(Length: 1/20″ – 1/8″) Chinch bug adults are grey-black insects with short white wings. They suck juices from plants such as grass and corn. In St. Augustine grass, their damage appears as a spot or brown patch with a dead or dying center and a yellowish margin. The spots grow bigger as the chinch bugs feed outwardly on the healthy grass. Hidden in the grass sheath, chinch bugs are often difficult to find.