The German cockroach is very successful at building an ecological niche in structures and is durable in the face of many pest-control treatments. To be effective, control solutions must be thorough, continual, and methodical; survival of merely a few eggs is quite enough to reproduce a virtually exterminated pest population within a couple of generations, and recolonization from surrounding populations often is very rapid, too.
German cockroaches like cramped areas, and they are small compared to other pest species, so they can hide within small gaps and crevices that are easy to discount, therefore evading human beings and their removal efforts.
A type of German cockroaches has emerged that reacts to glucose as distastefully bitter. They refuse to eat sweetened baits, which presents a challenge to their control, considered that those baits are an economical and effective way of regulation.