It is humbling and instructive that the most exquisitely specific group of insecticides known originates not from a laboratory, but instead from the common soil bacterium Bacillus thuringiensis (Bt).  Insecticidal crystal proteins produced by Bt kill insects by binding to and disrupting their midgut membranes.  each of the numerous strains of Bt produces a characteristic set of crystal proteins.  Each of these toxins is lethal to certain insects, yet does little or no harm to most other organisms, including people, wildlife, and even other insects.