Among all insects, the most common is the cockroach. The fossils found are evidence that cockroaches have existed for more than 300 million years. They are considered as one of the most successful groups of animals. Because cockroaches adapt easily to the environment, they have successfully adjusted to live with humans. There are about 3,500 species of cockroaches around the world and out of these, 55 species are found in the United States. Only four species are common pests in Pennsylvania structures. These are the German, Brown, Oriental and American Banded cockroaches. A fifth species, the Pennsylvania wood cockroach, is, on occasions, an annoying pest in certain places.