For every cockroach you see, there are a hundred hidden. Not only do they contaminate food and utensils but readily spread disease causing organisms leading to dysentery, diarrhea, food poisoning and asthma. They also leave dark stains and foul odours leading to very unpleasant and unhygienic conditions. There are about 4.000 species of cockroach of which 30 species are associated with human habitations and about four species are well known as pests.