Combat Source Kill Max large roach bait is formulated with food that specifically attracts American roaches and other large roaches, plus the powerful insecticide Fipronil, which starts killing within hours. Like all Combat products, these baits target the nest to eliminate the source of the problem, not just the few roaches you see. These easy-to-use, child-resistant baits need no activation. Simply place them down for up to three months of large roach control.