Rattlesnakes can grow from 0.5 to 2.5 meters in length, depending on the species. They all have a skin pattern, but their color can vary. All rattlesnakes have a triangular head and eyes with a black slit. Rattlesnake venom is poisonous to humans, but they are not trying to hurt us. They prefer to be left alone. They usually only strike when they are scared or startled.