Is it poisonous?

Venomous Caterpillars: A Hidden Danger in Your Backyard


While many people are aware of the dangers posed by poisonous plants and insects, few are as familiar with the hidden threats lurking right in their backyards: venomous caterpillars. They may appear harmless and even cute, but some species pack a painful sting that can lead to serious health consequences. In this article, we’ll explore the world of venomous caterpillars, how to identify them, and what to do if you’re stung.

What Makes a Caterpillar Venomous?

Not all caterpillars are venomous, but the ones that are have a specific feature that sets them apart: urticating hairs or spines. These hair-like structures are connected to poison glands that release venom upon contact. When a person brushes against one of these venomous caterpillars, the hairs break off and embed in the skin, causing an immediate painful reaction. Some species can also shoot these hairs as a defense mechanism, making them an even greater threat in your backyard.

Common Venomous Caterpillars

While there are thousands of caterpillar species, only a small number are venomous. Here are some of the most common venomous caterpillars found in North America:

  • Puss Caterpillar (Megalopyge opercularis): Also known as the Southern flannel moth caterpillar, this fuzzy creature is considered the most venomous caterpillar in the US. It’s covered in a thick coat of hair that conceals venomous spines. Their sting can cause intense pain, burning, swelling, and in some cases, difficulty breathing, chest pain, or anaphylactic shock.
  • Buck Moth Caterpillar (Hemileuca maia): This caterpillar has a single row of venomous spines running down the length of its body, with smaller hairs around it. Stings can cause a stinging, burning sensation, which can last for several hours.
  • Saddleback Caterpillar (Acharia stimulea): Named for the saddle-shaped green patch on its back, this caterpillar has venomous spines projecting from its body. Its sting can cause pain, burning, and swelling, sometimes accompanied by nausea and headache.
  • Io Moth Caterpillar (Automeris io): Covered in clusters of spines, the Io moth caterpillar can inflict a painful sting that causes burning, redness, and swelling.

How to Avoid and Treat Caterpillar Stings

Prevention is the best medicine when it comes to venomous caterpillars. Follow these tips to minimize your risk of being stung:

  1. Learn to identify venomous caterpillars in your area and teach children to avoid them.
  2. Wear protective clothing, such as gloves and long sleeves, when working in the yard or gardening.
  3. Be cautious when moving around any brush piles, logs, or piles of leaves where caterpillars may be hiding.
  4. Don’t touch or handle caterpillars, even if they appear to be harmless.

If you do get stung, follow these steps:

  1. Remove any visible spines or hairs from your skin using tweezers or the sticky side of tape.
  2. Wash the area with soap and water, then apply a cold pack to reduce swelling and pain.
  3. Take an over-the-counter pain reliever and antihistamine to reduce pain and itching.
  4. Monitor the area for signs of infection, such as increased redness, warmth, or pus. If you notice any of these symptoms or have difficulty breathing, chest pain, or a severe allergic reaction, seek immediate medical attention.


Venomous caterpillars may be a hidden danger in your backyard, but with proper precautions and education, you can keep yourself and your family safe. Learn to identify these unique creatures and take steps to avoid contact with them. If you or a family member do get stung, remain calm, follow the necessary steps to alleviate the pain and seek medical attention if necessary.

Frequently Asked Questions

Are all caterpillars venomous?

No, only a small percentage of caterpillars are venomous. Most caterpillars are harmless and pose no threat to humans.

Can venomous caterpillars cause lasting harm?

In most cases, venomous caterpillar stings cause temporary pain and discomfort. However, serious reactions and complications can occur in some cases, such as difficulty breathing, chest pain, or anaphylactic shock.

How can I tell if a caterpillar is venomous?

Venomous caterpillars usually have visible urticating hairs or spines that contain venom. Research and familiarity with the local species in your area will help you recognize the most common venomous caterpillars.

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