Because cockroaches contaminate food with their excrement and secrete an unpleasant odor which can permeate the indoor environment, these insects are considered by most homeowners and entomologists to be one of the worst household pests. Many individuals develop allergies to these insects. Allergens present in the feces of the German cockroach can become airborne along with normal house dust. The allergens can then be inhaled from the air or ingested when in contact with food. Cockroaches evolved as scavengers of decaying plant materials, hence they will readily feed on carbohydrates, but they will also feed on a variety of other foods, including paints, wallpaper pastes, and book bindings.
Homes also provide shelter and a multitude of warm and humid niches for their survival.
Interestingly, some evidence suggests that cockroaches adapted to life with primates because of the discovery of these insects in an orangutan nest. The lifecycle begins when a mature female cockroach produces an eggcase or ootheca. This habit can lead to the rapid dissemination of these insects, because each ootheca may contain hundreds of eggs which hatch into small versions of the adults, called nymphs. Nymphs can be recognized by the absence of wings, so conspicuously apparent in the adults. Mature cockroach nymphs are almost as large as the adults, but require another molt to reach adulthood.