American Cockroach Diet-Utilitarian
To get an idea of the utilitarian nature of an American cockroach's diet, consider that it has been observed eating the following items: paper, boots, hair, bread, fruit, fish, peanuts, old rice, putrid Japanese sake, the soft part on the inside of animal hides, cloth and dead insects. In other words, if something can be chewed and digested for protein value, chances are a cockroach has at one point or another eaten it.
German Cockroach Diet-Slightly More Discriminating
German cockroaches have a a slightly higher fondness for water and moisture than their American species counterpart. They can live up to a month on water alone, but without food or water, they are likely to die within two weeks. The breadth of what a cockroach will eat is truly astounding. For example, these insects have been known to consume the glue off the back of a postage stamp and the glue that seals book bindings, because these types of adhesives are generally made from some sort of animal protein.
Roaches of the Sea
In terms of the overall food chain, the role performed by cockroaches on firm ground is similar to the one carried out in the water by lobsters, who are sometimes referred to as "roaches of the sea." In both cases, their role is to clean up dead and dying plants and animals from their environment. As so-called omnivorous scavengers, cockroaches now apply this behavior to apartment and household kitchens, "cleaning" whatever has been dropped or left behind.