Cockroaches have a broad, flattened body and a relatively small head. They are generalized insects, with few special adaptations, and may be the most primitive living insects. The mouthparts are on the underside of the head and include generalized chewing mandibles. They have large compound eyes, two ocelli, and long, flexible, antennae.
Cockroaches live in a wide range of environments around the world. Pest species of cockroaches adapt readily to a variety of environments, but prefer warm conditions found within buildings. They generally live in moist areas, but can survive in dry areas if they have access to water. They are scavengers that feed on decaying organic matter and a variety of other foods, particularly fermenting foods. Cockroaches are common in kitchens, bathrooms, basements, crawl spaces, cracks and crevices of porches, foundations, and walkways adjacent to buildings.
Cockroaches leave chemical trails in their feces as well as emitting airborne pheromones for swarming and mating. Other cockroaches will follow these trails to discover sources of food and water, and also discover where other cockroaches are hiding.
Cockroaches can live up to a year. The female may produce up to eight egg cases in a lifetime; in favorable conditions, it can produce 300 to 400 offspring. Other species of cockroach, however, can produce an extremely high number of eggs in a lifetime, but in some cases a female needs to be impregnated only once to be able to lay eggs for the rest of her life.
A female German cockroach carries an egg capsule containing around 40 eggs. She drops the capsule prior to hatching, though live births do rarely occur. Development from eggs to adults takes 3 to 4 months.
They can also passively transport microbes on their body surfaces including those that are potentially dangerous to humans, particularly in environments such as hospitals. Cockroaches have been shown to be linked with allergic reactions in humans.