Where Do Inchworms Come From? Unraveling Nature's Tiny Secret

Inchworms, also known as cankerworms or loopers, are the larval stage of several species of geometrid moths. Interestingly, these small creatures play a significant role in nature as they assist in the decomposition of plant material. You might have seen these fascinating critters inching along leaves and branches, but have you ever wondered where they come from?

To better understand the origins of inchworms, it’s essential to delve into their life cycle. Adult geometrid moths lay their eggs on the branches and leaves of trees and plants. When these eggs hatch, the larvae, which are the inchworms you often encounter, emerge.

These inchworms have a peculiar method of locomotion, which involves looping their bodies into a shape resembling the letter “U.” As they progress through their life cycle, the inchworms will eventually transform into adult moths, completing their journey and allowing the cycle to continue.

Understanding Inchworms

Characteristics of Inchworms

Inchworms, also known as loopers or measuring worms, are caterpillars from the family Geometridae, which falls under the order Lepidoptera. An inchworm’s body is color, smooth, cylindrical, and hairless, allowing it to effectively camouflage itself in various environments. The distinguishing feature of inchworms, as opposed to other caterpillars, is their unique “looping” motion when they move around.

Some key features of inchworms include:

Unique looping movement
Caterpillar stage in the geometridae family
Effective camouflage thanks to their smooth, cylindrical and hairless body

Different Species of Inchworms

There are more than 1,400 species of inchworms across North America, and they feed on a wide range of deciduous trees, shrubs, and ornamentals. Some notable species of inchworms are:

Cankerworms: Cankerworms can cause significant defoliation of various deciduous landscape and forest trees during large outbreaks.
Spring and Fall Cankerworms: These inchworm species differ in their number of prolegs (false legs) on their abdomens and the time they’re active, with one peaking in the spring while the other is active in the fall.
Spanworms: Spanworms may specifically target conifers, while others focus on deciduous trees and shrubs.

Species	Prefered Host	Appearance
Cankerworms	Deciduous trees	Varies, but generally cylindrical and hairless
Spring Cankerworm	Deciduous trees	Maybe yellow-green to brownish to blackish with a white stripe on the side
Fall Cankerworm	Deciduous trees	Can range from light green to dark green to black
Spanworms	Conifers or Deciduous	These may vary depending on the specific species within the spanworm group

You may come across various species of inchworms depending on your location and the type of vegetation in your area. By understanding their characteristics and preferred host plants, you’ll be better equipped to identify and manage these fascinating caterpillars.

Life Cycle of Inchworms

From Egg to Larvae

Inchworms, also known as cankerworms, start their life cycle as eggs. Adult moths lay their eggs on the branches and leaves of trees. When the eggs hatch, tiny larvae emerge. These larvae have a unique appearance with fewer prolegs than other caterpillars, which results in their distinctive “looping” movement.

Some characteristics of inchworm larvae:

Yellow-green, brownish, or blackish color
A white stripe may run along the side of the body
Feed on a variety of trees and shrubs

Pupal Stage

After a period of feeding and growing, the inchworm larvae enter the pupal stage. They transform into pupae, encased in protective cocoons. This stage is crucial for their growth and development into adult moths. During this time, they undergo a process called metamorphosis that changes their bodies into a completely new form.

Key features of the pupal stage:

Encased in protective cocoons
Undergo metamorphosis

The Adult Moth

Once the pupal stage is complete, the transformed inchworm emerges as an adult geometer moth. Adult moths have fully developed wings, allowing them to fly and reproduce. They typically have a short life span and do not feed during this stage. Their primary goal is to mate and lay eggs, continuing the life cycle.

Features of adult geometer moths:

Fully developed wings
Short life span
Do not feed in this stage

Remember, it is important to familiarize yourself with the life cycle of inchworms as understanding their phases can assist you in dealing with them in your garden or landscape effectively.

Habitat and Diet of Inchworms

Inchworms, also known as measuring worms or spanworms, are a part of the geometer moth family. They can be found in various habitats, feasting on different types of plants.

You can observe inchworms on several trees like oak, maple, and mulberry. They fancy fruit trees as well, and bushes in your garden aren’t safe either. Inchworms enjoy nibbling on garden plants, leaves, and twigs, making them a nuisance for many gardeners. They may also be drawn to your vegetable garden.

These little creatures have diverse food preferences, depending on their species. For example, some inchworms specifically target conifers, while others prefer feasting on deciduous trees. Certain species may even feed on flowers or invade your blueberry bushes.

Here’s a comparison table to help you understand inchworms’ habitat preferences:

Habitat	Food Source	Example
Trees	Leaves & twigs	Oak, maple
Fruit Trees	Leaves & fruits	Mulberry
Bushes	Leaves	Garden bushes
Garden Plants	Leaves & flowers	Vegetable garden
Conifers	Leaves & needles	Pine tree
Deciduous Trees	Leaves	Birch tree

Remember to keep a close eye on your plants and trees to spot any signs of inchworms. Staying informed about their habitat and diet will help you address an infestation if it occurs in your garden.

Understanding the Unique Movement of Inchworms

Looping Motion

Inchworms, also known as loopers, move in a distinctive looping motion. This movement is due to their unique body structure, which includes both legs and prolegs. Let’s take a closer look at how these tiny creatures achieve their fascinating motion.

To begin, inchworms have two main types of legs: the true legs at the front and the prolegs at the rear. As they move, the inchworm first extends its body fully, using its true legs to anchor onto the surface. Next, it contracts its body, bringing the prolegs closer to the true legs. This establishes the “loop” shape that gives them their name.

Here are some key features of inchworm movement:

Distinct looping motion
True legs and prolegs work together
Body contracts and extends in a coordinated manner

A comparison of the different leg types involved in inchworm movement:

Type of Legs	Location on Body	Role in Movement
True Legs	Front	Anchor onto surface
Prolegs	Rear	Help create loop shape

So, the next time you observe one of these fascinating little creatures, you can appreciate the unique interaction between the inchworm’s legs and prolegs that creates its signature looping motion.

Inchworms as Pests

Inchworms in Garden Plants

Inchworms, also known as cankerworms, can cause damage to various plants in your garden. These pests feed on ornamentals like rhododendron, native trees, and shrubs. Their feeding habits may result in:

Defoliation of trees and shrubs
Stress to the plants
Decreased crop yields

The infestation can especially impact your vegetable garden, leaving you with less produce to harvest.

Methods of Control

Controlling inchworms is crucial to maintain a healthy garden. Here are some methods to consider:

Bacillus thuringiensis (Bt): This non-toxic bacteria specifically targets inchworms, leaving other beneficial insects unharmed. Bt can be easily applied to your plants as a spray.
Trichogramma wasps: Introducing these beneficial insects in your garden helps control inchworm populations. The wasps are parasitic and lay their eggs inside inchworm eggs, helping reduce future generations.
Chemical pesticides: In cases of severe infestation, using chemical pesticides may be necessary. However, they should be used cautiously, as they can harm beneficial insects and the environment.

Keep in mind that combining these methods can lead to better results in controlling inchworms and maintaining a healthy garden.

Here’s a comparison table for your reference:

Control Method	Pros	Cons
Bacillus thuringiensis	Non-toxic, targets inchworms	May need repeated applications
Trichogramma wasps	Targets inchworms, reduces population	May take time to establish in the garden
Chemical pesticides	Effective in severe infestations	Can harm beneficial insects and the environment

To manage inchworm infestations, use these methods wisely. With proper control strategies, you can safeguard your garden plants and ensure they remain healthy and stress-free.

Natural Predators of Inchworms

Birds and Spiders

In nature, inchworms face various predators, such as birds and spiders. Birds, including songbirds and woodpeckers, feed on inchworms as a nutritious meal. On the other side, spiders sit and wait to ambush these wriggly creatures in their webs.

You might notice that inchworm populations fluctuate depending on the presence of these predators in your garden. They play a critical role in controlling inchworm population.

Other Insect Predators

Inchworms also fall prey to several carnivorous insects. Some of the significant ones are:

Yellow jackets: These wasps are prominent predators of inchworms, attacking and feeding on them.
Paper wasps: Similar to yellow jackets, they hunt for inchworms as part of their diet.
Sawfly larvae: These insects consume inchworms and sometimes compete with them for food resources.
Earwigs: They prey on various insects, including inchworms, which they consume to supplement their diet.

Here’s a comparative table of the predators:

Predator	Hunting method	Impact on inchworm population
Birds	Active hunters, catch inchworms by sight and movement	Significant
Spiders	Passive hunters, ambush inchworms in webs	Moderate
Yellow Jackets	Active hunters, attack and feed on inchworms	Moderate
Paper Wasps	Active hunters, feed on inchworms	Moderate
Sawfly larvae	Competition for food resources, consume inchworms	Low
Earwigs	Generalist predators, consume inchworms as supplement	Low

Remember that a balanced ecosystem with these natural predators is essential in controlling inchworm populations and maintaining a healthy environment for your garden.

Additional Information on Inchworms

Inchworms are fascinating creatures that can be observed during different seasons, such as spring and fall. These caterpillars are known for their unique “looping” motion as they move. Here is some additional information to help understand them better.

Activities and Behavior

While some inchworm species are active during the day, others are nocturnal and prefer to go about their business at night. This can vary depending on the specific species. They have a fascinating defense mechanism: when threatened, they stand straight, blending in with the environment to resemble a twig.

Physical Features

Inchworms have a distinctive body structure. They possess only two or three pairs of true legs at the front and a few pairs of prolegs at the back, causing their looping movement. The colors of spring and fall cankerworms, a type of inchworm, can vary from yellow-green, brownish, and blackish, with many sporting a white stripe running the length of their bodies.

Lifecycle and Environment

During their life cycle, inchworms produce silk, which they use to pupate. Once they metamorphose into moths, their wingspans vary based on the species. They lay their eggs on trees and plants, which offer sustenance to the growing caterpillars.

Examples of inchworm habitats:

Ornamental plants, such as rhododendron
Coniferous trees
Deciduous trees and shrubs

In conclusion, inchworms play a critical role in the ecosystem. It’s essential to learn more about these fascinating critters to promote their conservation and understanding.

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 – Inchworm

Subject: Tiniest inchworm
Location: South Central Kentucky
April 21, 2015 10:50 am
This morning I found this inchworm near my neck. We have a garden and chickens and many new fruit trees. Also there was a stray puppy here yesterday. So between all that, no clue where this came from. Found it on April 21. It has been about 65-80 degrees this last week with a LOT of rain. This worm is about the size of a thread and about 1/4 to 1/2 inch long. It is black with no markings visible to the eyes. The pic isn’t very good cuz the camera couldn’t focus close enough. Thank you for your reply but I understand if you don’t… Have a good day!
Signature: Reneé

Dear Reneé,
Though we are unable to provide you with a species identification, we are able to provide you with a response. As you have indicated, this is an Inchworm or Spanworm in the family Geometridae. The larvae from this family is characterized by having only two pairs of prolegs, three pairs fewer than most caterpillars, hence their locomotion is affected. They move by a looping action as your image indicates. Here is the explanation on BugGuide: “[Geometridae Larvae] generally have only two pairs of prolegs (at the hind end) rather than the usual five pairs in most lepidoptera; the lack of prolegs in the middle of the body necessitates the peculiar method of locomtion, drawing the hind end up to the thoracic legs to form a loop, and then extending the body forward.” This Inchworm probably fell from a tree in your garden.

Letter 2 – Inchworm in England

Subject: strange long brown bug!
Location: Wiltshire, England
November 13, 2013 5:05 pm
I’ve just found this clinging onto a photo in my room, looks like a twig but has four stubby legs at the front… Never seen anything like it! Hope you can help! Got to admit I don’t really want him in my room but don’t have the heart to put him outside in winter…
Thankyou! Emily 🙂
Signature: Emily

Hi Emily,
This is the caterpillar of a moth in the family Geometridae. They often mimic twigs and they are called Inchworms or Spanworms because of the manner in which they move, bunching up the body and then stretching out again.

Letter 3 – Inchworm from Australia

Subject: What is this caterpillar?
Geographic location of the bug: Sydney, Australia
Date: 03/20/2021
Time: 02:49 AM EDT
Your letter to the bugman: Hi
Found this little agile one eating my curry leaves. Want to know if it is a pest amd curious about it’s species. Thank you.
How you want your letter signed: Curious gardener

Dear Curious Gardener,
This is an Inchworm or Spanworm in the family Geometridae. We believe it might be Hyposidra talaca based on an image posted to the Butterfly House website. Though curry is not listed as a food plant, the site indicates: “It is polyphagous, eating the foliage of many plants including the crops.”

Thank you so much for the information.

Cheers,

Rashmi

Letter 4 – Inchworm

Subject: It moved!
Location: Slatington, PA
May 28, 2012 8:53 am
My mother found this thing outside of her house. She thought it was stick, and rightly so. And then it moved! EW! Please tell me what it is, I have never seen anything like this!
Signature: Mandy

Hi Mandy,
This is an Inchworm or Spanworm, the caterpillar of a moth in the family Geometridae. They get their common name from the manner of locomotion. As you can see in the photo where the Inchworm is up-side-down, there are three pairs of true legs near the head and only two pairs of false legs or prolegs near the posterior end of the body. Most caterpillars have five pairs of prolegs and that enables them to move in an oscillating manner. There is a drawing on the Enchanted Learning website that illustrates the anatomy of a typical caterpillar. Inchworms need to crawl forward on their true legs and then loop the rear end of the body forward. Many Inchworms are excellent twig mimics, and they are known to grasp a stem with the prolegs and stick the rest of the body straight out exactly like a twig. Our Bug of the Month Posting for April 2011 was the Inchworm and the posting illustrates both the manner of locomotion and the twig mimic behavior.

Letter 5 – Inchworm

Subject: Caterpillar
Location: Pittsburgh PA
October 14, 2013 2:27 am
Tiny, black and brown. Little more than half inch? I don’t think he has any hair
Signature: Natalie c

Hi Natalie,
This is an Inchworm or Spanworm, a caterpillar in the family Geometridae. Caterpillar in this family generally possess but two pairs of prolegs on the rear portion of the abdomen. Most caterpillars have five pairs of prolegs spread out along the abdomen. The method of locomotion of Inchworms differs from the typical caterpillar because of the fewer number of prolegs. BugGuide describes it thus: “larvae generally have only two pairs of prolegs (at the hind end) rather than the usual five pairs in most lepidoptera; the lack of prolegs in the middle of the body necessitates the peculiar method of locomtion, drawing the hind end up to the thoracic legs to form a loop, and then extending the body forward.” Inchworms are also called Measuringworms.

Letter 6 – Inchworm from Japan: Milionia basalis

Subject: Measuring Worm Moths Inchworm
Location: Okinawa Japan
December 6, 2012 2:08 am
Here is another copy of the image I sent in for request before I realized that this is the inch worm for the moth images I sent. I am not sure if you want to put it with the moth images or if you want to put it in the caterpillar area. I took this shot in May of 2010 in Okinawa.
Thanks!
Signature: Richelle

measuring_worm_japan_richelle — Inchworm: Milionia basalis

Dear Richelle,
Thanks so much for resending this image. We never recall seeing it, but on busy days, we can only read a fraction of the mail that arrives. This is a marvelous addition to the adult Milionia basalis you have already submitted.

Letter 7 – Inchworm from Japan

Subject: A mystery caterpillar on our raspberries…
Location: Osaka, Japan
May 28, 2014 10:16 pm
We’re in Osaka, Japan, living in a 10th floor apartment, so whatever laid that egg was a good flier. It’s about 7 cm long, and chowing down on raspberry bushes. Any idea what it will become? The picture was taken about a week ago (May 24th).
Thanks!
Signature: Chris Gladis

Hi Chris,
This appears to be an Inchworm or Spanworm in the Moth family Geometridae. Most caterpillars in this family have only two pairs of prolegs which causes them to move in a most characteristic manner, where the caterpillar stretches out with is true legs and then moves the entire hind section in one step, inching along and causing the body to loop. We are not certain of the species. Most Geometrid Moths are dull in color, but some are quite colorful.

Letter 8 – Inchworm: Meris paradoxa

Subject: White caterpillar with black stripes, black dots and yellow dots
Location: Northern Arizona
May 25, 2014 10:00 am
I found several of these caterpillars in a pinstemon plant in Flagstaff Arizona.
Signature: Adriana

Dear Adriana,
This is an Inchworm or Spanworm in the family Geometridae, and the common name for the caterpillar is because of the number of prolegs, two pairs, resulting in a manner of locomotion where the caterpillar stretches out with is true legs and then moves the entire hind section in one step, inching along and causing the body to loop in the manner illustrated in one of your images. Interestingly, our first attempt at a species identification, thank to your inclusion of the food plant Penstemon in your description, produced a matching image from our archive that has been unidentified to the species level since April 2008. We hope to remedy that identification plus your identification today. Without too much trouble, we located Meris paradoxa on BugGuide. The host plant is listed as snapdragon, and Penstemon is in the snapdragon family Plantaginaceae.

Thank you so much for solving the mystery. I looked all over the internet for a couple of days before I asked for your assistance. Wow, such a colorful caterpillar turns into such a drab moth.

Letter 9 – Inchworm, possibly Oak Besma

Big Ugly Worm
Hi. We have been enjoying your site very much since we discovered it a few days ago. Now we have found a weird ugly bug we would like to have identified. We live in northeastern PA. Our area is heavily woodedbut we are not near water. This THING was seen “inching” along on the concrete pad by my pigeon lofts. It moves by bending itself up into a bow shape, then reaching out with the front. It’s like an inchworm, only much bigger and uglier. It has 4 caterpiller-like feet (my son says they are pseudopods) on the back end, and about 8 claw-like feet on the front. It SCARED us! What is it?
Thank you,
Sue and David

Hi Sue and David,
You can stop being scared of your Spanworm or Inchworm, one of the Geometrid Caterpillars. They are very difficult to positively identify. Our best guess is the Oak Besma, Besma quercivoraria, which eats a wide variety of forest trees besides oaks including conifers. There are conspicuous wartlike swellings that help it to mimic a twig that has had the leaves drop off, especially when the caterpillar rests by streching straight out at an oblique angle. Here is a page full of Geometrid Caterpillars from the Caterpillars of Eastern Forests website.

Letter 10 – Inchworms from India

Subject: Inchworm Mayhem
Location: Mumbai, India
April 29, 2015 7:34 am
Dear Bugman,
These inchworms have wreaked havoc in my tiny balcony garden, fairly shredding my spider-plants to bits. Could you help id? I understand from your site that inchworms are geometrid moths caterpillars. It’s full summer now in India, and the photos are today’s (April 29). Another couple of days and it would’ve been ‘May’hem quite literally and figuratively 😀
Regards,
Signature: Ankush

Dear Ankush,
Is your Spider Plant a Chlorophytum species like that posted on Wikipedia? Knowing the food plant is often a big help with identifying caterpillars and other plant feeding insects. We attempted a search with the genus name of the Spider Plant and the family name Geometridae, but to no avail. You image is stunning and clearly shows the looping action the Inchworm uses to move about, a result of having fewer sets of prolegs than the typical caterpillar.

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.