Worldwide some naturally occurring vertebrate pesticides, such as cyanide and strychnine, have been used for hundreds, possibly thousands of years to kill unwanted mammalian pests, and zinc phosphide has been used as a rodenticide for nearly 100 years. The most prolific period of research and development occurred between 1940 and 1990. Sodium fluoroacetate (1080) was developed in the 1940’s, first-generation anticoagulant rodenticides in the 1940s, 50s and 60s, and cholecalciferol and second generation anticoagulant rodenticides in the 1970’s and 80’s, partly to overcome resistance.