, but high temperature and desiccation are lethal.

 

It can be seen from the life cycle of the House fly that a full generation can take as little as 8 days in the Summer.  With as many as 10-20 generations a season, it is easy to see how sudden outbreaks of flies occur under favourable breeding conditions.