Many people wonder where those larger roaches come from. The sewer roaches or the darker ones that sort of scurry across the pavement at night or sometimes you find in your house in the bathroom or your garage. Every house in the city is connected by a storm drain. The cockroaches will come out through the manholes that are oftentimes located in your yard. When the climate changes and gets too wet or dries out too much these organisms, specifically the sewer roaches or oriental cockroaches, will come out these manhole covers and look for more stable environment. Frequently that's your yard, they infest vegetation there eating decaying organic matter and eventually migrate into the house putting pressure inside on the home.