Bt (Bacillus thuringiensis) is a naturally-occurring microorganism (soil bacterium) that produces proteins that kills any grub or insect that ingests it by paralyzing the bug’s digestive system. Bt is nontoxic to people, pets and the environment. It also doesn’t kill beneficial insects or their natural enemies (predators and parasites), or beneficial pollinators like butterflies or honeybees.
Institute of Cell and Molecular Biology, The University of Edinburgh
Bt is usually found in garden supply stores as a liquid Bt spray Bt does not last long so in many instances it must be reapplied. It can take up to 3 days to kill an insect after it has ingested it but in the meantime they stop feeding on your precious plants, roots and turf. It does not harm earthworms.