Cockroaches are very uniform across species. The main difference is their size. They vary from a few millimetres in length to 70 millimetres. Of the 4000 species of cockroach in the world, 400 are present in Australia. The common house cockroach was introduced with white settlement.
Part of their resilience is attributable to the fact that they can eat almost anything - though their precise eating habits are largely unknown. They have a gut protozoa that aids in digestion of rotting wood, meaning that they are at home in older homes with a lot of wood in the building structure.
They can adapt to both wet and dry environments. Many species are nocturnal and will burrow in bark or burrows, live under logs or rocks, or in crevices during the day. Human habitation seems to attract them.