German cockroaches Blattella germanica feeding on food scraps left on linoleum floor. This species is the number one cockroach pest in the world that most often infests homes, restaurants, and hotels. It is the smallest cockroach pest and adults averages just over a centimeter in length. Domestic cockroaches cause billions of dollars of damage every year just in the contamination of food products. What磗 worse, they can cause allergies and carry diseases like dysentery and typhoid.