“Does Iowa have any poisonous snakes?”
It’s a question that comes up when visitors see our animal ambassador snakes, and the answer is “No.”
That might not be what you expected.
You see, snakes in North American are not poisonous, they are venomous — which means they inject a toxin rather than secreting a poison from the skin. It’s rare for a snake to be both poisonous and venomous. Snakes in the genus Rhabdophis, found in Asia, are both venomous and poisonous.
Iowa does have four species of venomous snakes: Copperhead (Agkistrodon contortrix), prairie rattlesnake (Crotalus viridis), eastern massasauga (Sistrurus catenatus) and timber rattlesnake (Crotalus horridus).
Although there are no universal identifying features of venomous snakes, among Iowa’s venomous snakes, there are some identifying characteristics to watch out for.
A rattle on the end of the tail
Three of Iowa’s four native, venomous snakes have a rattle on the end of the tail. This is a tool the snake uses as a warning to those getting too close. However, a rattlesnake may not “hear” — through vibrations — humans approaching, so it may not rattle. That’s why people should always be aware in an area with rattlesnakes.
A rattle is composed of hollow, interlocked segments made of keratin, and the snake uses muscles to vibrate the segments against each other. This creates the tell-tale sound.
Sight varies greatly among snakes, with some only being able to discern fuzzy shapes and a few colors to others with clear, but not sharp, vision. The ones with clear vision can track movement but cannot tell a mouse from a vole.
During hot summer months, several Iowa snakes become nocturnal. Being active and hunting at night is far less energy expensive for the energy conservative snake. So, if so many are active at night, how do they hunt so effectively? Non-venomous snakes that switch to nocturnal activity rely on external light and their keen sense of smell to compensate for their not-so-sharp eyesight.
However, venomous snakes have evolved to “see” very well at night. The venomous snake species of Iowa have special heat-sensing pits that sense infrared radiation — the body heat of other animals. These pits are located on each side of the snake’s head, between the eye and the mouth.
All of the venomous snakes in Iowa have elliptical pupils, and many people think that applies to allow venomous snakes in the world. However, this isn’t a hard-and-fast rule. Some highly aggressive snakes in the world have round pupils.
Venomous snakes have fangs that are sharp, enlarged teeth along the upper jaw. They can be at the front or the back of the snake’s mouth, and they are connected to venom glands. Even non-venomous snakes have teeth.
Many of these signs of venomous Iowa snakes are only noticeable up close, so it is always best to be aware of where you are walking and what wildlife might be in that area. Whether a snake is venomous or not, if you’re unsure, just leave it alone. A great general rule for any wildlife is, enjoy the view, but let wild be wild.