Saddleback Caterpillar: Essential Facts and Tips

The Saddleback Caterpillar is a fascinating creature that might pique your curiosity. As the larval stage of a limacodid or slug moth (Acharia stimulea), this bright green caterpillar stands out with its brownish-purple spot in the middle of its back that resembles a saddle, hence its name Packsaddle Caterpillars. Native to a variety of trees and shrubs, Saddleback Caterpillars have some distinct features that make them an interesting subject to explore.

One of the most important things you should know about these caterpillars is that they come with a bit of a sting – literally. The spines on their body contain venom that can cause irritation and pain if you come into contact with them. So, while you may be intrigued by the vibrant color and unique appearance of the Saddleback Caterpillar, it’s best to appreciate them from a distance.

Overview

The Saddleback Caterpillar, scientifically known as Acharia stimulea, is a unique and colorful member of the Limacodidae family within the Lepidoptera order. They are commonly referred to as “slug caterpillars” due to their slug-like appearance.

These caterpillars are known for their distinct markings, which include a purplish-brown “saddle” on their bright green backs. They can be found feeding on the leaves of various trees and shrubs, such as basswood, chestnut, cherry, plum, and oak. Generally, Saddleback Caterpillars appear during late summer.

Here are some key characteristics of the Saddleback Caterpillar:

• Belongs to the Limacodidae family in the Lepidoptera order
• Unique appearance: bright green body with purplish-brown “saddle”
• Commonly found on leaves of basswood, chestnut, cherry, plum, and oak trees

The life cycle of these fascinating creatures spans over several months. They need approximately four to five months to feed and develop, eventually pupating and transforming into the Saddleback Caterpillar Moth.

It’s important to handle these beautiful caterpillars with caution. They are equipped with urticating hairs on their knobs, which can cause painful stinging reactions upon contact with human skin.

In summary, the Saddleback Caterpillar provides a striking example of nature’s diverse beauty. Unique in appearance and an intriguing member of the slug caterpillar family, they play a role in our natural environment. Just remember to admire them from a safe distance to avoid any unwanted consequences.

Physical Characteristics

Body Features

The Saddleback Caterpillar is easily identifiable by its unique appearance. Its body is covered in spines and hairs, making it a bit intimidating to look at. It has an opaque green coloration, with translucent lime green edges, giving it a vibrant appearance. Additionally, you’ll notice green protuberances around the body. The most striking feature is the saddle-like pattern on its back, characterized by a brownish-purple spot that resembles a saddle on a horse.

• Spines: Sharp and venomous, providing protection from predators
• Hairs: Abundant and spread across the body
• Color: Opaque green, translucent lime green edges, and brownish-purple saddle

Wings and Flying

The adult Saddleback Caterpillar turns into a moth. Its moth stage, known as Acharia stimulea, has forewings and hindwings. The forewings are typically brown, while the hindwings are lighter in color. Additionally, the moth is quite fuzzy, with small white spots scattered across its wings. The wingspan of the moth ranges between 20 to 25 mm.

Here’s a comparison table of the Saddleback Caterpillar’s physical characteristics:

Remember to be cautious while observing these beautiful creatures, as their spines can contain venom that may cause skin irritation. Overall, the Saddleback Caterpillar and its moth stage are quite unique in their physical attributes, making them an interesting species to study and appreciate.

Life Cycle and Habitat

The life cycle of the Saddleback Caterpillar starts with eggs. These small eggs hatch into larvae, which go through several instar stages, growing larger and more developed with each molt.

As they mature, Saddleback Caterpillars spin tough silk cocoons before entering the pupa stage. They overwinter in these cocoons, eventually emerging as adult moths. The entire life cycle and biology is fascinating and unique to this species.

Their habitat spans across Eastern North America. You can find them munching on the leaves of various trees and shrubs such as basswood, chestnut, cherry, plum, and oak. They show up typically in late summer, making the most of their favorite leafy snacks.

Here are some key characteristics to remember:

• Life cycle stages include egg, larva, pupa, and adult moth.
• Multiple instar stages during larval development.
• Spin silk cocoons for overwintering.
• Found primarily in Eastern North America.
• Primarily feed on the leaves of trees and shrubs.

So if you’re out exploring the woodlands of Eastern North America, keep an eye out for these striking caterpillars. Just watch out for their stinging hairs, as they can cause a painful reaction if touched. Enjoy observing their interesting life cycle and remember, you’re getting a glimpse into one of nature’s many wonders.

Diet and Host Plants

Saddleback caterpillars are known to feed on a variety of host plants. You can find them munching on leaves of trees like oak, cherry, basswood, elm, plum, chestnut, maple, and hackberry. They also consume foliage from shrubs such as spicebush, mountain coffee, grapevine, holly, and false buckthorn.

These caterpillars aren’t too picky and have been found on sweet corn as well. In your garden, they might cause minor damage to ornamental plants, but don’t worry, they usually don’t pose a significant threat.

Here is a brief list of common host plants for the Saddleback caterpillar:

• Oak
• Cherry
• Basswood
• Elm
• Plum
• Chestnut
• Maple
• Hackberry
• Spicebush
• Mountain coffee
• Grapevine
• Holly
• Sweet corn
• False buckthorn

Remember, it’s essential to identify the plants in your garden or surrounding areas. This way, you’ll be more aware of the potential presence of Saddleback caterpillars and better equipped to manage their impact on your green spaces.

Defense Mechanism and Predators

Saddleback Caterpillar’s Defense Mechanism

Saddleback caterpillars have unique defense mechanisms to protect themselves. One of them is urticating hairs.

• They bear urticating hairs on four prominent knobs at the front and rear, and on smaller knobs along the sides.

These hairs contain venom, which can cause a painful sting if touched. In some cases, their sting might be more painful than a bee sting. Their poison glands produce toxins to deter their predators.

Predators of Saddleback Caterpillar

Despite their defenses, saddleback caterpillars do have predators, one being the braconid wasp.

• Braconid wasps are parasitic insects, laying their eggs inside the caterpillar.
• When the eggs hatch, the larvae consume the caterpillar from the inside, eventually killing it.

By understanding the defense mechanisms and predators of saddleback caterpillars, you become more aware of this fascinating yet potentially dangerous creature. Always exercise caution when interacting with them and be mindful of their urticating hairs.

Danger to Humans

Sting Reactions

Saddleback caterpillars are known for their painful stings. When you accidentally touch or brush against their spines, you may experience a range of symptoms, including:

• Pain: The sting can cause severe pain, lasting from several minutes to hours.
• Redness, rash, and itching: It’s common for the stung area to become red, swollen, and itchy.
• Difficulty breathing and anaphylactic shock: In rare cases, individuals with severe allergies or asthma complications might experience difficulty breathing or even anaphylactic shock.

Remedies and Treatments

If you’ve been stung by a saddleback caterpillar, there are several treatments you can try to alleviate the pain and other symptoms:

1. Removing spines: Use adhesive tape to gently pull out the spines from your skin.
2. Cleaning the area: Wash the affected area with soap and water to prevent infection.

Conclusion

Saddleback caterpillars, belonging to the slug caterpillar family, are unique creatures that capture attention with their distinct appearance. These caterpillars have a length of about 3/4 inch when mature, and their bodies feature four prominent knobs at the front and rear, as well as smaller knobs along the sides¹. Their fascinating coloration includes a translucent yellow, with a dark purple saddle-like marking on their back.

Living up to their slug caterpillar name, you’ll notice that they don’t have the familiar legs often seen on other caterpillars. Instead, their movement relies on the underside of their body.

Now let’s talk about their metamorphosis. These caterpillars create silk cocoons¹ for themselves to sustain the colder months. After some time, they emerge as moths. The adult moths are fuzzy and dark brown, differing greatly from the vibrant appearance of their juvenile form.

In summary, saddleback caterpillars are intriguing creatures with distinct physical characteristics. Becoming familiar with their key features – their vibrant colors, legless body, and silk cocoons – and understanding their transformation into moths helps you appreciate their role in our ecosystem. So, next time you come across one of these unique critters, remember these fascinating facts about them.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Possibly Saddleback Caterpillar Moth

Subject: Bizarre moth mimicking crayfish
Location: Columbia, NJ
July 1, 2014 5:22 am
We saw this moth on our camper near the Delaware Water Gap, it looked odd, when it flew a short distance and landed it took on a completely different shape…a tiny crayfish! How does a moth evolve to mimick such a creature?
Signature: SeanK

Dear SeanK,
The illusion you describe is quite effective, and the outline of this moth does look like a Crayfish.  We wish your image had more detail.  Our best guess is possibly a Saddleback Caterpillar Moth, Acharia stimulea, which is also pictured on BugGuide.

Letter 2 – Saddleback Caterpillar

Hello Bugman,
My wife found this really awesome caterpillar a few days ago on her Gerber Daisies. I have been looking all over the Internet trying to identify it, when I stumbled across you site. It looks like someone has asked you about a particular “Saddleback Caterpillar”, and that seems to fit the description of the picture I’m sending you now. Is that what this is? Thanks for your help!
Gray Benton
Iron Station, North Carolina

Hi Gray,
Yes, indeed, you have a Saddleback Caterpillar, Sibine stimulea. Beware those poisonous spines. They can cause quite a bit or irritation. Holland writes: “Nettles are not to be compared in stinging power to the armament of this beautifully colored larva.” Thanks for the photo and I’m so glad our site was helpful.

Letter 3 – Saddleback Caterpillar

Prickly Stinging Bug
Location:  Atlanta, GA
August 10, 2010 6:08 am
We found a bug that stings and looks kind of like a sand spur you find at the beach.
We found tree of these bugs on the blades of some tall ornamental grass.
On each end there are little brown spurs and in the middle there is a marking that looks like an eye.
Could be some sort of caterpillar but it doesn’t seem to move while watching it.
Total length is about a quarter inch and about half as wide as it is long.
Any idea’s.
Ken

Hi Ken,
The sting of the Saddleback Caterpillar, Acharia stimulea, is quite painful and the effects are reported to be long lasting.

Letter 4 – Saddleback Caterpillar

Subject: What is this Horned Thing?
Location: East of Charlotte, NC
October 27, 2012 6:38 pm
I was pruning our shrubs today and this thing got on the back of my fingers and stung/bit me. It really hurts! Took some Benadryl but am curious as to what this thing is and if I will live until morning! lol!
Signature: Not a Bug Fan

Dear Not a Bug Fan,
You were stung by a Saddleback Caterpillar, Acharia stimulea, and you will live.  Read How to Treat a Caterpillar Sting on WikiHow.  We have never received a photo of the underside of a Saddleback Caterpillar before, Your example is a good illustration of the rationale for calling the family that the Saddleback Caterpillars belongs to, Limacodidae, the Slug Caterpillar Moth family.

Letter 5 – Saddleback Caterpillar

Subject: what the heck is this
Location: fuquay varina nc
September 2, 2013 12:55 pm
Walked past a branch and felt this awful pain in my leg followrd by whelps and redness then very sore. Took this pic. Holy moly what is it
Signature: glenn

Hi Glenn,
The stinging capabilities of the Saddleback Caterpillar, Acharia stimulea, are well documented online.  According to BugGuide:  “Caterpillars are capable of inflicting lasting and painful stings with their spines.”  According to Featured Creatures:  “Acharia stimulea is best known as a medically significant species. The large spines and potent hemolytic venom rank it as one of the most important North American species of urticating caterpillars, with larvae from the moth family Megalopygidae being the only lepidopterans considered more dangerous (Scott 1963, 1964; Durden and Mullen 2009; Hossler 2010).  The spines of A. stimulea are strong, acutely pointed, and hollow. They embed deeply into tissue and break off, and can interrupt healing as the protoplasm from the venom glands dries into the tissue area (Gilmer 1925). The venom itself can cause a systemic condition called erucism or acute urticaria, for which severe symptoms may include migraines, gastrointestinal symptoms, asthma complications, anaphylactic shock, rupturing of erythrocytes, and hemorrhaging (USAF 1982, Hossler 2009).  Physically manifested symptoms may or may not be present with erucism (Hossler 2009). Contact dermatitis caused by A. stimulea includes immediate intense burning sensations around the contact zone, arector pili muscles tightening causing hair to stand on end, increased perspiration in the affected area, red blanching of the skin, and blistering (Edwards et al. 1986; Hossler 2009, 2010). Symptoms can last for five hours, and leave red blotches in the envenomation site (Hossler 2009).”

Letter 6 – Saddleback Caterpillar

Subject: Very Strange Bug
Location: Clinton, Ohio
September 5, 2015 12:26 pm
I found this today on my compost lid. The bug looks like it is wearing a lime green coat with a white fringe. It also looks like it has large lime green eyes and a red nose unless I am looking at the back end of that bug.
Signature: J. Alberts

Dear J. Alberts,
This distinctive caterpillar is called a Saddleback Caterpillar, Acharia stimulea, and it should be handled with caution because they are capable of stinging.

Letter 7 – Saddleback Caterpillar

Subject: Need help identifying what bit me
Location: Northeast
September 26, 2015 5:13 pm
Hello Bugman. I was gardening and was bit by the centipede (?) viewed in the attached photo. It was on the underside of a Manhattan Euonymus and attached to the leaf by what appears to be a bright green vest. This happened in East Setauket, New York (located in Suffolk County on Long Island).
I had extreme pain and a burning sensation that traveled up my arm for about six inches.
Can you identify what this is? Thank you for any guidance you can offer.
Signature: Krista

Dear Krista,
You were not bitten, but rather stung by this Saddleback Caterpillar, Acharia stimulea, a species found in much of eastern North America.  According to BugGuide:  “Caterpillars are capable of inflicting lasting and painful stings with their spines.”

Letter 8 – Saddleback Caterpillar

Subject: What is this thing???
Location: South jersey
August 17, 2017 3:34 pm
My friend found this little critter in his yard here in southern New Jersey. It bit him and almost 2 hours later his arm is JUST now going back to normal. What is this?
Signature: Erin

Dear Erin,
We suspect the next time your friend encounters a Saddleback Caterpillar, your friend will look and not touch, since that is the best way to interact with Stinging Slug Caterpillars from the family Limacodidae.