Safety
In general, Bt is very safe for use. The U.S. Environmental Protection has found no hazards to human health associated with the use of Bt. The EPA considers Bt sufficiently safe that it has exempted it from food residue tolerances, groundwater restrictions, endangered species labeling and special review requirements. Bt has no known effect on nontarget organisms in aquatic and terrestrial habitats, including bees, fish, birds, and wildlife. It is the pesticide of choice for use near lakes, rivers, and dwellings.
In some instances, killing of nontarget caterpillars could be of concern, especially if they are rare or beneficial species that are in the caterpillar stage at the same time and location as the target species.