There are about 3,500 species of cockroaches in the world, most of which are found in the tropics.

The common cockroach found in human dwellings contaminates food and is a great nuisance. The American or German cockroach are also pests in kitchens, bakeries and warehouses. There were only 2 species originally found in Britain but due to import of food and migration, several other species have been introduced there.

The domesticated species of cockroaches are omnivorous and can eat any sort of food. They are particularly fond of sweet and starchy food. In the absence of food, they feed on clothing, paper, books and even shoes. Thus they are severe pests in most households.

The cockroach is a nocturnal insect. It hides in dark cupboards and drawers and comes out only when it is dark. That is why if we happen to switch on the light in a dark kitchen at night, we can see them scurrying away into dark corners.
The cockroach has a flat body and is able to squeeze into the narrowest gaps and crevices. It has two long antennae for feeling and smelling its way in the dark. Its large eyes are not of much use. It has two pairs of wings which are used very rarely for flying.
The female cockroach lays the eggs in a horny, purse like egg case. She carries it around for some time beneath her abdomen till she deposits it by sticking it on a surface. The egg case contains about 16 eggs in 2 rows. The 'nymphs' that hatch out of these eggs are identical to the adult cockroach except that they are wingless, smaller and pale in colour. As they feed and grow older they become darker. They cast off their skin six or seven times during their growth period. This ceases when their development is complete. This process is known as incomplete metamorphosis. The butterfly, on the other hand, has a complete metamorphosis.

Man has invented several sprays and poisons for killing cockroaches but he has never been able to eradicate .them fully. They continue to come out from nooks and corners. They devour and contaminate our food and crawl all over our homes spreading diseases.