Norway rats, also known as brown or sewer rats, can grow up to 13 - 16 inches long. They are not native to Las Vegas and have probably arrived on building materials shipped in from out of state.
These rodents multiply quickly, living in polygamous colonies and mating year round in some areas. Female roof rats can reproduce at three to five months old giving birth to a litter. They can mate again after approximately 18 hours of giving birth. Roof rats feed on vegetation, eating fruits, grains, seeds, and whatever you just brought home from the Farmer's Market. Norway rats eat just about everything.