Many people wonder where those larger roaches come from. The sewer roaches or the darker ones as from scurry across the pavement at night or sometimes you find in your house in the bathroom, near the garage. Every house in the city's connected by a storm drain. The cockroaches will come out through the manholes that are often times 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.