Are Inchworms Caterpillars? Unraveling the Mystery

Inchworms, also known as cankerworms, are fascinating little creatures that can be found in many gardens and wooded areas.

These small, green, or brown insects are often seen inching their way across leaves, branches, and even pavements. But what exactly are inchworms? Are they caterpillars?

The answer is yes, inchworms are indeed a type of caterpillar. They belong to the family Geometridae, which includes over 1,400 species in North America alone.

Are Inchworms Caterpillars
Inchworm on Curry Plant

Inchworms are the larvae of moths in this family, and they’re known for their distinct way of moving.

They grip onto surfaces with the back set of their legs, and then pull their front half towards that point, resulting in a looping motion that resembles an inch being measured.

What makes them unique compared to other types of caterpillars?

  • A unique way of moving: Inchworms move by inching and looping their body, unlike traditional caterpillar crawling.
  • Wide variety of species: Over 1,400 inchworm species are present in North America.
  • Moth larvae: Inchworms are the larval stage of moths in the Geometridae family.

One such example of an inchworm species is the spring cankerworm, which feeds on the foliage of a variety of trees.

These larvae appear in spring, often coinciding with the opening of elm tree buds, and feed for about four weeks before reaching their full-grown length of approximately one inch.

Pink Inchworm

Are Inchworms Caterpillars? Understanding Inchworms and Caterpillars

Definition and Classification

Inchworms and caterpillars both belong to the larval stage of certain moths and butterflies. Inchworms, also known as:

  • Loopers
  • Cankerworms
  • Spanworms

Family Geometridae

Family Geometridae includes over 26,000 species of moths around the world. Inchworms, the larvae of these moths, have some distinctive features:

  • Elongated, thin bodies
  • Three pairs of legs at the front and two pairs of prolegs at the back
  • Distinct “looping” motion during movement

Here’s a comparison between inchworms and other caterpillars:

FeatureInchwormsOther Caterpillars
Legs3 pairs of legs and 2 pairs of prolegs at the backA varied number of prolegs and legs
MotionLooping motionCrawling or walking
Feeding habitsFeed on deciduous trees and shrubsVaried diet depending on species

Characteristics of Inchworms

Physical Appearance and Size

Inchworms typically have fewer legs than other caterpillars, with two or three pairs of legs towards their head and one or two pairs of legs, called prolegs, at the rear end.

The size of inchworms varies, but most species are around one-inch long.

Color Variation

  • Some inchworms are green, helping them blend in with leaves.
  • Others may be gray, brown, or black, allowing them to camouflage on tree bark or stems.

Locomotion and Movement

Inchworms move with a distinctive “looping” motion. This unique movement is due to their limited number of legs.

They stretch out their front end, grip the surface with their front legs, then pull their rear end up, forming a loop. This motion can be quite fascinating to observe.

Diet and Feeding Habits

Here’s a summary of their diet and feeding habits:

  • Inchworms feed on a variety of plants, both ornamental and native.
  • Some species feed specifically on conifers, while others prefer deciduous trees and shrubs.
  • They cause damage to plants by consuming leaves, sometimes resulting in defoliation.

Comparison of Inchworms and Other Common Caterpillars

FeatureInchwormsOther Caterpillars
LegsFewer legsMore legs
MovementDistinctive looping motionRegular crawling motion
DietPlant leavesPlant leaves or flowers
Damage to plantsDefoliationVaries depending on species

Life Cycle and Reproduction

Egg to Larva

Inchworms are the larvae of certain moth species and undergo a typical metamorphosis. They begin life as eggs laid by their moth parents on various deciduous trees.

  • Female moth crawls upward into trees
  • Deposits eggs in patches, compact masses, or loose clusters

For example, cankerworms are a type of inchworm, and their eggs hatch toward the end of May.

Larval Stage

The larval stage is characterized by inchworms’ distinctive “looping” motion. As caterpillars, they are also known as loopers or spanworms.

  • Primarily feed on deciduous tree leaves
  • Defoliate trees during outbreaks

Some common inchworm species include the cankerworm, fall cankerworm, and spring cankerworm.

Pupa to Adult

Inchworms transform into pupae before becoming adult moths. This process varies from species to species.

StageTypical Duration
EggVaries
LarvaVaries
PupaVaries
Adult MothVaries

Once they become adult moths, the cycle continues with the female moth laying eggs on deciduous trees.

Unknown Spanworm

Distribution and Habitat

Range and Distribution

Inchworms, which are the larval stage of geometer moths, can be found across the globe. They have a wide distribution, with nearly 23,000 species in the family Geometridae. Some common regions where they thrive include:

  • United States
  • Europe
  • Asia
  • Australia

Habitat Preferences

Inchworms can inhabit a diverse range of environments, such as:

  • Forests
  • Gardens
  • Grasslands
  • Urban areas

Their preferred habitats often contain an abundant food source, which mainly consists of leaves from various plants. Additionally, they can reside at different altitudes, from sea level to mountainous regions.

Comparison of Inchworms and Other Lepidoptera Larvae

Feature/CharacteristicInchwormsCaterpillars of Butterflies
FamilyGeometridaePapilionidae, Pieridae, etc
AppearanceLooping movementCrawl using prolegs
DietPlant leavesPlant leaves/specific host plants
Number of prolegs2 pairs3 to 5 pairs
PupationForm pupaeForm pupae/construct chrysalis

Pros and cons of inchworms in gardens:

Pros:

  • Natural pest control for some plant species
  • Food source for birds and other wildlife

Cons:

  • Potential to defoliate plants, especially in large numbers

Relationship with Humans

Inchworms as Pests

Inchworms are the caterpillar stage of certain moths. They feed on the leaves of various plants and can become pests when they infest in large numbers. They cause damage by defoliating trees, for example:

  • Apple trees
  • Oak trees
  • Elm trees

Infestation signs:

  • Chewed leaves
  • Leaf loss
  • Droppings on surfaces below the trees

Predators of Inchworms

Inchworms are an energy source for many predators, including:

  • Birds
  • Small mammals
  • Predatory insects (e.g., ladybugs, lacewing larvae)

These natural enemies help control the inchworm population and maintain balance within the ecosystem.

Control and Management

In order to mitigate inchworm damage, a combination of strategies can be employed.

Biological Control: Encouraging natural predators by providing habitats such as birdhouses, insect hotels, or planting flowers that attract ladybugs.

Physical Removal: Regularly check plants for infestation and remove inchworms or their eggs by hand when detected.

Chemical Control: Applying insecticides selectively, such as Bacillus thuringiensis (Bt), which specifically targets caterpillars and minimizes harm to other organisms.

MethodProsCons
BiologicalEnvironmentally friendlyMay not eliminate all infestations
Physical RemovalNon-toxic, no chemicals involvedLabor-intensive
Chemical ControlEffective in reducing infestationsHarmful to non-target organisms

Inchworms

Conclusion

In summary, inchworms are a group of caterpillars within the Geometridae family, having evolved millions of years ago.

They possess unique features and play a role in ecosystem dynamics. However, they can also be pests to crops and trees.

They are found in various habitats, often in gardens and forests.

With their distinctive locomotion, diverse color variations, and their capability to cause damage to plants, they are an interesting and unique subset of caterpillars.

If you want to protect your plants and crops from these insects, use the tips and tricks provided in the article to keep these insects at bay.

Footnotes

  1. https://entomology.ca.uky.edu/ef401 2

  2. https://hortsense.cahnrs.wsu.edu/fact-sheet/common-insects-and-mites-inchworms/

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 – Eighth Recipient of the Nasty Reader Award: Pink Inchworm

Ed. Note:  A mere ten days after making this post, it quickly rose to the fifth “most liked” posting on our site.

Ed. Note:  We haven’t been awarded a Nasty Reader Award in quite some time since most folks who write to us are polite and quite understanding that our small staff is unable to respond to every question we receive. 

This morning we happened upon this flurry of emails from Alexis Crowell, that came within three hours of one another.  Seems Alexis is demanding instant gratification and furthermore, (S)he has deplorable grammar. 

Additionally, the U.S.A. is a very broad location when it comes to trying to determine the identity of many insects that have a very localized range.  Further research into the matter revealed that Alexis did not even take the photographs, but rather pilfered them from other websites. 

With that said, we are unable to even respond to this rude query with any accuracy. 

It also appears that despite the poor grammar and spelling, Alexis has referred to our staff with a derogatory sexual orientation slur in the final correspondence that occurred a scant two hours and 45 minutes after the initial email. 

Seems Alexis is not only rude but a person who demands instant gratification.  For all of the above reasons, we are pleased to award Alexis Crowell of the U.S.A. as our latest Nasty Reader Award recipient.

Subject: are they rare?
Location: U.S.A
August 14, 2012, 3:08 pm
dear Bugman, is the pink inchworm rare or is it not that rare. Are there not that many inchworms?
Signature: sincerely, Alexis Crowell

Ed Note:  Our immediate automated response
Sent: Tuesday, August 14, 2012, 3:08 PM
Subject: Identification Request: are they rare?
Thank you for submitting your identification request.
Please understand that we have a very small staff that does this as a labor of love. We cannot answer all submissions (not by a long shot). But we’ll do the best we can!

Alexis Crowell alexisleecrowell@yahoo.com
3:19 PM (18 hours ago)
dear bugman it is ok
you can’t just try we are really curious about this unknown bug.

Alexis Crowell alexisleecrowell@yahoo.com
5:10 PM (17 hours ago)
JUST ANSWER US PLEASE I AM CRYING RIGHT NOW AND I HAVE BEEN STARING AT THE COMPUTER!

Alexis Crowell alexisleecrowell@yahoo.com
5:53 PM (16 hours ago)
texts back faget

Pink Inchworm from dailypress.com

Alexis,
Our online submission form clearly states:  “By submitting an identification request and/or photo(s), you give WhatsThatBug.com permission to use your words and image(s) on their website and other WhatsThatBug.com publications.

Also, you swear that you either took the photo(s) yourself or have explicit permission from the photographer or copyright holder to use the image.” 

Both of the images you have submitted have been pilfered from other internet websites, most likely without permission which is a copyright violation. 

One image came from http://www.dailypress2.com/photopost/showphoto.php?photo=111815 and the other is a photo credited to Dave Green posted on http://daylight44.net/pinkinch.html which can be accessed by clicking the Photo of Pink Inchworm link. 

You have plagiarized the work of other photographers and submitted them using our online form which specifically indicates that you have taken the photos or you have permission to use the photos. 

Additionally, your flurry of emails in rapid succession ending in an incorrectly spelled sexual orientation slur has gained you the distinction of being awarded the Nasty Reader Award as well as a feature on our scrolling announcement bar. 

The Nasty Reader Award is a distinction we have not had the pleasure to award in over two and a half years, which is an indication that most people who write to us are polite and well-mannered. 

Please search elsewhere for information on Pink Inchworms.  Responding to you is not worth any more of our time which is quite precious to us.

Pink Inchworm from Daylight 44

Ed. Note:  excerpt from another response.
… so sorry you had to award your Nasty Reader award … what a jerk!
the rest of us really love what you are doing and appreciate your time, efforts, and your willingness to share your knowledge.
Donna

Letter 2 – Camouflaged Looper

Subject: brown leaf-covered caterpillar
Location: Bradenton, Fl
July 4, 2014, 5:07 am
I found this, what looks like a caterpillar covered with brown leaf covering, in my Florida yard.
Signature: Thuy

Camouflaged Looper
Camouflaged Looper

Dear Thuy,
Our best guess on this is a Camouflaged Looper,
Synchlora frondaria.

Letter 3 – Camouflaged Looper

Subject: Camouflage Looper?
Location: Tulsa, Oklahoma
August 25, 2016 10:43 pm
Hi — Love your site — thanks for all your work. I found this little guy while I was taking photos at a pond near Tulsa, OK, a few weeks ago.

At first, I couldn’t figure out what it was because it was in the pink tufts of the flower. But then, I used a blade of grass to coax it out onto a leaf. Once it stretched out, I could see it was an inchworm.

I’d never seen one like this before!!
Do you know if the “camouflage” bits get stuck on passively as the inchworm crawls around, or does the worm actively attach them?
Thanks,
Signature: Terrie

Camouflaged Looper
Camouflaged Looper

Dear Terrie,
Thanks for the compliment and thanks for sending in your awesome images of a Camouflaged Looper,
Synchlora aerata, or another member of the genus.  According to BugGuide

“Caterpillar adorns its body with plant fragments, usually flower petals, to camouflage it as it feeds. It is the only widespread species to do so(2), but from Maryland southwards other Synchlora spp. are also present and only raising to adulthood can yield a definite caterpillar ID.” 

We suspect the caterpillar uses silk to attach the flower bits to its body.

Camouflaged Looper
Camouflaged Looper

Letter 4 – Colorful Inchworm may be Meris alticola

Subject: Colorado Caterpillar
Location: 11-mile Canyon outside of Lake George, Colorado
June 23, 2016 8:10 am
Hey Bugman!
I have no idea what kind of caterpillar this is! Or what kind of moth/butterfly it will become? I tried all of my bug books and online resources.
This little guy was found in an 11-mile Canyon in Colorado.


Thank you!
Signature: Frankie

Barberry Geometer
Colorful Inchworm:  Meris alticola perhaps

Dear Frankie,
Because of the reduced number of prolegs, your caterpillar is easily identified as an Inchworm or Spanworm in the family Geometridae, though its colorful markings make it unusual in that family, most of whose members have caterpillars that are green or brown and effectively mimic twigs. 

At first we thought we had correctly identified your Inchworm as a Barberry Looper or Barberry Geometer, Coryphista meadii, based on this BugGuide image, but we remembered identifying a similar Inchworm in the past and we could not find one in our archives. 

We searched our archives for “colorful Inchworm” and we found this posting of Meris paradoxa that looks possible as well, but the species is only reported from Southern Arizona according to BugGuide

The related and similar-looking Meris alticola is also pictured on BugGuide, and it is reported on BugGuide from Colorado, so of the three, our money is on Meris alticola

Letter 5 – Curve-Toothed Geometer with Eggs

Subject:  Moth with eggs
Geographic location of the bug:  Mississippi
Date: 08/02/2018
Time: 04:46 PM EDT
Your letter to the bugman:  This moth laid its eggs on the wall right next to my front door, so it was hard to miss. It looks a bit like the Early Thorn moth, but as far as I can tell from my Google searches, they are not supposed to be in North America, so I must be mistaken.

However, I can’t find a picture of any other moth that is similar so I thought I’d write to you. I have a young child and thought we might have fun keeping track of the eggs as long as the caterpillars that emerge aren’t the kind that sting.

If they are I’ll know to be more cautious.
How you want your letter signed:  Thanks for all you do,

Curve-Toothed Geometer with Eggs

You are most welcome.  We quickly identified this Curve-Toothed Geometer, Eutrapela clemataria, on the Insect Identification site where it states:  “The only moth in its genus, the Curve-Toothed Geometer Moth has many distinctive markings that should help in identifying it.

When at rest with wings flat, a definitive line that crosses from left to right stops short of reaching the edges of the wings. This line separates the dark brown coloring near the head from the lighter brown color at the edge of the wings.

The outer edge of the forewings curves downward and ends in a nubby point, or tooth, at the tips of the wings. The hindwings have scalloped edges.  A young caterpillar has a brown body that becomes darker and more purple as it ages.

It eats the leaves of common trees like ash, oak, and maple. This easily accessible food source makes it almost effortless when expanding its range. Two generations are produced each year in warmer climates.

Adults are active from late spring to late summer in wooded areas across the continent.”  The green eggs are very distinctive, so we attempted to look for images of eggs, and we found the same images of the green eggs on both BugGuide and The Moth Photographers Group

To the best of our knowledge, no Geometer caterpillars, known as Inchworms or Spanworms because of their manner of locomotion, pose a danger to humans.  If you decide to try to raise some caterpillars, we would urge you to transfer the majority of the hatchlings to one of the mentioned host trees and try raising about 20 or so in captivity.

Letter 6 – Cankerworms: Possibly Linden Looper Dropping From Trees in Minnesota

Subject: Caterpillar id
Location: Big Lake, Minnesota
May 30, 2016, 3:29 am
Good morning. My sister has caterpillars in her semi-woodland garden in Big Lake Minnesota that are literally dropping from the trees (pine and ornamentals) on the margin of the woodland. They seem to be most active now – mid-May. It is her first summer there so cannot say whether this is unusual.


Signature: Lorna

Ed. Note:  We had an offline exchange with Lorna since the image attached to the original email was a Black Arches Caterpillar from our site.  We finally received the correct image.

Oops. I don’t know how that happened – I am sorry. Here it is:

Inchworms dropping from trees
Cankerworm dropping from trees

Dear Lorna,
The general term Cankerworm is used to describe several species of Inchworms or Spanworms that feed in trees and drop to the ground.  According to Virginia Green Lawn Care

“The term ‘canker worm’ is used, not to describe a single caterpillar, but a group of inchworms that cause damage to many different ornamental and fruit trees. … These leaf eating insects are not only a nuisance; they can cause great damage or even destroy a grown tree over a period of time.

You may have run into one dangling from a silk thread as you walked under a tree. It is a battle between canker worms and the trees you love and have planted and nurtured.  When heavy populations are present, they can completely defoliate a tree in just a few weeks. This is when you need to step in.” 

The individual in the new image you attached looks like the Linden Looper, Erannis tiliaria, a species that according to BugGuide feeds on:  “Deciduous trees, including apple, ash, beech, birch, elm, maple, oak, poplar, Prunus and Ribes.”

Authors

  • Daniel Marlos

    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.

  • 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.

16 thoughts on “Are Inchworms Caterpillars? Unraveling the Mystery”

  1. How sad. I see the trolls can’t resist even these hallowed pages. I’m not even sure if this merits a Nasty Reader award, to be honest. The crying at the computer is just way too over the top!Good thing school will be back in session shortly!
    Bugophile

    Reply
  2. Surely there was only one proper response for you guys to have made isn’t there?

    You didn’t take that, someone else made that happen.

    Expect the entitlement generation to get even more obnoxious if you guys allow the welfare state to keep propping them up for another four years. We are desperately trying to rid ourselves of the same type of government down under but unfortunately we don’t get an election till next year, barring some stroke of good fortune.

    Reply
    • You have it all wrong. This has absolutely nothing to do with any non-existent “nanny-state” that could have caused such crassness. This has absolutely everything to do with horrid parenting. Whether it was non-existent parenting or helicopter parenting could be debatable, but one doesn’t learn such behavior from a government. One learns that kind of behavior as a child, from the actions or inactions of parents.

      Reply
  3. So sorry you have to be berated by the impatient one with a plagerized photo, while others wait patiently with their legitimate requests! (I have had similar emails from someone with even worse grammar expecting instant responses, so I understand what it’s like!)
    I am not surprised you have not responded to my request a couple of weeks ago (during the height of your busy season) to identify my drawing of an unusual white beetle with seven green spots. After all, how do you know I didn’t just make it up to try to stump you? But your identification of a flower fly from a drawing has given me renewed hope. Therefore, I thought I should write again and let you know that I mailed my daughter a copy of the drawing which I made by following her instructions over the phone, to see if I even came close. Amazingly, she reports that my drawing is almost identical to the one she made while actually looking at the insect, except that the spots on hers are slightly more oval. One of these days if I get a chance, I hope to get out to see her. If she has not deleted her blurry attempt to photograph the critter, I will see if I can download it onto something and get it to a computer so I can send it to you to back up the drawing. In the mean time, I understand you are very busy at this time of year, so I will continue to be patient! Keep up the good work.

    Reply
    • Thank you for your support. We were called out of the office for several days for a family wedding out of town, and we haven’t even checked the emails we received while away. We are starting with the comments. If we cannot locate your drawing, please resend it and label it as “drawing of beetle” to get our attention.

      Reply
  4. Daniel,

    So sorry to hear that you are subjected to this childish person’s rants.

    I found this at http://www.urbandictionary.com:

    1. This hideously misspelled derivation of ‘f*****’ [an even more derogatory word unless you are in Great Britain and referring to a British meatball commonly made of pork offal] is primarily used by uneducated rednecks who fail to see the irony of calling someone a derogatory name but having no idea how to say the word.

    Keep up the good work! Anna

    Reply
  5. I don’t dislike bugs but I don’t really like them either. Know what I mean?
    Anyway, I love the info here and the fact that people take extra time in their busy schedules for something they love really gives the visitor a true sense of understanding for your passion. Clearly, that was not how Alexis felt about your unresponsiveness. Everyone knows that yelling and name calling always gets you exactly what you need… A swift kick in the pants!

    Sorry, couldn’t help myself. Keep up the good work!

    Reply
  6. I had a good laugh at this, thanks. Do you think he was crying and staring at the computer for the whole time between 3:19 and 5:10?

    Reply
  7. Wow…so rude .
    I feel sorry for those who put themselves in an awkward situation.
    some people needs help.

    Appreciating what you’re doing bug man, keep up the good work.

    Reply
  8. *standing ovation*
    I have not encountered such a well-constructed put-down to outright over-the-top rudeness in a long time! Well *bleeping* done! I haven’t laughed so hard in a long while, and I needed it. *two thumbs up* Thank you!

    Reply

Leave a Comment