Safer Brand 16 oz. Caterpillar Killer II Concentrate kills worms and caterpillar stage insects but has no effect on birds, earthworms, or beneficial insects when used as directed. The caterpillars and worms that are damaging your plants will stop feeding immediately after ingesting the bacterium, which is known scientifically as Bacillus Thuringiensis var. Kurstaki (B.t. for short).Use in late afternoon or on cloudy days since the BT breaks down in sunlight. Controls tent caterpillars, gypsy moths, cabbage loopers, tomato horn worms and more. Safer Brand Caterpillar Killer is OMRI Listed and can be used up until the day of harvest.