This is the harmless hognose snake, which is sometimes called the "puff adder" or "spreading adder". Hognose snakes in Florida range from brown and tan spotted or barred to grey and black or entirely black. These unusual snakes rarely bite in self defense, though they may spread a "hood", hiss loudly or even turn over and play dead if you frighten them.

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Quick guide    Animal Diversity Web     Unversity of Florida    Hognose.com