Venomous snakes of Iowa

"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).

Photos of Iowa's venomous snakes

Although there are no universal identifying features of venomous snakes, among Iowa's venomous snakes, there are some identifying characteristics to watch out for.

Graphic about venomous snake characteristics

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.

Heat-sensing pits

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.

(Read about how snakes smell.)

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.

Elliptical pupils

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.

Fangs

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.

(Watch how the nature center snake's eat on our Videos page.)

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.

(Watch our community relations coordinator attempt to hold a snake for the first time.)

How a snake breathes while it eats

Just because they work for a conservation board doesn’t mean that naturalists know everything. Just last week, naturalist Ashley Hansen was feeding Rosie the corn snake when she noticed a hole open up in the snake’s mouth while it was eating a mouse — the Dickinson County Nature Center snakes are fed mice that are Read More »

Read More

13 Comments

  1. Terri on January 29, 2020 at 11:52 pm

    I see from the comments there are a lotof people concerned about snakes.
    Clearly, I am not alone.
    Right now I live in western Washington where there are no venomous snakes. Don’t think we can afford to retire here. I’m scared to go anywhere with venomous snakes. 😉



  2. Michelle on September 22, 2019 at 4:43 pm

    What about water moccasins and cotton mouths



    • kiley on September 23, 2019 at 10:46 am

      Water moccasins, otherwise known as cottonmouths, are not typically found in Iowa. They are not considered an “Iowa snake.”



  3. Maryann Ressler on July 27, 2019 at 9:28 am

    I was told that there is no venomous
    s snakes in Iowa. Apparently that’s not true. Are there any venomous
    snakes in Cerro gordo county?



    • kiley on July 29, 2019 at 8:12 am

      These types of snakes are not very widespread in Iowa. The timber rattlesnake has been found in eastern and southern Iowa. The massasauga was found in a couple of state marshes. The prairie rattlesnake has been seen in the northern portions of the Loess Hills, rarely, and the copperhead can be seen in a small area in southeastern Iowa.



  4. Lisa Guadagnoli on May 9, 2019 at 12:49 am

    are they going to pursue a individual and attack?



    • kiley on May 9, 2019 at 8:03 am

      Definitely not — if you leave them alone, they will leave you alone. Wild animals just want you to leave them be.



  5. Thelma Morris on April 20, 2019 at 4:21 pm

    Can garter snakes become aggressive? I had one strike out at me today. The snake had yellow stripes down the length of it’s body. I think the body was green but my husband thought it was brownish.
    Thanks



    • kiley on April 22, 2019 at 8:07 am

      Most garter snakes are docile, but some may try to bite or lash out in self-defense. It may have felt threatened.



  6. Mr. Curious on September 26, 2018 at 6:37 pm

    Where in Iowa do these snakesive, are they in Dickinson County?



    • kiley on September 27, 2018 at 8:59 am

      These types of snakes are not very widespread in Iowa. The timber rattlesnake has been found in eastern and southern Iowa. The massasauga was found in a couple of state marshes. The prairie rattlesnake has been seen in the northern portions of the Loess Hills, rarely, and the copperhead can be seen in a small area in southeastern Iowa.



  7. Tim on September 26, 2018 at 11:15 am

    Great information! Are these snakes in every county of Iowa?



    • kiley on September 27, 2018 at 8:59 am

      These types of snakes are not very widespread in Iowa. The timber rattlesnake has been found in eastern and southern Iowa. The massasauga was found in a couple of state marshes. The prairie rattlesnake has been seen in the northern portions of the Loess Hills, rarely, and the copperhead can be seen in a small area in southeastern Iowa.