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Are Caterpillars Poisonous?

Missouri Puss Caterpillar on a piece of grass eating.

While most caterpillars are harmless, there are several types of venomous caterpillars in the United States that can cause harm to humans. These include the saddleback moth caterpillar, io moth caterpillar, stinging rose caterpillar, monkey slug caterpillar, and buck moth caterpillar. In Missouri, the flannel moth caterpillar or puss caterpillar can cause the most painful sting and reaction.  


Poisonous caterpillars vs. venomous caterpillars–what’s the difference? 

Great question and an important distinction! It’s important to know the difference in case someone bites into something poisonous or is bitten by something venomous. When you call the poison center, they will ask how you or your family member was exposed to the toxin.


Venomous: “Be bitten”

Venomous describes living things that bite or sting to inject their toxins. Venom is a poisonous substance made specifically by the animal and is often delivered through fangs or stingers. A few examples of venomous creatures would be jellyfish, brown recluse spiders, and copperhead snakes. 


Poisonous: “Bite into”

Poisonous means poisons are not directly delivered. Instead, they accumulate within an animal’s tissues or an item’s surface and exert their effects when ingested, inhaled, or absorbed through the skin. Some examples are the poison dart frog, pufferfish, and milkweed.


Are all fuzzy caterpillars poisonous?


As a general rule of safety, any brightly colored caterpillars with spines, bristles, or a fuzzy appearance might be venomous and should not be touched. Although you may know which caterpillars to look out for, it’s difficult to prevent stings since they often feed on the leaves underside, which makes them hard to see. It’s best when working outdoors to wear gloves and long-sleeved clothing to prevent contact with caterpillars.  


Do caterpillars sting or bite? 

Caterpillars release their venom by stinging – but the stings are sometimes called ‘bites.’ Many caterpillars have hairs or spines which are connected to poisonous glands. When they come into contact with human skin, they can cause pain, itching, burning, swelling, and blistering. These stinging caterpillars would be considered venomous.


What poisonous caterpillars are in Missouri?


The caterpillar to be wary of when in Missouri is the Puss Caterpillar. They are small, thin, yellow, and covered with hairs sticking from the sides. Their hair can often resemble fur. 

Other common stinging caterpillars in Missouri include: 

  • Saddleback caterpillar 
  • Stinging rose caterpillar 
  • Buck moth caterpillar 
  • Io moth caterpillar 


What to do if you get stung by a caterpillar?


If you or someone in your family is stung by a caterpillar, you can use any sticky tape to remove the hairs or spines and then gently wash the area with soap and water. If itching occurs, you may use hydrocortisone cream on the skin. Then call the Missouri Poison Center at 1-800-222-1222 to talk with a specially trained nurse or pharmacist for more instructions. The poison center is open all day, every day, for poisoning emergencies and questions. It’s fast, free, and confidential. 

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