The adult German Cockroach is a light yellow/brown and is 10 to 15mm long. The Oriental Cockroach is dark brown/black and is 20 to 24mm long. Immature stages of Cockroach, look exactly like adults, just on a smaller scale.There are two main species of cockroach in Britain, Oriental and German Cockroaches
The fast way for the German cockroach to infest a building where are multiple flats is from common waste pipes, plumbing and electric cables connecting the flats. The cockroach follow the pipes and access the kitchen and recycle areas where the people dump the food waste. Then if one flat has a cockroach infestation in a short period of time others get infested.