They can be found in homes and domestic areas as well as commercial food premises, especially in blocks of flats, where they may live in kitchen ductwork and the drainage system.
The two main species from the public health point of view are the Oriental cockroach and the German cockroach. The adult Oriental cockroach may be 24mm long and almost black in colour; only the males have wings. The German cockroach is smaller, 14mm long, and is yellow brown in colour; both the males and females are winged.
Cockroaches are nocturnal insects; spending the day in cracks and crevices where they are difficult to detect. When you start to see evidence of an infestation, it is usually well established and professional help is needed. When cockroaches run over food they leave filth and spread disease. They secrete an oily liquid that has an offensive and sickening odour that ruins food. This odour may also be imparted to dishes that are apparently clean. Excrement in the form of pellets or an ink-like liquid also contributes to this nauseating odour. Some people are allergic to cockroaches and become ill. Cockroaches can contaminate food with certain bacterial diseases that result in food poisoning, dysentery or diarrhoea. They can also cause childhood asthma.
As with all the cockroach species, a combination of cockroach traps, gels and residual insecticides is the main approach. The effectiveness of the various residual insecticide formulations may be enhanced by using them in conjunction with insecticides applied as ULVs, mists, fogs or aerosols.