Here is some information that I have gathered, most of it is cut and paste from articles I have found The question on another thread was whether there were certain types of Bt that harmed good guy animals like butterflies and moths. Some commercially available Bt varieties and target pests: Bacillus thuringiensis var. tenebrionis - Colorado potato beetle and elm leaf beetle larvae var. kurstaki - caterpillars var. israelensis - mosquito, black fly, and fungus gnat larvae var. aizawai - wax moth larvae and various caterpillars, especially the diamondback moth caterpillar Mode of Action The toxic crystal Bt protein in commercial formulations is only effective when eaten by insects with a specific (usually alkaline) gut pH and the specific gut membrane structures required to bind the toxin. Not only must the insect have the correct physiology and be at a susceptible stage of development, but the bacterium must be eaten in sufficient quantity. When ingested by a susceptible insect, the protein toxin damages the gut lining, leading to gut paralysis. Affected insects stop feeding and die from the combined effects of starvation and tissue damage. Bt spores do not usually spread to other insects or cause disease outbreaks on their own as occurs with many pathogens. Bacillus thurengiensis isreali Bti, most often sold as a hard donut, fights mosquitoes when placed in standing water. And is a bacteria that is toxic to mosquito larvae. The bacteria causes the stomach lining of mosquito larvae to rupture and ultimately killing the mosquito larvae. Bt is used to kill caterpillars before they have a chance to pupate into winged adults, Bacillus thuringiensis kurstaki (B.t.k.) is a naturally occurring bacteria found in the soil. An inactive, or spore, form of the bacteria is approved by the Environmental Protection Agency (EPA) for use as a pesticide to control the gypsy moth. B.t.k is commonly used by organic gardeners and is approved for use on more than 200 food and grain crops in the U.S. Over 100 million pounds are used each year in the U.S. B.t.k. is harmful to moths and butterflies that are in their caterpillar stage. Caterpillars that eat B.t.k. on trees and shrubs die when the B.t.k. spores are activated in the insects' stomachs.