Natural Guard Caterpillar Killer (1 pint/16 oz concentrate) is a biological insecticide containing Bacillus thuringiensis (Bt) subsp. kurstaki, designed to kill leaf-chewing worms and caterpillars (e.g., tomato hornworms, loopers, bagworms) on vegetables, fruits, and ornamentals. It is non-toxic to humans, pets, and beneficial insects like bees.