Actually, Black Racers (Coluber constrictor) are very beneficial snakes. They will eat other snakes, small rodents, lizards, frogs and toads, and other animals. BTW--the term "poisonous" should not be applied to North American snakes--they are venomous, not poisonous, because they inject venom. Certain toads and frogs secrete poisons through their skin or through large glands on the sides of their heads. A toad can be poisonous to a dog. In Central America, the secretions from Poison-Arrow (or Poison-Dart) frogs are used to tip arrows used for combat.