German cockroaches gather, or aggregate in dark places that have high humidity, contain paper, wood and other porous surfaces and have food readily available. A pheromone is a chemical produced by one cockroach that affects the behavior of others. This aggregation pheromone is very attractive to the immature stages. The end result is that German cockroaches congregate in areas near porous surfaces that have little air movement, are dark and have large quantities of their own feces. Examples of these gathering places are in cracks and crevices around cabinets, wall and ceiling voids, in and around refrigerators, dishwashers, stoves, washers and dryers, and water heaters.
German cockroaches thrive in undisturbed, protected habitats that contain food and water.
The most favorable humidity levels are found in kitchens and bathrooms under and around toilets, bathtubs, showers and sinks. They especially like sink traps, leaking faucets, standing water and wet sponges. German cockroaches will not leave these favorable areas unless they are forced out. When any of these resources are eliminated, populations can't grow and may even decline. More details on how to eliminate resources are in Chapter 5 .