Cockroaches are insects, of which about 30 species out of 4,500 total are associated with human habitations. About four species are well known as pests.
Among the best-known pest species are the American cockroach, which is about 1.2 in long, the German cockroach, about 0.59 in long, the Asian cockroach, also about 0.59 in in length, and the Oriental cockroach, about 1 inch. Tropical cockroaches are often much bigger.
Cockroaches have a broad, flattened body and a relatively small head. They are generalized insects, with few special adaptations, and may be among the most primitive living insects. The mouthparts are on the underside of the head and include generalized chewing mandibles. They have large compound eyes, and long, flexible antennae.
The first pair of wings are tough and protective, lying as a shield on top of the hind wings. All four wings have branching longitudinal veins, and multiple cross-veins. The legs are sturdy, with five claws each. The abdomen has ten segments.
Eggs and egg capsules
Female cockroaches are sometimes seen carrying egg cases on the end of their abdomen; the egg case of the German cockroach holds about 30 to 40 long, thin eggs, packed in a case called an ootheca. The egg capsule may take more than five hours to lay and is initially bright white in color. The eggs are hatched from the combined pressure of the hatchlings gulping air. The hatchlings are initially bright white nymphs and continue inflating themselves with air, becoming harder and darker within about four hours. Their transient white stage while hatching and later while molting has led many to claim the mis-conceived albino cockroaches.
A female German cockroach carries an egg capsule containing around 40 eggs. She drops the capsule prior to hatching, though live births do occur in rare instances. Development from eggs to adults takes 3 to 4 months. Cockroaches live up to a year. The female may produce up to eight egg cases in a lifetime; in favorable conditions, she can produce 300 to 400 offspring. Other species of cockroach, however, can produce an extremely high number of eggs in a lifetime. In some cases a female needs to be impregnated only once to be able to lay eggs for the rest of her life.
Cockroaches are among the hardiest insects on the planet. Some species are capable of remaining active for a month without food and are able to survive on limited resources like the glue from the back of postage stamps. Some can go without air for 45 minutes.
It is popularly suggested that cockroaches will "inherit the earth" if humanity destroys itself in a nuclear war. Cockroaches do indeed have a much higher radiation resistance with the lethal dose perhaps 6 to 15 times that for humans. However, they are not exceptionally radiation-resistant compared to other insects, such as the fruit fly.
Cockroaches are one of the most commonly noted household pest insects. They feed on human and pet food, and can leave an offensive odor. 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. These allergens have also been found to be linked with asthma.
General preventive measures against household pests include keeping all food stored away in sealed containers, using garbage cans with a tight lid, frequent cleaning in the kitchen, and regular vacuuming. Any water leaks, such as dripping faucets, should also be repaired. It is also helpful to seal off any entry points, such as holes around baseboards, in between kitchen cabinets, pipes, doors, and windows with some steel wool, copper mesh, cement, putty or silicone caulk.
Diatomaceous earth applied as a fine powder works very well to eliminate cockroaches as long as it remains in place and dry. Diatomaceous earth is harmless to humans and feels like talcum powder. Most insects, including bed bugs, are vulnerable to it.
Some cockroaches have been known to live up to three months without food and a month without water. Frequently living outdoors, although preferring warm climates and considered cold intolerant, they are resilient enough to survive occasional freezing temperatures. This makes them difficult to eradicate once they have infested an area.
There are numerous parasites and predators of cockroaches, but few of them have proven to be highly effective for biological control of pest species. Wasps are perhaps the most effective insect predators, as they attack the egg cases, and are predators on adult and nymphal cockroaches. The house centipede is probably the most effective control agent of cockroaches, though many homeowners find the centipedes themselves objectionable.
Bait stations, gels containing hydramethylnon or fipronil, as well as boric acid powder, are toxic to cockroaches. Baits with egg killers are also quite effective at reducing the cockroach population. Additionally, pest control products containing deltamethrin or pyrethrin are very effective.