The Saddleback Caterpillar is a colorful, poisonous caterpillar native to Eastern North America that can be found on many trees & ornamental plants. Scientifically known as Acharia stimulea, it is covered in spines attached to poison glands. When touched, the tip of the spine breaks off allowing poison to enter causing a very painful sting.
I was inspired to research & write about these caterpillars after feeling the sharp stinging pain one gets by touching one of these colorful monsters! One morning while clearing out some ‘volunteer’ Obedient Plant flowers I was met with pain on my knee. While moving some unwanted plants from the garden to the wheelbarrow, one of the stalks brushed along my leg and bam! I was stung.
Initially I figured I stepped on a bee nest and was being repaid in kind. But when I didn’t see any bee stuck in my leg of flying around, my eyes darted to the plant. And low and behold, I could see the orange spins sticking out behind a half-eaten leaf. I wondered what kind of pain trip I was in for, but when I saw the unmistakable form of the green/red and spikey skin – I immediately knew what species struck me. But, I did not know what I was in for, or what to do next.
That being said, I’m going to tell you everything you NEED to know about the Saddleback Caterpillar. In this article:
- Critical information about the Saddleback Caterpillar
- What is a Saddleback Caterpillar
- What does the Saddleback Caterpillar turn into?
- Native Range of the Saddleback Caterpillar
- What plants host the Saddleback Caterpillar & where does it live
- Final Thoughts
Critical information about the Saddleback Caterpillar
Common symptoms of Saddleback Caterpillar sting
The most common symptom of being stung by a Saddleback Caterpillar is a sharp, stinging pain somewhat worse than a bee sting. Localized redness or swelling may accompany the sting. Pain typically lasts for one to three hours, but could be longer.   The sting of the Saddleback Caterpillar has been rated as 8 out of 10 using the numerical pain rating scale. 
If you are reading this and are in severe pain, know that for the vast majority of people pain, and possibly swelling/redness are the only symptoms they will experience. More severe symptoms are possible, but they are quite rare. I would consider the pain of the Saddleback to be similar to the bite of a Wheel Bug.
In my own experience I felt the pain on a roughly 1-2″ diameter area of my leg, where I made contact with the Saddleback Caterpillar. There was no redness or swelling. The pain was intense at first and then tapered off to nothing about two hours later.
Can a Saddleback Caterpillar sting be fatal?
The venom from a Saddleback Caterpillar is not fatal. In all sources I have found none mention any fatalities, nor direct evidence or case studies of potentially fatal symptoms. I’ve read numerous papers on this topic, far too many. In many of the papers the researchers themselves were stung, sometimes intentionally, sometimes not, but all described a general pain that lasted from one to three hours. This matches my own experience exactly. 
Side effects of a Saddleback Caterpillar sting
Even though it is rare, there is a possibility of some individuals being hypersensitive to the venom resulting in more severe symptoms. Some more severe symptoms that have been documented include migraine headaches, gastrointestinal discomfort/pain, asthma complications, anaphylactic shock, the rupturing of red blood cells and hemorrhaging. 
How common are severe symptoms?
The frequency of severe symptoms is difficult to assess, as many people stung by caterpillars may not even be aware of *what* stung them, and therefore many incidents are not reported, or assessed to be from a Saddleback Caterpillar. Or they are diagnosed as other bites/stings.
Several sources I read did state that anaphylaxis may occur, and provided a source.  I found no direct cases reporting this condition though. Anaphylactic shock is a potentially fatal allergic reaction. All sources seemed to point to one paper from Brooks Airforce Base in Texas in 1982. I was unable to locate that source in any form. But since other peer reviewed sources cited it I must err on the side of caution and inform you.
*Note – for those curious, the specific citation I was unable to locate is the following: “USAF. 1982. Urticating caterpillars. USAFSAM/EKS, Brooks Air Force Base, TX. pp. 1-3”. I was unable to locate any copy or form. If someone out there manages to find it, I would love to hear about it.
Treating Saddleback Caterpillar stings
The primary treatment for Saddleback Caterpillar stings is to remove any spine tips that may be engorged in the skin and then wash the area with soap and water. This will be all that is necessary for most people.
- If the caterpillar is on you, or on your skin, remove it using a stick. Don’t use your hands.
- Place adhesive tape over the effected area, sticky side down. Duct tape works well, but anything that is ‘sticky’ should work.
- Remove the tape and inspect the area if any spines are still in the skin.
- You may need to repeat with a fresh piece of tape if spines or hairs remain.
- Wash the effected area with soap and water
- Applying a hydrocortisone cream may help with any swelling. Using an icepack may also help with pain and swelling.
When to seek medical attention
If you are stung by a Saddleback Caterpillar, the most important thing you can do to treat your symptoms is to remove any spines that may be lodged in your skin using adhesive tape. If you suspect you’ve been stung by a Saddleback Caterpillar, you may always contact the poison control center at 1-800-222-1222 for advice. If you are experiencing any other symptoms beyond pain you can consult with your physician. 
What is a Saddleback Caterpillar?
A member of the Slug Caterpillar Family, Limacodidae, the Saddleback Caterpillar takes it’s common name from the red oval marking in the middle of it’s green back, in that it resembles a saddle. As with all caterpillars, the Saddleback is the larvae stage of a moth. The Latin name of the Saddleback Caterpillar is Acharia stimulea. 
Mature Saddleback caterpillars are brightly colored. It almost looks like a green blanket has been draped over a reddish brown body with a tiny red ‘saddle’ in the center. Each end will have a pair (or more) of spiny protrusions that are clearly visible. The spines on these are connected to a venom gland that will deposit some poison into anyone via the sharp spine. And I can tell you from personal experience, it hurts! 
On one end of the caterpillar are several green spots that resemble a face. This is actually the posterior of the caterpillar, and the head is at the other end. So this is a false face to confuse predators. A somewhat common tactic used by other caterpillars.
The legs of the saddleback caterpillar is hidden under the body. Additionally they have suckers and also secrete a fluid-like silk as the move on a leaf. The silk helps form an adhesive bond, and the caterpillar therefore slowly glides on the leaf, similar to slugs. Hence the ‘slug caterpillar family’ Limacodidae makes sense. 
The spines on their bodies are a product of evolution to dissuade predators. And research has shown that ‘generalist’ predators such as Assassin Bugs and Paper Wasps will leave these insects alone, as the conclusions were Saddleback Caterpillars had higher survival rates than less-spiny caterpillars.  Other predators also stopped ‘inspecting’ Saddleback Caterpillars, showing that they perhaps ‘learned’ that their spines were dangerous.
Lifecycle of a Saddleback Caterpillar
Like all caterpillars, Saddleback Caterpillars begin life as one of 30-50 eggs laid by an adult female moth. Adult Saddleback moths will lay their eggs on the upper side of a leaf on a host plant in clusters. After approximately 10 days of incubation time, the larvae will chew a hole and exit the egg. Afterwards it will take approximately 4-5 months of feeding before forming a spherical cocoon and pupating. Caterpillars in northern or temperate climates will overwinter as pupae in cocoons. While inside the cocoon, the Saddleback Caterpillar is turning into an adult moth.  
What does a Saddleback Caterpillar turn into?
A Saddleback Caterpillar will turn into a moth. If it is located in the tropic native range it will do so rather quickly, while in temperate regions it will spend the Winter in it’s cocoon.
What eats the Saddleback Caterpillar?
Despite the poisonous spines, Saddleback Caterpillars are able to be killed and consumed by various insect predators such as the Assassin Bug and the Paper Wasp. As previously described, generalist predators will prefer a caterpillar without spines.  So, while the poisonous spines of the Saddleback Caterpillar help dissuade predation they do not fully prevent it.
A major threat to the Saddleback Caterpillar is the Braconid wasp Cotesia empretiae. This wasp will lay eggs into the caterpillar, and these eggs will act as parasites eating the Saddleback from the inside. 
Native Range of the Saddleback Caterpillar
The Saddleback Caterpillar’s native range is Eastern North America. For it’s range in the United States and Canada, one could describe the range by drawing a diagonal line from Texas to Wisconsin, and then head east to the Atlantic Ocean. In addition to the US & Southern Ontario, the Saddleback Caterpillar is also native to Mexico near the gulf coast and the Yucatan Peninsula as well as the Caribbean Islands. 
Host Plants of the Saddleback Caterpillar
Saddleback Caterpillars primarily feed on trees, but can also be found on ornamental plants. You can find a long list of host plants for the Saddleback Caterpillar below. Even though this list is long, it is by no means exhaustive, so in late Summer protect yourself if venturing into brush as these caterpillars can show up in unexpected places and plants.
|Acer spp.||Maple trees|
|Adonidia merrilli||Christmas palm|
|Anthurium andraeanum||Flamingo flower|
|Antigonon leptopus||Coral vine|
|Archontophoenix alexandrae||Alexander palm|
|Baptisia australis||Blue False Indigo|
|Beaucarnea recurvata||Ponytail Palm|
|Canna indica||Indian shot|
|Caryota mitis||Fishtail palm|
|Citrus aurantium||Bitter orange|
|Citrus sinensis||Sweet orange|
|Coccoloba uvifera||Sea grape|
|Cocos nucifera||Coconut palm|
|Coffea arabica||Mountain coffee|
|Cordyline terminalis||Cabbage tree|
|Cycas revoluta||Cycad, sago ‘palm’|
|D. fragrans cornstalk dracaena||Dracaena|
|D. marginata||Dragon tree|
|Dendrobium nobile||Noble dendrobium|
|Dictyosperma album||Princess palm|
|Dracaena deremensis||Green dracaena|
|Dypsis lutescens||Butterfly palm|
|Epipremnum spp.||Pothos vine|
|Feijoa sellowiana||Pineapple guava|
|Ficus elastica||Rubber fig|
|H. syriacus||Rose of Sharon|
|Helianthus spp.||Sunflower and artichoke|
|Hibiscus rosa-sinensis||Chinese hibiscus|
|Ixora coccinea||Jungle geranium|
|Lagerstroemia indica||Crape myrtle|
|Leea coccinea||Hawaiian Holly|
|Macadamia tetraphylla||Macadamia nut|
|Malpighia glabra||Barbados cherry|
|Malus pumila||Common apple|
|Malvaviscus spp.||Wax mallow|
|Melaleuca quinquenervia||Broad leaved paperbark|
|Nannorrhops ritchiana||Mazari palm|
|Phoenix canariensis||Canary Island date palm|
|Phoenix roebeleni||Pygmy date palm|
|Photinia spp.||Red tip|
|Phytotesia virginiana||Obedient Plant|
|Prunus serotina||Black cherry|
|Psidium cattleianum||Strawberry guava|
|Schinus terebinthifoilus||Brazilian peppertree|
|Sideroxylon lanuginosum||False buckthorn|
|Spathoglottis plicata||Large purple orchid|
|Strelitzia nicolai||Great white bird of paradise|
|Swietenia mahogani||West Indies mahogany|
|Syagrus romanzoffianum||Queen palm|
|Syzygium spp.||Brush cherry|
|Tabebuia aurea||Caribbean trumpet tree|
|T. umbellata Ipê||Ipe tree|
|Vitis spp. grapevine|
|Washingtonia robusta||Mexican fan palm|
|Zea mays||Sweet corn|
The Saddleback Caterpillar is a somewhat unwelcome friend in the garden. It is not that common, but common enough to warrant us to be a bit cautious. I’ve lived in my current home for 6 years, and have encountered exactly one caterpillar. None the less, the sting was painful enough that I may begin scanning plants more when I venture into a thickly planted garden in shorts!
Although painful, their sting is not life threatening. But like all natives, they have evolved to have their place in our ecosystem. And, they do try to warn us not to touch them with their bright colors. Either way, I will look a bit closer before I blindly reach into my plants!
 – Carter Reid Ellis, M. D., et al. “What’s Eating You? Caterpillars.” Cutis 108 (2021): 346-351.
 – Hossler, Eric W. “Caterpillars and moths.” Dermatologic therapy 22.4 (2009): 353-366.
 – Torrents, Romain, et al. “Unusual Sting by a Nonindigenous Caterpillar in Europe.” Wilderness & Environmental Medicine 33.1 (2022): 125-127.
 – Villas-Boas, Isadora Maria, Giuliano Bonfa, and Denise V. Tambourgi. “Venomous caterpillars: from inoculation apparatus to venom composition and envenomation.” Toxicon 153 (2018): 39-52.
 – Hossler, Eric W. “Caterpillars and moths.” Dermatologic therapy 22.4 (2009): 353-366.
 – Bibbs, C. S. and J. H. Frank. Acharia stimulea (Clemens) (Insecta: Lepidoptera: Limacodidae). EENY-522. University of Florida IFAS. 2012
 – Biery, Terry L. Venomous Arthropod Handbook: Envenomization Symptoms/treatment, Identification, Biology and Control. No. 43. Disease Surveillance Branch, Epidemiology Division, USAF School of Aerospace Medicine, Aerospace Medical Division (AFSC), 1977.
 – Poison Control Center
 – Sturtevant, Robert S. “The Saddleback Caterpillar. A Minor Pest of Irises and Irisarians”. DeLeon Springs, Fla., American Iris Society, 1920. pp.65
 – Wagner, David L. Caterpillars of Eastern North America : a guide to identification and natural history, Princeton, N.J. : Princeton University Press, 2005, pp.52
 – Tallamy, Douglas W. Bringing Nature Home, Portland : Timber Press, 2009. pp 161, 327.
 – Dellinger, Theresa A., and Eric R. Day. “Stinging Caterpillars: Slug Caterpillars and Flannel Moths.” (2014).
 – [predator evolution spines protect] – Murphy, Shannon M., et al. “Stinging spines protect slug caterpillars (Limacodidae) from multiple generalist predators.” Behavioral Ecology 21.1 (2010): 153-160.
 – Orenstein, Ronald I. Butterflies, Richmond Hill, Ontario : Firefly Books, 2015, pp. 265
 – J. B. Heppner. “Urticating Caterpillars in Florida: 2. Slug Caterpillars (Lepidoptera: Limacodidae)“. Entomology Circular no. 372. Florida Department of Agric. & Consumer Services. 1995
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