Safer"s BTK Caterpillar Killer is a biological insecticide that controls caterpillars including cabbage worm, tomato hornworm, tent caterpillars, gypsy moth, leafrollers, and other listed insects. Treat caterpillars when they first appear and are actively feeding for best results. Safer’s BTK™ Caterpillar Killer is most effective when caterpillars are small and young. This product is not effective on adult moths. Safer’s BTK™ Caterpillar Killer is a stomach poison and therefore must be ingested by the caterpillar to be effective. After ingestion of a sufficient product dose, feeding stops immediately and death will follow in 2-5 days.