What Does a Saddleback Caterpillar Turn Into? Unveiling the Mystery Transformation

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Saddleback caterpillars may catch your attention due to their intriguing and unique appearance. These bright green caterpillars are easily identifiable by the brownish-purple spot in the middle of their backs, which resembles a saddle. You might wonder what these fascinating creatures turn into as they progress through their life cycle.

These caterpillars are actually the larval stage of the limacodid or slug moth (Acharia stimulea). As they mature, they go through a transformation process that leads them to become fully-formed moths. These moths, unlike their vibrant and distinctive caterpillar stage, have a more subdued appearance, being fuzzy and dark brown with some cinnamon and tiny white spots 1.

In the course of their development, saddleback caterpillars feed on the leaves of various trees and shrubs, like basswood, chestnut, cherry, plum, and oak. They predominantly appear in late summer and eventually form cocoons. From these cocoons, the moths emerge the following spring and summer, ready to continue the cycle by laying their eggs on the upper surface of leaves 2.

Identification and Appearance

Color and Size

When identifying a saddleback caterpillar, it’s essential to note its distinct colors and size. These caterpillars have a bright green body with a brownish or yellow face and measure about 1 inch in length. Interestingly, the adult moths that emerge from the larval stage are glossy dark brown in color, with some black shading and a white dot near the forewing base.

Unique Features

Saddleback caterpillars possess some unique features that make them easily identifiable. Here are some of their key characteristics:

  • A striking green saddlecloth on their back with a purplish-brown saddle in the middle
  • Rows of urticating spines surrounding the saddle
  • Larval stage of a limacodid or slug moth
  • Can be found on various trees and shrubs

One crucial aspect to remember is that saddleback caterpillars are poisonous, with their spines capable of causing painful stings. So, if you ever come across one, be cautious and avoid handling them directly.

In summary, when identifying a saddleback caterpillar, pay close attention to its color, size, and the unique features mentioned above. By being aware of these characteristics, you’ll be better equipped to spot and avoid these potentially harmful creatures.

Habitat and Range

The saddleback caterpillar, also known as the packsaddle caterpillar, can be found in a wide range across eastern North America. They inhabit areas from Florida to Texas and even reach the northern parts of the continent. Throughout their range, these caterpillars can be found living on a variety of host plants that provide the necessary environment for growth and development.

Some of the common host plants where you may spot a saddleback caterpillar include:

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

In their natural habitat, saddleback caterpillars are not confined to a single type of plant. They can survive and thrive on a diverse range of vegetation, which makes them a resilient species that easily adapts to changes in their environment. This adaptability has contributed to their widespread presence across North America.

In northern temperate areas as well as warmer southern climates, the saddleback caterpillar has not only made its presence known but also established itself as a medically significant pest. While their impact in landscaping and agriculture might be considered minor, it is crucial to be aware of them and take necessary precautions when coming across one in your garden or an outdoor space.

Stinging Mechanism and Symptoms

Contact and Reaction

When you accidentally touch a saddleback caterpillar, their hollow spines release toxins that cause a variety of symptoms. The initial reaction to a sting typically includes a burning or stinging sensation, followed by redness and inflammation1. More severe symptoms can occur, such as:

  • Swelling
  • Nausea
  • Asthma
  • Anaphylactic shock (in rare cases)

These caterpillar stings are generally milder than those of other stinging insects, but individual reactions may vary2.


Imagine brushing against a leaf hosting a saddleback caterpillar. You instantly feel a painful sensation in your skin, which may develop into a red, swollen area.

Medical Treatment

In case of a sting, it’s essential to act promptly. Remove any remaining spines from your skin using a strip of adhesive tape3. To alleviate the pain and reduce inflammation, apply ice or a cold pack to the affected area4. Although the majority of caterpillar stings are mild, the symptoms can range from mild to severe. If you experience severe symptoms or an allergic reaction, seek immediate medical assistance5.

Mild Symptoms Severe Symptoms
Painful sensation Hemorrhaging
Redness Allergic Reaction
Swelling Nausea
Anaphylactic Shock

You should be aware that each person’s reaction to a saddleback caterpillar sting is different. For some, the pain and inflammation may subside quickly, while others may require medical attention for more severe symptoms or allergic reactions.

Life Cycle and Metamorphosis

From Egg to Caterpillar

You begin by discovering the early stages of the saddleback caterpillar’s life. The species, known scientifically as Acharia stimulea, starts as an egg. After hatching, the larvae emerge and become saddleback caterpillars. During the larvae stage, they go through multiple growth phases, which includes feeding on leaves and developing defense mechanisms.

It is fascinating that these caterpillars have unique features like suckers for better mobility, making them stand out from the rest. Want to know more? Let’s move on to the next stage.

Caterpillar to Moth

The magic happens when saddleback caterpillars prepare to transform into moths. They start building a sturdy silk cocoon in which they undergo metamorphosis. Inside the cocoon, the pupa forms and the adult moth of Acharia stimulea (Clemens) will finally emerge.

What should you expect from the adult moths? Both male and female moths are fuzzy, usually dark brown. It’s important to remember that adult moths do not retain the stinging hairs they had as caterpillars. Now you know more about the life cycle and metamorphosis of the fascinating saddleback caterpillar into a moth!

Diet and Host Plants

Saddleback caterpillars are known for their broad diet and variety of host plants. These green critters are actually the larval stage of the limacodid or slug moth, known scientifically as Acharia stimulea1. They can be found feeding on a wide range of trees and shrubs2.

During their larval stage, saddleback caterpillars can feed on several host plants. Some examples include:

  • Citrus trees2
  • Cherry trees3
  • Corn plants4

As they mature, saddleback caterpillars progress through different instar stages4. The final instar is when they are most likely to cause the most noticeable damage to their host plants, as they consume the entire leaf5. Keep an eye out for these pests and make sure to protect your plants in a timely manner.

Predators and Defense Mechanism

Saddleback caterpillars have impressive defense mechanisms to deter predators. They possess urticating hairs and poison glands, which make them one of the stinging caterpillars.

Urticating Hairs and Poison Glands

These hairs deliver a painful sting when touched and can cause severe skin irritation. The poison glands produce venom, which makes the caterpillar even more dangerous to predators. Here are some features of their defense:

  • Urticating hairs on prominent knobs
  • Venomous poison glands
  • Painful sting and severe skin irritation

Predators like birds and insects might try to attack saddleback caterpillars, but their defense mechanisms deter them effectively. Remember to avoid contact with these caterpillars, as you might experience a painful sting too.

Sightings and Experiences

Saddleback caterpillars are known for their bright green color and distinctive saddle-like marking on their back. You may have seen these caterpillars in your garden, munching on leaves. They are part of the Limacodidae family and grow to be about an inch long.

They have a peculiar appearance, with four prominent knobs at the front and rear, as well as smaller knobs along their sides. These knobs are covered in urticating hairs that can cause painful stinging if you accidentally touch them.

Although caterpillars don’t have conventional eyes or ears like other animals, they do have simple eye structures called ocelli and can detect light and shadows. They also have unique legs compared to other caterpillars. Saddleback caterpillars have modified prolegs with suckers instead of crochets, which help them attach to surfaces for feeding and support.

You might mistake their appearance for a snake or other creature due to the saddle marking on their back. This marking is brownish-purple, located near the apex, giving them an interesting face-like appearance.

In summary, here are a few key features of the saddleback caterpillar:

  • Bright green color with a brownish-purple saddle marking
  • Inch long, part of the Limacodidae family
  • Knobs with urticating hairs that cause painful stinging
  • Ocelli for detecting light and shadows
  • Modified prolegs with suckers

Next time you spot one of these fascinating saddleback caterpillars, take a moment to appreciate their unique characteristics. But remember to keep your distance to avoid their painful sting!


  1. Stinging and Venomous Caterpillars – Gardening Solutions 2

  2. Stinging Caterpillars on Shrubs – University of Maryland Extension 2 3

  3. Packsaddle Caterpillars | Home & Garden Information Center 2

  4. Saddleback Caterpillar | NC State Extension Publications 2 3

  5. Start looking out for stinging caterpillars – AgriLife Today 2

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 – Saddleback Caterpillar


caterpillar that stings
I found this bug on my blueberry bushes and it stung me. I thought it was stinging nettles but on closer look found this bug. What’s that bug?

Hi Nancy,
This is a Saddleback Caterpillar and yes, it does sting.

Letter 2 – Saddleback Caterpillar


What is this?
Dear Bug experts,
I just got stung while taking a photo of this. What is it and should I be worried?
Anne Cracraft
Knoxville, TN

Hi Anne,
Fear not. You will live. The sting of the Saddleback Caterpillar is only a mild skin irritant. Had you scrolled down our homepage, you could have identified it for yourself. We will now replace that photo with yours.

Letter 3 – Saddleback Caterpillar


saddleback vs. inchworm
What a fantastic site you have! Love all of the photos. I have a bug behavior question for you and possibly a photo for your carnage page. Several days ago I found a saddleback caterpillar in my yard and put it (along with the weed it was on) into my 5 yr old’s bug house for observation. A few days later my friend brought over some basil from her yard and it had an inchworm on it, so feeling lucky to have a bug house in my kitchen, I put the worm and some of the basil in there with the saddleback. Things seemed fine for several days, then 2 days ago, I noticed that the saddleback was doing laps around and stinging the inchworm. Yesterday my 5 year old pointed out the fact the inchworm is now covered in a web-like pillow of some sort and is apparently dead. What did the saddleback do to the inchworm? Why? Can a saddleback produce a web-like substance? Also, how long before the saddleback metamorphasizes?
Birmingham, Alabama

Hi Donie,
We find the behavior you describe utterly fantastic, and have no explanation. However, we feel you may have misinterpreted the situation. The inchworm you write about appears to be an Omniverous Green Looper, and it also appears to be in the pupal stage. We believe the caterpillar just pupated on its own, without any help from the Saddleback Caterpillar. Most caterpillars can spin silk. We are going to post your Saddleback Caterpillar, Sibine stimulea. The spines on this caterpillar are mildly poisonous and will sting.

Letter 4 – Saddleback Caterpillar


Bug ID Help? Never mind.
My father just got bit by this strange bug on his forehead. This is a photo of the bottom of the bug. What is it? Should he seek medical attention? The bite is red and appears to be sweating just at the bite… otherwise he feels fine.
James in Cape Coral, Florida
I just sent you the email and forgto to attahed the photo. After looking through you wonderful website we found the Saddleback Caterpillar, Sibine stimulea.
Thank you,

Hi James,
Sorry for the delay, but our mailbox is brimming with queries. Glad you found out that your Saddleback Caterpillar, Sibine stimulea, isn’t deadly, just irritating. It doesn’t bite though, it has stinging spines.

Letter 5 – Saddleback Caterpillar


Subject:  Strange bug wearing green vest
Geographic location of the bug:  Westchester County, NY
Date: 09/12/2017
Time: 02:08 PM EDT
Found this strange bug outside our home and have never seen anything like this
How you want your letter signed:  Bug Patrol

Saddleback Caterpillar

Dear Bug Patrol,
Handle with caution.  This is a Stinging Slug Caterpillar known as a Saddleback Caterpillar.

Letter 6 – Saddleback Caterpillar


Subject:  what in the world?
Geographic location of the bug:  Blue Ridge Mtns, NC
Date: 09/23/2018
Time: 08:50 AM EDT
Your letter to the bugman:  found hanging in a tree.  stung head when walked under it.  felt like bee sting.
dont know if its a bug or a flower.
How you want your letter signed:  Bug or Flower?

Saddleback Caterpillar

You were stung by a Saddleback Caterpillar, Acharia stimulea.  According to BugGuide:  “Caterpillars are capable of inflicting lasting and painful stings with their spines.”

Letter 7 – Saddleback Caterpillar


Subject:  1inch worm with stickers
Geographic location of the bug:  Fort Pierce Florida
Date: 09/10/2021
Time: 06:33 PM EDT
Your letter to the bugman:  He was eatting a leaf from bird of paradise.
How you want your letter signed:  Vickie

Saddleback Caterpillar

Dear Vickie,
This is a Saddleback Caterpillar and we did not know they feed on bird of paradise.  According to BugGuide they feed on:  “
Many trees, shrubs, and grasses including apple, asters, blueberries, citrus, corn, dogwoods, elms, grapes, linden, maples, oaks, Prunus species, sunflowers and viburnums. Troy has personally seen them feeding on liriope, cherry, oak, and holly.”  Handle with caution.  The Saddleback Caterpillar has stinging spines.


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

    View all posts
  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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Tags: Saddleback Caterpillars

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