The German cockroach is very successful at establishing an ecological niche in buildings, and is resilient in the face of many pest control measures. Reasons include:
- lack of natural predators in a human habitat
- prolific reproduction
- short reproductive cycle
- the ability to hide in very small refuges
- sexual maturity attained within several weeks
German cockroaches are thigmotactic, meaning that they prefer confined spaces, and they are small compared to other pest species, so they can hide within small cracks and crevices that are easy to overlook, thereby evading humans and their eradication efforts. Conversely, the seasoned pest controller is alert for cracks and crevices where it is likely to be profitable to place baits or spray surfaces.
To be effective control measures must be comprehensive, sustained and systematic; survival of just a few eggs is quite enough to regenerate a nearly exterminated pest population within a few generations, and re-colonization from surrounding populations often is very rapid too.
Another problem in controlling German cockroaches is the nature of their population behavior. Though they are not social and practice no organized maternal care, females carry oothecal of 18-50 eggs (average about 32) during incubation until just before hatching, instead of dropping them as most other species of cockroaches do. This protects the eggs from certain classes of predation. Then, after hatching, nymphs largely survive by
consuming excretions and molts from adults, thereby establishing their own internal microbial populations and avoiding contact with most insecticidal surface treatments and baits. One effective control is insect growth regulators, which act by preventing molting and thus prevent maturation of the various instars. Caulking baseboards & around pipes may prevent the travel of adults from one room to another within a building.