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Saddleback Caterpillars: Admire Them From a Distance

Dorothy is a Master Gardener, former newspaper reporter, and the author of several books. Michael is a landscape/nature photographer in NM.

You Can Look But You'd Better Not Touch

You might be better off telling your children that these saddleback caterpillars are worse than poison ivy, which they are.  They are cute, but have hundreds of tiny little hairs that they can leave stuck in your skin, along with painful toxins.

You might be better off telling your children that these saddleback caterpillars are worse than poison ivy, which they are. They are cute, but have hundreds of tiny little hairs that they can leave stuck in your skin, along with painful toxins.

Unmistakable, Cute and Venomous

A saddleback caterpillar (Acharia stimulea) is rarely mistaken for any other caterpillar, and they are very cute, but don't be fooled and try to pick one up because this caterpillar has hairs all over its body that secrete an extremely irritating venom. The saddleback caterpillar is very distinct with its white-ringed brown dot squarely in the center of its green back which resembles a saddle and it is brown at either end (with a pair of nasty-looking, fleshy horns).

If you come into contact with the hairs they will likely cause a very painful rash, burning, itching, swelling and blistering, along with nausea. The venom can spread if the hairs are not removed from the skin quickly. A saddleback caterpillar's cocoon can also have irritating hairs, and you should always be aware that even one hair from the larva can cause irritating, painful rash. The hollow quills are connected to poison glands beneath its skin so if you come in contact with it, the pain can be much worse than the sting of a bee.

The best thing to do is avoid all caterpillars (many of them have hairs or spines), but if you do come in contact with one, the ideal way to remove the hairs from your skin is to apply tape to the skin, then remove it, which should strip away the irritating spines and hairs.

After removing the hairs, wash the area thoroughly with soap and water. If the area itches, you can apply a paste of baking soda and water or hydrocortisone cream. If neither of those work, you might try an antihistamine cream although some people have skin reactions to those, so use them only as a last resort.

If the result is a severe blister, you need to contact your doctor about a tetanus booster if your shots are not up to date.

Maybe He's Only Cute From a Distance

Seeing the hairs on the saddleback caterpillar up close in the larvae stage makes it easier to understand why people should not pick them up.  Check out the sharp ends of the hairs, all of which are loaded with irritating venom.

Seeing the hairs on the saddleback caterpillar up close in the larvae stage makes it easier to understand why people should not pick them up. Check out the sharp ends of the hairs, all of which are loaded with irritating venom.

Native to the Eastern United States

The one-inch-long saddleback caterpillar is the larval form of a fuzzy, dark brown moth. It is native to a large area of eastern United States where it feeds on a wide variety of host plant species. In northern temperate areas and warmer southern climates, however, this little guy doesn't do well. Most people consider this species of caterpillar to be medically significant and a pest at the same time, although it appears to have minimal effects on landscapes and in agriculture.

In the United States, these caterpillars have been found from Massachusetts south to Florida and west to eastern Missouri and Texas. Outside the United States, they are also found in Mexico, Central America, and Colombia.

Dorsal view of a saddleback caterpillar moth.

Dorsal view of a saddleback caterpillar moth.

Descriptions of Stages

Adult caterpillar - An adult saddleback caterpillar is glossy dark brown in color with some black shading, and dense scales can be seen on the body and wings, which makes it look very furry. The hind wings are a lighter, paler brown than the forewings. The wingspan ranges from about an inch to almost two inches wide, and females are typically larger than males. Near the forewing base is a single white dot; and near the forewing apex, up to three more white dots can be seen.

Eggs - The female saddleback caterpillar lays her eggs in irregular clusters of up to 50 eggs on the top side of host plant leaves. Sometimes, the eggs, which are very tiny, (usually no more than .08 inches) may overlap each other. They are transparent and yellow, with a scaly look and thin edges.

The larval stage - The saddleback caterpillar has a slug-like body that is truncated. Concealed under the ventral surface of the caterpillar's body are the fleshy prolegs. The bright colors are considered warnings to all that this guy is distasteful and toxic (aposematic coloration). Dark brown on the anterior and posterior ends, this caterpillar has a contrasting bright green blanket pattern on its dorsal midsection. The green area is bordered with white marks that create a saddle shape. The skin in the larval stage has a granulated texture, with large protuberances extending from both the front and back, each of which is covered in long, bristle-like structures in which the spines are embedded.

Saddlebacks in Motion

Tips

  • Avoid any areas infested with caterpillars whenever possible.
  • Always wear gloves (and a hat) when gardening.
  • Never touch a caterpillar with your bare hands. If one gets stuck to your skin, use a stick or some other tool to remove it.
  • Teach young children early about the danger of caterpillars.
  • Be aware that these caterpillars often feed on the underside of leaves and avoid brushing against them.

References

Paraska KK. Caterpillar stings – a case study. AAOHN J. 2009;57:402-403

© 2018 Mike and Dorothy McKenney