Exploring the World of the Monkey Slug: A Brief Overview

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The Monkey Slug, also known as the Hag Moth caterpillar, is a fascinating creature with a peculiar appearance. Known scientifically as Phobetron pithecium, this caterpillar resembles a hairy, disheveled mess rather than its namesake primate.

Primarily found in the eastern United States, the Monkey Slug has a unique, even bizarre, set of features that set it apart from other caterpillars. Some distinctive characteristics include:

  • Six fleshy, hairy projections called “arms”
  • Brown coloration that can help it blend into its surroundings
  • Resemblance to a dead leaf as a form of camouflage

Despite its outlandish appearance, the Monkey Slug is not harmful to humans and eventually transforms into a less intimidating adult moth. Exploring the world of this fascinating creature offers insight into its peculiarities and the marvels of nature.

Monkey Slug Overview

Slug vs Caterpillar

The monkey slug is an interesting creature that is actually a caterpillar, not a slug. Here is a comparison table to showcase their differences:

Aspect Slug Caterpillar
Body Shape Soft, slimy, elongated Segmented, with a distinct head and tail
Legs None; moves using a muscular foot Six legs and several prolegs
Skin Texture Usually slimy Covered in hairs, spines, or projections
Defense Mechanisms Produces mucus Hairs and colorful patterns

Monkey Slug Characteristics

The monkey slug, formally known as Phobetron pithecium, is a unique caterpillar species with interesting features:

  • Covered in long, dense brown setae (hairs)
  • Has tentacle-like projections on the sides
  • Resembles a yellow, furry spider or monkey

These caterpillars are part of the slug caterpillar moth family, which is comprised of various different caterpillar species. Monkey slugs are known for their unusual appearance, as they have six hairy “legs” and three distinct pairs of equally hairy “arms” (projections). Due to their dense hair coverage, they appear to be furry.

Some of the most distinctive characteristics of monkey slugs include:

  • Their six true legs and additional prolegs for movement
  • Spines or setae covering the body, providing a hairy appearance
  • Bright yellow coloration, making them easily noticeable
  • Their unique look, resembling both a monkey and a spider

Life Cycle and Habitat

Eggs and Larvae

The life cycle of the Monkey Slug, also known as the Hag Moth, starts with females laying eggs on the leaves of various plants. The eggs tend to hatch into stinging larvae, better known as caterpillars. These caterpillars are known for their poisonous, stinging hairs and unique appearance, resembling a “mollusk” more than a typical caterpillar.

The larvae primarily feed on a variety of leaves, such as:

  • Wild cherry
  • Oak
  • Apple
  • Willow
  • Sassafras

Adult Moths

Adult Hag Moths are small, inconspicuous silk moths that have a wingspan of about 1-1.5 inches. They can be found in various habitats throughout the eastern United States, including Florida. Their habitat ranges from forests to residential areas.

Habitat Found in Eastern US? Notable Features
Forests Yes Diverse plant species
Residential Yes Fruit trees, gardens

Pros of the Monkey Slug

  • Beneficial species: Moth helps control certain pests.
  • Unique appearance: Fascinating to study and observe.

Cons of the Monkey Slug

  • Stinging hairs: Larvae can cause irritation, swelling, and rash.
  • Potential damage: Larvae can harm foliage of various plants.

Behavior and Diet

Monkey Slug Locomotion

The Monkey Slug, also known as the Hag Moth caterpillar, is a unique type of slug caterpillar due to its appearance and locomotion. Unlike typical moth caterpillars, Monkey Slugs have:

  • Prolegs with suckers for gripping
  • No visible head
  • Long, fleshy tentacles

These attributes allow them to move slowly and cling onto leaves and plants.

Comparison Table: Monkey Slug vs. Typical Moth Caterpillar

Feature Monkey Slug Typical Moth Caterpillar
Head Not visible Visible
Legs Prolegs with suckers Prolegs and true legs
Tentacles Long and fleshy Absent or short

Feeding Habits

Monkey Slugs are seen as pests by gardeners due to their feeding habits. They prefer to feed on tender leaves, which can lead to significant damage in gardens. Their diet consists of leaves from various plants, such as:

  • Beech
  • Oak
  • Hazel

Occasionally, they may also consume fungi and other plant material. It’s important to note that the preferred food sources vary between different slug caterpillars. In general, the behavior and diet of Monkey Slugs are influenced by factors like moisture and the availability of suitable plants.

To summarize the key points:

  • Monkey Slugs have prolegs with suckers for locomotion and cling onto leaves and plants.
  • They feed on tender leaves, making them a nuisance to gardeners.
  • Their diet varies between different species and is influenced by factors like moisture and plant availability.

Predators and Defense Mechanisms

Monkey Slug’s Natural Enemies

Monkey slugs, also known as hag moth caterpillars, face various natural enemies in their environment. Some of their predators include:

  • Snails: A type of gastropods that can prey on caterpillars like the monkey slug 1.
  • Parasites: Certain parasites may specifically target or infest monkey slug populations 2.

Protection Strategies

The monkey slug caterpillar has developed unique defense mechanisms to deter its predators and protect itself:

  • Setae: Monkey slugs have distinctive hair-like setae covering their body, which can cause irritation to sensitive skin. This fur-like appearance deters predators from feeding on them due to the potential discomfort it may cause 3.
  • Camouflage: They possess a natural ability to blend in with their surroundings. Resembling a small pile of dead leaves or a rock, the monkey slug can effectively hide from potential predators by mimicking elements in its environment 4.
Defense Mechanism Description Effectiveness
Setae Hair-like structures Deter predators
Camouflage Mimic natural elements Hide from predators

In conclusion, monkey slugs have developed effective defense mechanisms to protect themselves from their natural enemies, such as snails and parasites. By employing a combination of setae and camouflage, they manage to avoid predation and maintain their populations in the wild.

Human Impact and Interactions

Gardening Consequences

Mollusks like the monkey slug can cause damage to plants in gardens. They are known to feed on leaves, which may negatively affect plant growth. For example, hostas are a favorite of many gardeners, but they can also be attractive to monkey slugs.

One common impact on plants:

  • Damaged leaves

Preventing Slug Infestations

There are various methods and techniques that gardeners can use to prevent slug infestations and protect their plants.

Creating barriers:

  • Place copper tape around plant pots
  • Spread diatomaceous earth or crushed eggshells around plants

Traps and natural predators:

  • Beer-baited traps
  • Introduce beneficial predators such as birds and frogs

Slug-repelling plants:

  • Plant garlic, fennel, thyme, or rosemary to deter slugs

Pros and Cons of some prevention techniques:

Technique Pros Cons
Copper tape Environmentally friendly, reusable Expensive, less practical for large gardens
Beer-baited traps Effective, affordable Requires regular maintenance, may attract other pests
Beneficial predators Natural, sustainable May take time to establish, can be unpredictable

Remember to always keep pets away from any traps or substances used in slug prevention, as some can be harmful to animals.


  1. Snails in home gardens | UMN Extension
  2. USDA APHIS | Protecting Livestock from Predators
  3. The Caterpillar Lab
  4. Videographer’s Guide to Insects | Example.com

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 – Hag Moth Caterpillar


Strange Creature
My husband found this strange creature crawling on our truck under an oak tree. Is it some kind of larva camouflaged as a leaf? It was almost slug-like on its underside (but didn’t seem to be leaving a slimy trail) and had a very strong suction hold to the glass jar I had put it in. It was about 3/4″ in length. The “leaf” part appeared to be very soft/velvety. We live in SE Virginia. Can you help us identify this?

Dear Michelle,
Sometimes called the monkey slug, the full-grown hag moth (Phobetron pithecium) caterpillar is brown, 0.5 inch long, and has nine lateral lobes or processes with urticating (stinging) hairs. Some of these lobes protruding from the sides of the body are longer than others and are occasionally shed. Hag moths caterpillars are present in summer and fall. They produce one generation per year. Host plants include various forest trees and shrubs.
“Phobetron pithecium is called the Hag Moth because the dark brown larva has eight relatively long, fleshy, hairy appendages that cover the back, project from the sides and have a backward twist like locks of disheveled hair. They are, in fact, fleshy hooks covered with feathery, brown hairs among which are longer, black, stinging hairs. the cocoon is almost spherical and is defended by the hairy appendages that the larva in some way contrives to leave on the outside. These tufts give to the bullet-shaped cocoon a nondescript appearance and the stinging hairs afford a very perfect protection against birds and other vertebrates. The adults fly in midsummer. The female is brownish marked with yellow; the male is smaller.” according to Lutz.
Here is a great site with more information on stinging caterpillars.

Letter 2 – Brazilian Monkey Slug Caterpillar


What is this?
I found this insect in my garden, located in Brazil southeast (São Paulo, São Paulo), i have no ideia of what is it, I tried to understand this the hole day. It has 1,5cm-2,0cm, still alive, but don’t move frequently. the shape is what I think is more interesting. Can you answer what is it??? Thanks
Luiz Fernando R. de Sá

Hi Luiz,
This caterpillar bears a striking similarity to the Monkey Slug Caterpillar found in the Southern U.S. Though it might be a different genus, we believe it is still in the Slug Moth Family Limacodidae. Slug Moth Caterpillars often have stinging spines, so handle with caution.

Thanks for the anwser! I could discover what bug was! Here this bug is called “Lagarta-Aranha” something like “Spider Catterpillar” in English, real thanks! Have a nice day

Letter 3 – Hag Moth Caterpillar or Monkey Slug


slug that looks like a leaf
During a camping trip last Saturday one of the kids found an unusual creature. These pictures are of a slug type creature that was found in a wooded area near a lake about 40 miles north of Pittsburgh PA. From the side it looks like curled horns. From the top it appears to look like a brown leaf. From the bottom you can see a orange caterpillar type body. It could move the leaf looking appendages. Please help us identify this creature.

Hi Rick,
The Hag Moth Caterpillar is also known as a Monkey Slug.

Letter 4 – Monkey Slug


Just Add to Your Great Submissions
I always go to your site when I have a bug I don’t know (disturbingly, it happens a lot not because of lack of knowledge but because of our multitude of bugs!!). My son and I LOVE your site!!! We can view all the strange bugs that are cool and gross and creepy and cute. Anyway, thought you might want to add this shot of a Hag Moth we found in a bush in our front yard. I Identified it in part with your website’s help-Thanks. Luckily I did NOT pick it up as I had intended to do because I just learned they sting and it is not a nice thing especially in those prone to allergic reactions (me). Anyway-our family loves your site. Keep up the great work and I am sure eventually I will find something you haven’t already identified and will send it your way.
K. Ackles
Friendswood Texas

Hi K,
Your photograph is such an interesting angle on the Monkey Slug, another common name for the stinging Hag Moth Caterpillar.

Letter 5 – Monkey Slug


What on earth is this?
September 28, 2009
While moving, my friends found this on a cardboard box that had been sitting, undisturbed in a storage room for over a year. It reacted only slightly to being touched, but when a lighter was held a few inches away from, the pustule looking things started to swell and it lifted up a few of its legs (arms?). They’ve left it alone since, except for calling me to take some pictures. In a 24 hour period it’s moved about 4 inches across the top of the box, though rarely moves at all when we’ve been looking at it. We live in southcentral Oklahoma, and the weather has been very hot for months, so the closed off storage room it was in, was very warm, and moderately humid.
curious okie
south central Oklahoma

Monkey Slug
Monkey Slug

Dear curious okie,
This is a Monkey Slug, the caterpillar of the Hag Moth, Phobetron pithecium.  It is one of the Stinging Slug Caterpillars in the family Limacodidae, and it should be handled with caution.

Letter 6 – Monkey Slug


What kind of bug is this?
Location:  A Lake near Kingston, Ontario, Canada
August 16, 2010 10:17 pm
We saw this bug on a camping trip near Kingston, Ontario, Canada. What kind of bug is it?

Monkey Slug

This unusual caterpillar is a Monkey Slug, Phobetron pithecium, and caution should be exercised in handling it because it can sting.

Letter 7 – Monkey Slug


What is this? Some kind of Slug?
Location:  Knoxville TN
September 5, 2010 10:25 pm
Mr. Bugman, during a search for bugs for my 7th graders classification project, I came across this interesting creature. It was munching on the leaves along a tree line adjacent to my lawn. It moves around like some kind of slug, but it’s the wierdest thing I’ve ever seen.
Signature:  askeen

Monkey Slug

Dear askeen,
Though it is called a Monkey Slug, your creature is actually a caterpillar.  Handle it with care as it is capable of stinging.

Letter 8 – Monkey Slug


Leaf-type bug
Location:  Napanee, Ontario
September 18, 2010 10:09 pm
Found this on a maple tree outside our house. We live in Eastern Ontario.
Signature:  Curious about this bug

Monkey Slug

Dear Curious,
This is a Monkey Slug Caterpillar,
Phobetron pithecium, and in its adult form it is known as a Hag Moth.  BugGuide has this interesting description:  “Caterpillar is most frequently seen. Bizarre, brown, hairy creature that resembles some sort of aquatic creature more than a caterpillar. Three pairs of long arms and three pairs of short arms, which are ‘deciduous’ – often one or more is missing.”  Exercise caution when handling the Monkey Slug as it is one of the Stinging Caterpillars in the family Limacodidae.

Letter 9 – Monkey Slug


Location:  Orlando, Fl
October 13, 2010 3:22 pm
Dear Bugman, I was out by the lake taking pictures, when I spotted this little guy. I’ve lived in Fl all my life, where weird bugs are the norm. But I have never seen anything like it before. Could you please tell me what type of insect this is? Thanks, I appreciate your help!
Signature:  Sincerely, Karen V

Monkey Slug

Hi Karen,
This is a Monkey Slug Caterpillar, but it looks quite different from other Monkey Slugs on our website, and we believe that this is because it is an earlier instar.  We did find a matching image on BugGuide.

Letter 10 – Monkey Slug


Cephalopod like Door Creature
Location:  Richmond, Virginia, USA
October 20, 2010 7:55 am
On October 18 at about 8 pm I found this creature attached to the outside of the glass on my back door. Although I never saw it move after a 2 hour period it had changed position from the bottom right to about the middle left of the door window. It is slightly bigger than a 5-cent nickel.
After taking the pictures I put it in a small votive glass with a piece of cardboard, secured with rubber bands, on top. That left a less than 1/8 inch gap on one side of the glass jar which is much less than the width of the creature. I placed it outside my garage door at 11 pm and went to bed. I checked on it at 8:30 am the next morning and it was still in the same position in the jar. Checking again 3 hours later and it was gone apparently having slid through the 1/8 inch gap. I have not seen it since.
Signature:  Bob from Richmond

Monkey Slug

Hi Bob,
This interesting creature is the caterpillar of the Hag Moth and is called a Monkey Slug.  It should be handled with caution as it is a stinging caterpillar.

Letter 11 – Monkey Slug


Location: Colombia
January 8, 2011 6:01 pm
I found this strange ”bug” and was wondering what it is. My guess is a catapiller. I am in the Eastern Cordillera of Colombian Andes.
Scale in cm.
Signature: Scott Parks

Monkey Slug

Hi Scott,
This is a Monkey Slug,
Phobetron pithecium, and you are correct that it is a caterpillar.

Letter 12 – Monkey Slug


weird bug from Mo. i think its a catapiller of some sort?
Location: springfield, Missouri
August 9, 2011 7:52 pm
I found the strangest looking bug in Springfield mo. Today. It looks kina like a black fuzzy star fish but moves like a catapiller. Its belly looks like somekind of jelly substance that rolls. It can move and flip itself from any direction. HELP please!
Signature: fiesty4ever

Monkey Slug

Dear fiesty4ever,
The Monkey Slug is the caterpillar of the Hag Moth, and it is a Stinging Caterpillar that should be handled with caution, or better yet, not handled at all.

Letter 13 – Monkey Slug


Subject: unknown bug/caterpillar in vt
Location: monkton vermont USA
August 26, 2012 2:52 pm
We found this bug on our deck – we have other photos
Signature: Dylan Weaver

Monkey Slug

Hi Dylan,
You were astute to recognize this Monkey Slug as a caterpillar.  It is actually the caterpillar of the Hag Moth,
Phobetron pithecium.  The Monkey Slug is capable of stinging, so handle with caution.  We are amused that this Monkey Slug was photographed in the city of Monkton. 

Letter 14 – Monkey Slug


Subject: strange insect found
Location: Essex Jct, Vermont
September 3, 2012 12:54 pm
My son spotted a very odd looking insect crawling up a tree at our home in Vermont. It was orange in color and looked like the inside of a crab shell on the back but moved very much like a snail. It had a wormlike head and measured approximately one inch long and was soft and had no shell. What is this thing?
Signature: Steven and Connor

Monkey Slug

Hi Steven and Conner,
This creature, which is commonly called a Monkey Slug, is the caterpillar of the Hag Moth.  Handle with caution as they are capable of stinging.

Letter 15 – Monkey Slug


Subject: Crazy caterpillar type thing
Location: Southeastern PA
August 5, 2013 3:43 pm
This fell out of my weeping Chinese elm in southeastern PA…. Yikes! What is it?
Signature: C Mchugh

Monkey Slug
Monkey Slug

Dear C Mchugh,
We were out of the office when you submitted your request and we are just attempting to catch up on a small fraction of our unanswered mail.  This is a Monkey Slug,
Phobetron pithecium, a Hag Moth caterpillar in the family Limacodidae.  Handle with care.  Monkey Slugs sting.

Letter 16 – Monkey Slug


Subject: What’s this leaf like bug?
Location: Steubenville, ohio
September 2, 2014 6:58 pm
I live in eastern Ohio and found this on a friends car. It has a worm like belly but looks like a fluffy leaf.. Never seen anything like this before!
Signature: Geno

Monkey Slug
Monkey Slug

Hi Geno,
This is a Monkey Slug, the caterpillar of a Hag Moth.  Handle with care.  Monkey Slugs can give a nasty sting.

Letter 17 – Monkey Slug


Subject: What is this?
Location: Martinsburg, WV
September 27, 2014 4:48 pm
Caterpillar looking underneath but like a leaf or something on top? It was on my car window 9/27/14 in The a eastern panhandle of WV
Signature: Jen A.

Monkey Slug
Monkey Slug

Dear Jen A.,
This is a Monkey Slug, the caterpillar of a Hag Moth,
Phobetron pithecium.  Monkey Slugs should be handled with caution, because according to BugGuide:  “Caution, This is a stinging caterpillar.”

Monkey Slug
Monkey Slug

Letter 18 – Monkey Slug


Subject: Mustachio
Location: Downingtown PA
August 21, 2015 8:00 pm
We saw this bug today, August 21, in Downingtown Pennsylvania. It was creeping along a leaf like it had lots of tiny centipede-like legs on the underside.
Signature: Amanda

Monkey Slug
Monkey Slug

Hi Amanda,
Believe it or not, this is actually a caterpillar commonly called a Monkey Slug.  Handle with caution, or not at all, as the Monkey Slug can sting.

Letter 19 – Monkey Slug


Subject: Seems to have horns but slides like a snail…
Location: Columbus, Georgia, United States
January 22, 2016 6:07 pm
Coworker found this on her truck, last summer…maybe end of July. We are in Columbus, Georgia, United States.
She said this bug was in the process of forming a web; it was leaving some sort of sticky substance. It ‘slid’ like a slug but moved sideways, it had no legs. It looks as if it has some sort of horns above what she thinks are the eyes. She saw a smaller one the next day but never saw anymore and hasn’t been able to find out what it is online or in any book she’s researched.
Signature: Monica Edmonds

Monkey Slug
Monkey Slug

Dear Monica,
This is a Monkey Slug, one of the Stinging Slug Caterpillars in the family Limacodidae.  It appears to be missing several of its “arms” and it is described on BugGuide as being:  “Bizarre, brown, hairy creature that resembles some sort of aquatic creature more than a caterpillar. Three pairs of long arms and three pairs of short arms, which are “deciduous” – often one or more is missing.”  It is capable of stinging and it should be handled with caution.

Letter 20 – Monkey Slug


Subject: leaf looking with no legs
Location: Auburn, NY
August 15, 2016 6:07 pm
I live in Auburn, NY and this was on the table underneath a black walnut tree. We thought it was a shriveled leaf, but it was soft and moved.. Looking closer, it has a soft whitish underbelly and no visible legs, just star like legs of the leaf looking back.. But they don’t move. Very slow moving, What is it?
Signature: Pat P

Monkey Slug
Monkey Slug

Dear Pat P,
The Monkey Slug is the caterpillar of the Hag Moth.  Handle the Monkey Slug with caution.  It is a stinging caterpillar.

Thanks so much. We were all surprised by it and did not touch. Are they a nuisance moth  should they not be killed ?
Thanks again.
Have a truly wonderful day!

This is a native species, not a pest species.  We do not support killing either the Monkey Slug caterpillar of adult Hag Moth.

Thanks again. I was careful to let it go in the brush. I don’t kill critters unless they are a danger. Good to know they aren’t harmful. It was very interesting to watch.
Have a truly wonderful day!

Letter 21 – Monkey Slug


Subject: What could this alien be?
Location: Atlanta, Georgia
September 11, 2016 9:10 am
This attached itself to my friends car and rode the whole way home. Moved at the pace of a snail.
Signature: From, Zan

Monkey Slug
Monkey Slug

Dear Zan,
This is a Stinging Slug Caterpillar commonly called a Monkey Slug.  Monkey Slugs and other Stinging Slug Caterpillars should be handled with extreme caution because contact may result in a painful sting, and possibly an allergic reaction.

Letter 22 – Monkey Slug


Subject: What is this bug?
Location: Ashboro, North Carolina
July 12, 2017 7:25 am
We saw this bug on July 11th at the North Carolina Zoological Park in Ashboro, North Carolina. My 22 year old daughter took a video and showed it to an employee who said she had never seen anything like it and that it moved like a caterpillar
Signature: LeeAnne

Monkey Slug

Dear LeeAnne,
Though it does not look like other caterpillars, this Monkey Slug really is a caterpillar.  Handle with caution though, the Monkey Slug is capable of stinging.

Letter 23 – Monkey Slug


Subject: Help identify
Location: Northern Va
July 21, 2017 11:48 am
Found on car
Looks like a leaf, was crawling
Can find no info on any bug search site
Signature: Wendy

Monkey Slug

Dear Wendy,
Though it is atypical looking, the Monkey Slug is actually a caterpillar.  Handle with caution.  Monkey Slugs can sting.

Letter 24 – Monkey Slug


Subject: Weird insect
Location: Polk County, Texas
August 17, 2017 3:15 pm
Piney Woods area of Texas harbors lots of strange creatures. But this is the first time I’ve ever seen anything like this! What in the heck IS it?
Signature: MaryB

Monkey Slug

Dear MaryB,
This Caterpillar is commonly called a Monkey Slug, but handle with caution as they are capable of stinging.

Thank you so much!  I see lots of strange critters out here in the boonies and this thing is now rated #1 on my weird list.
No touchie, just lookie. 😉

Letter 25 – Monkey Slug


Subject:  Big hairy orange bug
Geographic location of the bug:  Central Ohio, USA
Date: 12/03/2017
Time: 09:09 PM EDT
Dear Bugman,
We saw this bug while camping in central Ohio several years ago, and can’t find anything like it and are wondering what it is. It crawled along quite like a snail, but left no trail and had no shell. When it moved the leaf-like formations undulated in a wave-like motion.
How you want your letter signed:  Mary Skrenta

Monkey Slug

Dear Mary,
This is a Caterpillar that is commonly called a Monkey Slug.  They should be handled with caution as they are capable of stinging.

Letter 26 – Monkey Slug


Subject:  Strangest bug I’ve ever seen
Geographic location of the bug:  Northeast Pennsylvania
Date: 08/22/2018
Time: 04:44 PM EDT
Your letter to the bugman:  Found this crawling on my window. It moves like a slug. When you watch it the whole body ripples to make it move.
How you want your letter signed:  Megan

Monkey Slug

Dear Megan,
This unusual caterpillar is commonly called a Monkey Slug.  Handle with caution as they are capable of stinging.  According to BugGuide:  “Caterpillar is most frequently seen. Bizarre, brown, hairy creature that resembles some sort of aquatic creature more than a caterpillar. Three pairs of long arms and three pairs of short arms, which are ‘deciduous’ – often one or more is missing.”

Letter 27 – Monkey Slug


Subject:  Strange furry purple caterpillar
Geographic location of the bug:  Florida panhandle
Date: 10/23/2018
Time: 05:53 PM EDT
Your letter to the bugman:  Hey bug man this little guy fell out of a tree in my windshield on my way home today  I’m semi new to Florida and know there are lots of crazy bugs here. Never seen one of these tho. It is about an inch long dark purple with some reddish orange on the underbelly. Did a reverse image search to try to find the species. No luck. Made it all the way home and took him off the car and realeased him in the grass. Thanks for any help!
How you want your letter signed:  Jordon

Monkey Slug

Dear Jordon,
You should be commended on even recognizing that the Monkey Slug is a caterpillar.  Handle with caution.  Monkey Slugs can sting.

Letter 28 – Monkey Slug


Subject:  Can’t narrow it down..
Geographic location of the bug:  Eastern Panhandle, West Virginia
Date: 08/28/2021
Time: 08:09 PM EDT
Your letter to the bugman:  I saw this hanging out on my car and right away thought it might be a bug/insect.  It’s interesting because it’s camouflaged and would hide very well on trees in my yard, but it was on my silver car and stood out like a sore thumb.  How it ended up on my car, I have no idea unless it fell from above from the tree.  Currently it’s August 2021 and weather is 90 degrees and humid.  When it moved, the many white feet moved from back to front and slow.  I saw it’s face on the underside, not out front.  Anyhow… I was thinking along the lines of a millipede, or isopod but can’t find any pictures close enough to id.
How you want your letter signed:  Camouflaged Something

Monkey Slug

Dear CS,
Very few people realize they are looking at a Caterpillar when they encounter a Monkey Slug.  Handle with caution as the Monkey Slug can sting.

Letter 29 – Monkey Slug


Subject:  What is this bug?
Geographic location of the bug:  Cincinnati ohio
Date: 09/27/2021
Time: 07:48 PM EDT
Your letter to the bugman:  This bug fell from a tree at winton woods park onto my car.
How you want your letter signed:  From Pamela Cupp

Monkey Slug

Dear Pamela,
Upon reading your letter, Daniel immediately suspected correctly that you encountered a Monkey Slug.  These stinging caterpillars frequently fall from trees onto cars.

Thank you.  I’d never seen anything like it.  Appreciate your reply.
Take care,

Letter 30 – Monkey Slug and Homepage issue


Subject: An observation of the Home Page
Location: No. Va
September 4, 2012 1:50 pm
Greetings – Have just happened onto your page in process of trying to identify what turned out to be a Hag Moth larvae which dropped onto my hand today. Will doubtless be back – very useful sight – especially for nat’l science junkies.
I will attach a screen shot of the top left area of your home page which is somehow missing some of the text to tell us what we need to click on to reach the ’Ask WTB’ and ’Bug Love’ linked pages. (Have worked on websites – not a techie, but writer/editor and pay attention to such stuff.) Thought I’d share the info in case you hadn’t seen it. Thanks…
Signature: Sue Hodapp

Monkey Slug

Hi Sue,
We are happy you were able to identify your Hag Moth Caterpillar, commonly called a Monkey Slug, thanks to our website.  As a side note, we accidentally hit the “t” instead of the “g” when naming the Monkey Slug and we needed to correct that error prior to posting since we try our best to maintain a G rated website.  Thanks for bringing the homepage problem to our attention.  We will copy our crack webmaster on this matter to see if he can get to the root of the matter.  We just checked it out on our Safari and Firefox browsers and it is fine.

WTB? Screenshot with technical problem

Letter 31 – Monkey Slug from Brazil is Lagarta-Aranha


Subject: weird bug
Location: Marechal Cândido Rondon, Paraná state, Brazil
January 2, 2016 9:21 am
Hi there,
I live in Southern Brazil and I found a very strange bug on a cherry tree, during the summer (about 90F), in the morning. I am very curious because I have never seen something like it. It moves slowly (well, at least after I kicked him) and it is very hairy. Here are some pictures.
Thank you!
Signature: Sincerly

Monkey Slug
Monkey Slug

This looks similar enough to a North American Monkey Slug that we believe your individual is also a member of the genus Phobetron.  When we previously posted a similar image from Brazil, we learned that a common local name is:  “‘Lagarta-Aranha’ something like ‘Spider Catterpillar’ in English.”

Monkey Slug
Monkey Slug

Fantastic! I was really puzzled about that bug!
Thank you very much!

Letter 32 – Monkey Slug Caterpillar


I found your web page while trying to identify a hummingbird clearwing moth that I took a picture of yesterday and decided you might can help me identify the attached picture. This bug was crawling on our car and we let it crawl onto the graph paper in order to take its picture. Do you know what this creature is? Thanks a lot for you help.
Julie and Jim

Hi Julie and Jim,
What an artful photograph of a Monkey Slug Caterpillar or Hag Moth Larva, Phobetron pithecium. This is a stinging caterpillar.

Letter 33 – Monkey Slug Caterpillar


Monkey Slug Caterpillar?
Greetings Lisa Anne and Daniel,
I just this evening found your website – it’s fantastic and I love it! A couple of years ago, we found a part of one of these caterpillars on my husband’s car windshield and thought we had entered the Twilight Zone! We live in New Hampshire (the Mount Washington Valley) and recently found several in a small maple tree. From research I have been able to do, I think they are of the family Limacodidae and a relative of Phobetron hipparchia – maybe Phobetron pithecium? Although I handled them before I knew anything about them (not always a wise move and fortunately I suffered no ill effects), you can see in the second picture that they have stinging spines. They certainly are beautiful! long — and in this particular photo, she is very near to being lifesize. Do you
know who she is exactly? Thanks for enjoying them with me.
Judi Paul

Hi Judi,
Due to time constraints, we are editing your letter and only posting the image of the Monkey Slug Caterpillar, a stunning image.

Letter 34 – Monkey Slug Caterpillar


Bug of interest
Found your web site while looking to identify the attached “bug”. My wife and I were on vacation Sept. 15th in the Blue Ridge Parkway and found this little fellow on the side of the car while parked at a picnic area located at about 3600 feet elevation. We photographed him/her, put him on a near by berry tree and moved on up the parkway. At another stop we found a second one stuck to the side of the car. We were traveling through an area of the parkway on which the trees hang directly over the roadway. Watched it for a while and after deciding that it wasn’t going to move on its own, we moved it to safer location and we moved on. Didn’t see anymore of these fellows at the lower elevations. Having looked over your web site, I thought you might like a copy of the “bug”. Thanks for being out there… our young people need to stay in touch with nature more.
Terry Willis

Hi Terry,
This is a Monkey Slug Caterpillar, and you are lucky you did not get stung as they have stinging spines. We often get reports that people encounter them when they drop onto their cars.

Letter 35 – Monkey Slug Caterpillar


pink monkey slug in Pa.
Dear Daniel-
As I was waiting to get my kindergartner off the bus, I spied
this weird pink leafy thing on my mailbox. Imagine my surprise
when it moved!! I raced to get my camera and snapped a few
pictures. I didn’t want to touch it because I was afraid of
it stinging. Then I gently pried it up- this thing is sticky!-
to get a look at the underside. Very cool. I found the image
already on your site, but mine is a nice shade of pink. The
mailbox is under a large oak tree, which fits the information
I found on it. Enjoy!
Lee Weber
Nottingham, Pa.

Hi again Lee,
You were wise to not carelessly handle the Monkey Slug Caterpillar,
as it is one of the stinging caterpillars. This unusual caterpillar
is one of the most un-insectlike insects we can think of.

Letter 36 – Monkey Slug Caterpillar


strange little creature, moves like slug, orange color, appears to looks kind of fuzzy
September 4, 2009
While outside earlier I had bent down to pick something up, and out of the corner of my eye. I saw something fall. I looked over and it appeared as if a bloom had fallen off of an Indian Jewelweed…until I saw it moving! It had landed on top of a little stone, so my hubby picked it up (while it was on the stone) so I could get a couple of pictures of it. If anyone has any idea what this is, I’d really like to know. As I mentioned in the subject line, it is an orage color, and when looking at it in the pics, it appears to look ‘fuzzy’ ~ it’s movement is much like that of a slug because it seems to ‘suction’ to things and crawl across. if by chance you know what this is, how could we care for it here for a few days? My daughter is in the 11th grade and has just started her ‘Zoology’ class ~ she’d love to take it in to show her teacher! (It’s Labor Day weeked, so school won’t be in session for three days.) We don’t want to harm it in anyway…it is so very interesting. Any help is much appreciated! Thank you.
Barbara M.
Fayette County, WV

Monkey Slug Caterpillar
Monkey Slug Caterpillar

Dear Barbara,
Handle this Monkey Slug Caterpillar, Phobetron pithecium,
with care.  It is not an aggressive species, but careless handling might cause skin contact with the stinging hairs.  The Monkey Slug Caterpillar is the larval form of the Hag Moth and you may read more on BugGuide which indicates:  “Larvae feed on broad-leaved trees and shrubs, including oaks, cherries.

Well, who knew? Not I! Thank you so much for answering my question, I had never seen anything quite like that before! Thanks, also, for the link you sent and informing that it stings! Have a wonderful weekend!

Letter 37 – Monkey Slug Caterpillar: It Stings!!!


Bug ID
My closeup makes it look like it has hair, looking directly at it though it looks like a leaf. It dropped on our windshield while parked under some trees. It has a sticky sucking bottom. We are in Ohio and we drove 15 miles home while it stuck to the windshield. Thanks for any input, I can’t find anything on the internet.

This is a stinging Monkey Slug Caterpillar, and your photo of it is awesome.

Letter 38 – Monkey Slug from Costa Rica


Subject:  octopus looking bug
Geographic location of the bug:  Arenal, Costa Rica
Date: 03/28/2018
Time: 07:02 PM EDT
Your letter to the bugman:  I found the weirdest insect in Costa Rica Arenal at a Hotel Lomas Del Volcan
it was near the pool on a palm leaf. When we first saw it we thought it was dead leaf on the palm  tree. I shook the palm leaf and it fell to the ground that is when I saw it was a living thing.  One of the appendages came off. I think this might be a defense I am not sure.  I picked it up and we got one pic of the underside looked like some type of slug.  I then turned it back upright and put it back on the palm leaf. It looked like it puffed up and was going to metamorph into something else. In the morning I checked on it and it had moved again from the underside of the leaf to the top of the palm leave. so it looked like it formed a protection and then moved when it was ready. Very strange looking forward to knowing if you have ever seen anything like this before.
How you want your letter signed:  Terri Martin

Monkey Slug

Dear Terri,
This is the caterpillar of a moth in the genus
Phobetron, and in North America, the species Phobetron pithecium, the Hag Moth has a similar looking caterpillar commonly called a Monkey Slug, but caution should be exercised when handling the unusual caterpillar as it is capable of stinging.  Researchgate has a scholarly article entitled Twenty-Five new species of Costa Rican Limacodidae that lists six newly discovered species in the Phobetron complex including Phobetron guzmanae and Alex Hyde PHotography has an image of an adult Phobetron hipparchia from Costa Rica.  If Alamy is correct, the Monkey Slug ranges as far south as Costa Rica, but we would not rule out that your caterpillar might be a member of a different species in the genus or possibly the genus complex mentioned earlier. 

Letter 39 – Monkey Slug from Belize


What’s Yellow and Furry and Just Plain Strange?
Location: Central America (Belize or Guatemala)
October 13, 2011 1:47 pm
My daughter and I saw this in Belize or Guatemala (can’t remember what part of the trip) and are stumped. Totally and completely.
Signature: Shoshana

Monkey Slug from Belize

Hi Shoshana,
This caterpillar looks so much like the stinging Monkey Slug from North America,
Phobetron pithecium (see BugGuide), that we believe it is either the same species, a subspecies, or a closely related species in the same genus.

Letter 40 – Monkey Slug from Panama


Hag Moth Caterpillar?
My name is Lidia, (I don’t speak english so much) I saw your page ‘What’s that bug’ and I like it, I saw an stranger bug in a tree in front of my house two weeks ago (I live in Panamá) and I was surprised and then I started to search in the web and I found your page, and I now I think that this caterpillar is a Hag Moth Caterpillar or Monkey slug. This is true? Sorry for the bad quality of the pictures. Thanks.

Hi Lidia,
While we cannot guarantee that your caterpillar is the same species as the North American Monkey Slug, Phobetron pithecium, the maps on BugGuide as well as our own letters indicate they are common in Texas. If they are in Texas, chances are quite good they are in Mexico. Since plants and animals tend to ignore international borders, chances are also good they may be found in Central America including Panama. If your specimen is not the same species, Phobetron pithecium, it is definitely in the same genus. It is therefore valid to call your caterpillar a Monkey Slug.

Letter 41 – Monkey Slug is center of attention


Need help IDing bug pic from Wisconsin
What a delightful site! Have three boys 7 and under and we learn a great deal from your site. Attached is a creature that fascinated myself and extended family in August ’07. Taken on property in SE Wisconsin with many old growth deciduous trees. My uncle has lived on the property 35 years and never saw such a specimen before. Could you help us learn a bit about it? Many thanks,

Hi Kristin,
We love this photograph so much. This is the Caterpillar of a Hag Moth, known as a Monkey Slug. Careful, since it is a stinging caterpillar.

Letter 42 – Monkey Slug relative from Venezuela may be Phobetron hipparchia


Subject: what’s that bug?
Location: Caracas, Venezuela
December 28, 2013 1:21 pm
Just saw this thing in my yard, it didn’t move, but it seems to be eating that leaf. Do you know what it is?
Signature: ukimalefu

Monkey Slug from Venezuela
Monkey Slug from Venezuela

Dear ukimalefu,
Your caterpillar bears such a strong resemblance to the Monkey Slug, the caterpillar of the Hag Moth,
Phobetron pithecium, that we believe it must be a close relative in the same genus, or perhaps even the same species.  See BugGuide for a matching photo, and see BugGuide‘s information page for things that might apply to a South American relative, including the fact that Monkey Slugs are stinging caterpillars and they should be handled with extreme caution.  FlickR has a photo from Venezuela that is identified as Phobetron hipparchia.

Yes, it definitely looks like the monkey slug. Thanks!

Letter 43 – Monkey Slug from Yucatan


Subject: Help
Location: Yucatan Peninsula
December 18, 2016 7:32 am
A friend of mine sent this pict to me. She is vacationing on the Yucatan peninsula. Can you identify this?
Signature: John

Monkey Slug
Monkey Slug

Dear John,
This is either a North American Stinging Slug Caterpillar commonly called a Monkey Slug,
Phobetron pithecium, or a close relative in the same genus.  The adult moth is known as a Hag Moth.

Letter 44 – Monkey Slugs


Subject: What’s this bugs name
Location: Arena, Wisconsin
August 2, 2016 11:53 am
I found this bugs all over my apple tree and I’ve never seen anything like this.
Signature: Kary

Monkey Slugs
Monkey Slugs

Dear Kary,
These Caterpillars are commonly called Monkey Slugs and they should be handled with caution as they are capable of delivering a painful sting.


  • 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.

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  • 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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14 Comments. Leave new

  • I’m really curious to see what these things look like when they pupate. I can’t imagine a nice smooth round pupa when the larva has all of those weird tentacle-like protrusions. Can they move those “arms” by the way?

  • Phobetron sp., Monkey Slug Caterpillar. The most common one in Brazil would be Phobetron hipparchia, which is very variable.

  • Hi Daniel
    Regarding your homepage glitch, I see the same thing, but I had always put it down to it being a peculiarity of my netbook computer with its very small screen. I am using Windows 7 Starter Edition, with Internet Explorer 9. My husband’s laptop has the same issue, his is Windows 7 Home Professional w/ IE9. The glitch has never bothered me, but I’ve been using your site for a long time and know where your submission and bug links buttons are. I imagine it could be a problem for newcomers, though.

  • Daniel, there are some clues that states that Phobetron stings are a legend.
    I have a report of a woman handling it ith no effects and I found a discussion on Bugguide:
    Phobetron also appears in some of our literature as dangerous, do you have any case or know about it?

  • Daniel, there are some clues that states that Phobetron stings are a legend.
    I have a report of a woman handling it ith no effects and I found a discussion on Bugguide:
    Phobetron also appears in some of our literature as dangerous, do you have any case or know about it?

    • Hi Cesar,
      Thanks for pointing out this possibility. I cannot recall getting any actual reports of people being stung. Perhaps the reputation of the Monkey Slug originates because of other stinging members in the family.

  • i live in Paris, KY and came home today and found one on my front porch. Which lead me to this website,

  • Monica Edmonds
    January 23, 2016 3:57 pm

    Thanks so much for the info. This bug was so freaky looking, I had to know what it is. I never would’ve guessed it stings, great to know.

  • What Ecuadorian spider spits a brown liquid (I assume a mild acid) when threatened? The spider in question looked like a large huntsman, maybe 4-4.5 inches across (including legs). Very hairy. As I approached to pick it up it backed against the wall and raised then waved its front four arms at me and arched its cephalothorax making it difficult to pin it down to pick up like you would a tarantula. When I picked it up, it squirted a brown liquid on my hand, but otherwise was not aggressive.

  • I found a slug that looks like a monkey or mongo slug. It was on my head and now it itches
    Like crazy. Do they lay eggs?
    I drove a convertible to Charlottesville , va and parked under trees. Must have picked it up there

  • I found a slug that looks like a monkey or mongo slug. It was on my head and now it itches
    Like crazy. Do they lay eggs?
    I drove a convertible to Charlottesville , va and parked under trees. Must have picked it up there


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