Cockroaches are accomplished hitchhikers. In fact, German cockroaches usually first get into buildings by riding in boxes, in furniture and in other items brought into the building. Most other cockroach species invade from the outside or from sewers or drains. Most cockroaches prefer to rest on wood rather than on metal and other surfaces. That’s why you’ll often find them living in wood cabinets or in cardboard boxes. German cockroach fecal material contains a pheromone that tells other cockroaches that the area is a good place to harbor. Large numbers of cockroaches may congregate in areas where fecal material has accumulated. These areas are called aggregation points. All dishes and food items should be removed from shelving before treating for cockroaches. Good sanitation helps put stress on a cockroach population by making them more susceptible to treatments and baits.