Are Caterpillars Insects? Unraveling the Mystery

Caterpillars are fascinating creatures often found in our backyards and gardens.

These are actually insects, and they are the larval stage of butterflies and moths, belonging to the order Lepidoptera.

As they cannot fly or run away, it’s easy to observe their intriguing size, color, and body shape up close.

Notable features of caterpillars include:

• A wide range of colors, patterns, and body shapes
• Ability to transform into butterflies or moths during metamorphosis
• Prolegs, short fleshy leg-like appendages used for movement
• Silk glands, which produce silk for cocoon formation in some species

Now, you might be wondering whether or not these intriguing creatures are insects. That’s exactly what we are going to discuss in this article.

Are Caterpillars Insects?

Caterpillars are indeed insects, belonging to the class Insecta within the phylum Arthropoda. Arthropods are invertebrates characterized by having an exoskeleton, segmented bodies, and jointed appendages.

Caterpillars share common characteristics with other insects, such as having three main body parts – the head, thorax, and abdomen – and six jointed legs.

However, caterpillars also possess unique features, such as their numerous, often colorful, fleshy protrusions called “scoli” or “tubercles” found in some species.

Here is a comparison table between caterpillars and other arthropods:

Feature	Caterpillars	Other Arthropods
Phylum	Arthropoda	Arthropoda
Class	Insecta	Varies (e.g., Crustacea, Arachnida, Myriapoda)
Segmented body parts	Head, Thorax, Abdomen	Varies (e.g., Head, Thorax, Abdomen, Cephalothorax
Legs	6 true legs, prolegs	Varies (e.g., 8 legs in spiders, 10+ in centipedes)

Characteristics of caterpillars:

• Belong to the order Lepidoptera
• Larval stage of butterflies and moths
• Typically herbivorous
• Have an exoskeleton with tiny hooks on their feet for climbing

A caterpillar’s legs include six true legs and an additional number of stumpy prolegs, which help with movement and grasping surfaces.

The six true legs are located on the thorax, while the prolegs are situated on the abdomen.

Caterpillars, as insects and arthropods, display a fascinating diversity in size, color, and body shape, making them an intriguing subject of observation and study in gardens and nature.

Caterpillar Life Cycle

Egg

Caterpillars begin their life as eggs laid by female butterflies or moths. The eggs are often attached to plants that will provide food for the hatched larvae. They come in various shapes, sizes, and colors, depending on the species.

Larva

Once the eggs hatch, the caterpillars emerge as larvae. This stage is often called the “feeding stage” as the primary goal for the larvae is to eat and grow.

Caterpillars undergo a process called instar, going through multiple molts, shedding their exoskeletons as they grow larger. Some common characteristics include:

• Range in size from ½ to 4 inches (13-102mm) in length
• Vary in color from pink, brown, green, blue to black
• May have spots, stripes, or unique markings to identify species

Pupa

After the larval stage, caterpillars enter the pupa stage. During this stage, they undergo metamorphosis, transforming into either a butterfly or a moth depending on their species. Pupae can be found in different forms such as:

• Chrysalis: Enclosed structure mostly for butterfly species
• Cocoons: Silk-wrapped enclosures created by some moth species

Adult

Upon completion of the pupa stage, a fully-developed butterfly or moth emerges. As adults, their primary purpose is to reproduce and lay eggs, thus beginning the life cycle anew.

Table showing food and behavior of different stages of a caterpillar

Stage	Food	Behavior	Duration
Egg	N/A	Attach to host plant	Varies
Larva	Host plant leaves	Eat and grow	Weeks
Pupa	N/A	Metamorphose	Days-Weeks
Adult	Nectar (butterflies/moths)	Reproduce, lay eggs	Weeks

Anatomy and Appearance

Prolegs and True Legs

Caterpillars, as insects, have three pairs of true legs. These legs are jointed and located at the front of their body.

In addition, they possess prolegs, which are fleshy, unjointed appendages. Prolegs can be found towards the rear of their body and are used for gripping surfaces.

Key features of prolegs include:

• Stubby appearance
• Equipped with tiny hooks for better grip

Head and Eyes

Caterpillars have a well-defined head, housing vital organs such as the brain and mouthparts.

Their mouth is equipped with powerful mandibles for chewing leaves. Their eyes, known as stemmata, are simple eyes and function differently from those of adult insects.

Caterpillars typically have six stemmata on each side of their head.

Antennae and Markings

Caterpillars also have antennae, though small and not used for sophisticated sensing abilities. They primarily use these antennae for basic tactile sensing.

Their markings and color can vary greatly, helping them with camouflage, warding off predators, or mimicking other dangerous creatures.

Below is a comparison table of caterpillar anatomy features:

Feature	Function	Example
Prolegs	Gripping surfaces	Movement on leaves
True Legs	Mobility and manipulation	Grasping twigs
Head	Housing vital organs like the brain and mouthparts	N/A
Eyes	Basic vision using stemmata	Sensing light
Antennae	Tactile sensing	Touching surfaces
Markings	Camouflage, predator deterrence, or aposematic coloration	Mimicking snakes

Caterpillar Diet and Feeding Habits

Caterpillars are herbivores, primarily feeding on plant materials. Their diet consists of host plants, including leaves with high nutritional value.

Here are some features of their feeding habits:

• Host plants: Caterpillars are selective eaters, often choosing specific plants to consume.
• Leaves: They are known to consume entire leaves, leaving behind only the major veins.

There is a variety of caterpillar species, each with distinct dietary preferences. Moth caterpillars, for example, have diverse eating habits, ranging from generalist feeders to specialists.

Some well-known caterpillar species and their host plants are:

• Monarch caterpillars: Milkweed
• Woolly bear caterpillars: A variety of plants, including grasses and clovers
• Eastern tent caterpillars: Cherry and apple trees

A comparison between generalist and specialist caterpillars:

	Generalist Caterpillars	Specialist Caterpillars
Diet	Wide range of host plants	Limited to specific host plants
Adaptability	Adapt easily to plant changes	Less adaptable due to specific diet
Nutrition	Less dependent on plant nutritional value	Rely on high nutrition from specific plants

Caterpillar Defense Mechanisms

Caterpillars can easily blend in with their surroundings, thanks to their color and appearance. This makes it difficult for predators to spot them. For example, the saddleback caterpillar has a green and brown coloration that resembles a saddle, providing effective camouflage.

Pros:

• Helps avoid predation
• Increases survival rate

Cons:

• Limited to specific environments
• May not work against all predators

Horns and Hair

Many caterpillars have additional physical features such as horns and hair for defense.

Some caterpillars incorporate their body hairs into the silk of their cocoon to deter predators. These hairs can also be irritating to the skin of potential predators.

Pros:

• Physical deterrent for predators
• Provides added protection

Cons:

• Not all caterpillars have these features
• Could be harmful to humans on contact

Toxins and Venom

Some caterpillars, like the puss caterpillar, can deliver potent stings due to toxins in their hairs or spines. These stings may cause skin rashes and extreme pain, deterring predators from attempting to eat them.

Pros:

• Effective against predators
• Reduces likelihood of being eaten

Cons:

• Can be harmful to humans
• Potentially dangerous to handle

Table Showing Different Defense Mechanisms of Caterpillars

Defense Mechanism	Pros	Cons
Coloration	Helps avoid predation	Limited to specific environments
	Increases survival rate	May not work against all predators
Horns and Hair	Physical deterrent for predators	Not all caterpillars have these features
	Provides added protection	Could be harmful to humans on contact
Toxins and Venom	Effective against predators	Can be harmful to humans
	Reduces likelihood of being eaten	Potentially dangerous to handle

Caterpillar and Moths

Moth Caterpillars and Species

Moth caterpillars are the larval stage of moths. They come in various sizes, colors, and patterns.

Some characteristics of moth caterpillars are:

• Range in size from ½ to 4 inches (13-102mm) in length
• Available in colors like pink, brown, green, blue, and black
• Display spots or stripes

A well-known example of a moth caterpillar is the Puss Caterpillar, also known as Megalopyge opercularis.

Moth Life Cycle

Moths undergo complete metamorphosis in 4 stages:

1. Egg: Female moths lay eggs, which later hatch into caterpillars.
2. Larva (caterpillar): During this stage, the caterpillar feeds and grows rapidly.
3. Pupa: The caterpillar forms a chrysalis or cocoon and transforms into an adult moth.
4. Adult: The adult moth emerges from the cocoon, ready to mate and lay eggs.

Stage	Key Features
Egg	Female moths lay eggs
Larva	Caterpillars feed and grow
Pupa	Enclosed in a chrysalis, caterpillar transforms
Adult	Adult moth emerges, ready to mate and lay eggs

During the caterpillar stage, the moth larva feeds on plants and can sometimes cause damage to ornamentals and trees, as seen in caterpillars on ornamental plants.

Caterpillar and Butterflies

Butterfly Caterpillars and Species

Butterfly caterpillars are the larval stage of butterflies. They are distinct from moth caterpillars. Different species of butterfly caterpillars can be easily identified by their unique appearances.

Some facts about butterfly caterpillars:

• Appearance: They can change coloration and appearance after each molt
• Feeding: Caterpillars feed on specific host plants depending on the species

Monarch Butterfly and Caterpillar

The Monarch butterfly is a well-known species with a unique relationship with the milkweed plant. Both the Monarch caterpillar and adult butterfly have fascinating characteristics:

Monarch Caterpillar:

• Feeds on milkweed leaves
• The ingested milkweed sap makes them distasteful to predators

Monarch Butterfly:

• Adult stage of the Monarch caterpillar
• Pollinates milkweed plants
• Known for its incredible long-distance migration

Comparison of Monarch Caterpillar and Butterfly:

Feature	Monarch Caterpillar	Monarch Butterfly
Food	Milkweed leaves	Nectar from milkweed flowers
Role	Growth and development	Pollination and reproduction
Predator defense	Distasteful due to milkweed ingestion	Inherits distaste from caterpillar stage

The Monarch butterfly and caterpillar showcase a remarkable example of adaptation and coevolution with the milkweed plant.

Overall, caterpillars, as the larval stage of butterflies, play a crucial role in the life cycle of these beautiful insects.

Monarch Butterfly

Caterpillars as Pests

Agricultural Pests

Caterpillars, the larvae of butterflies and moths, can cause significant damage to various crops. Some common crop-feeding caterpillars include:

• Bollworm: Affects cotton, tomato, and pepper plants
• Cutworm: Damages corn, tomato, and pepper plants
• Pine processionary: Destructive to pine trees and apple orchards

These pests typically feed on leaves, flowers, shoots, fruits, or even bore into wood, leading to reduced crop yields and quality.

Control and Management

Managing caterpillar pests in agriculture is essential for maintaining healthy and productive crops. Some methods to control these pests include:

• Biological control: Encourage natural predators and parasitoids, such as birds, insects, and spiders, to reduce caterpillar populations.
• Cultural practices: Rotate crops, eliminate weeds, and maintain proper irrigation to create a less favorable environment for caterpillars.
• Hand-picking: For smaller infestations, hand-picking caterpillars can be effective in controlling their populations.
• Insecticides: Use chemical insecticides when other methods are insufficient, or caterpillars have reached larger sizes and are more difficult to control.

Table showing different control measures

Pros	Cons
Biological control is eco-friendly	Takes time to establish
Cultural practices can improve overall plant health	May not be sufficient for large infestations
Hand-picking is cost-effective	Labor-intensive and time-consuming
Insecticides provide fast results	May harm beneficial insects and can lead to pesticide resistance

It is crucial to combine these methods for a comprehensive and sustainable approach to caterpillar pest management.

This way, farmers can protect their crops from significant damage while minimizing the need for chemical interventions.

Caterpillars in the Ecosystem

Caterpillar Predators

Caterpillars face numerous predators in the ecosystem. Some of the most common ones include:

• Birds: Many bird species feed on caterpillars as a primary food source.
• Wasps: Certain wasp species lay their eggs on or inside caterpillars, eventually killing them.
• Spiders: Various spider species prey on caterpillars both by trapping them in their webs and through active hunting.
• Centipedes: These arthropods are known for their predatory behavior and may occasionally prey on caterpillars.
• Snails: Some omnivorous snail species feed on caterpillars.

Contribution to the Environment

Caterpillars play significant roles in the ecosystem, some of which are:

• Decomposition: Caterpillars consume plant material, facilitating the breakdown and recycling of nutrients in the environment.
• Food source: As mentioned earlier, many animals rely on caterpillars for nourishment, forming a crucial component of the food chain.
• Plant population control: By feeding on plants, caterpillars help regulate plant populations in their habitats.

Comparison table showing various caterpillar predators

Predator	Hunting Method	Effect on Caterpillar Population
Birds	Active hunting	Major predator
Wasps	Parasitic egg laying	Moderate threat
Spiders	Web trapping, active hunting	Moderate threat
Centipedes	Active hunting	Minor predator
Snails	Opportunistic feeding	Minor predator

Caterpillars in Culture

Literature and Visual Arts

Caterpillars have been featured in various forms of literature and visual arts.

For example, they are often portrayed as an essential part of a butterfly’s life cycle in children’s books, teaching about growth and transformation.

One famous caterpillar character is from Lewis Carroll’s Alice’s Adventures in Wonderland, where a wise and enigmatic caterpillar helps Alice.

Some nocturnal caterpillars, like the atlas moth and diamondback moth, caught the fascination of artists for their distinct proboscis and unique patterns.

Silkmoth Caterpillar

Silk Production

Silk production is largely dependent on caterpillars, with the domesticated silkworm being the most significant contributor. Let’s take a look at these creatures.

Silkworm:

• Scientific name: Bombyx mori
• Produces high-quality silk
• Mostly feeds on mulberry leaves

Atlas moth:

• Scientific name: Attacus atlas
• Silk used in traditional purposes
• Feeds on several different host plants

Here’s a comparison table for the two moth species used in silk production:

Feature	Silkworm	Atlas Moth
Silk Quality	High, soft, fine	Lower, coarse, wild
Host Plants	Mulberry leaves	Various plants
Cocoon	Used for silk	Silk cocoon not used commercially

Silkworms predominantly contribute to the global silk production, spinning a silk cocoon during its pupate stage.

This silk is later unraveled and woven into fine, luxurious fabric. While atlas moths also produce silk, their cocoons are not suited for commercial silk production due to their coarser and wilder texture.

Conclusion

The world of caterpillars is one of wonder and complexity, revealing a captivating journey of growth and adaptation. They are fascinating insects with diverse characteristics and evolutionary history.

By studying their features, habitats, and ancient fossils, we can better understand and appreciate these intriguing creatures.

Reader Emails

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

Letter 1 – Caterpillar on Lupine: Twirler Moth Caterpillar???

ID caterpillar
I’ve looked at all your caterpillar photos and don’t find this guy. What is it? It is on a bluebonnet (Lupinus texensis.)
Beth Ramey, Wimberley, TX

Hi Beth,
This is just a guess. We did a web search of caterpillar and lupine and found numerous postings regarding the returning lupine population being ravaged by caterpillars after the eruption of Mt Saint Helens.

Though we could not locate a photo of this caterpillar, the description reads: “Much of the lupine damage was attributable to caterpillars of Filatima sp. moths, herbivores that feed on the lupine.

The caterpillar ties lupine leaves together in silken masses to feed on the green tissue, dramatically reducing the number of seeds produced by lupines and, consequently, the rate at which the lupine population can expand.”

This is consistant with your image that seems to show the silken mass on the leaves. We then tried BugGuide, but could not locate the genus, only the family Gelechioidea, and the Family Gelechiidae, Twirler Moths. Still not images of caterpillars that match yours. Perhaps one of our readers can find the answer.

Update: Caterpillar on Lupine: Twirler Moth Caterpillar??? (05/18/2007) ID caterpillar In regards to your posted photo, it looks like the caterpillar may be Pyralidae family, species: Uresiphita reversalis, which I have on my own website, http://www.colinlmiller.com/wildlife/lepidoptera/lepidoptera_caterpillars.htm.

Letter 2 – Caterpillar found in Snow in Alaska

Subject: Alaska bug care
Website:
March 21, 2016 12:50 am
My family is a new fan of your website, team, and especially Mr. Marlos! After coming across a cocooned caterpillar question that was nearly identical to our experience (Kenai peninsula, AK) a 5 hour drive from Anchorage, AK where the similar story took place 2 years ago very near the same period of season the other discovery was made.

I realized we have no understanding of how to care for this bug. I’m not convinced whether it made a cocoon in our Tupperware over night of if it simply has an interesting way of dying.

However I, too, am not a fan of killing bugs. So I’m hoping you may have information on how to provide care for this bug until it either erupts from it’s possible cocooned state. Or shows an undeniable death. Please feel free to contact us in any way!! We absolutely adore what you are doing with this site!! Sincerely,
Sheeara & Marshall Woodward
(Mom & 8 year old Son)
Soldotna, Ak 99669
(Just in case you want to google map is and see where this little guy came from or.. hint hint hint… Allow us to be honored by purchasing a signed copy of The Curious World of Bugs.
Signature: Sheeara Woodward

Dear Sheeara & Marshall,
After conversing with you yesterday, we were compelled to go back through our old emails to search for your request.  As you noted, Alaskan submissions to our site are relatively uncommon. 

We are happy to learn that you were eventually treated to the emergence of the adult “red moth” and since you have images, we would love to include them in our posting, and hopefully provide you with a species identification.  Please attach your images to this response.  We would be honored to sign a copy of The Curious World of Bugs if you send a copy our way.

Letter 3 – African Bollworm imported to UK

Sugar Snap Hitchhiker
Location:  Maidenhead, UK
August 18, 2010 7:19 am
Greetings from the rainy UK, where we have discovered a hitchhiker from sunnier climes, smuggled in by a large supermarket chain inside a Sugar Snap pea pod. Now a few days old and finishing his third set of peas, Claudio is doing well. Any ideas whether he will become more interesting when he pupates?
Wil Mohr

African Bollworm

Update:  Sugar Snap Hitchkiker
August 19, 2010
Hi Bugman, after further investigation, have found it appears to be the dull
and unspectacular African Bollworm – Helicoverpa armigera (Synonym:
Heliothis armigera)
http://www.infonet-biovision.org/default/ct/76/pests
best regards – wil

Hi Wil,
Thank you so much for taking the time to write back after you self-identified your African Bollworm, Helicoverpa armigera, also known as the Old World Bollworm.  The Center for Invasive Species and Ecosystem Health website provides this information:  “Old world bollworm is native to Europe and Asia. It is not known to be established in North America.

Possible routes for introduction include imported cuttings, fruits, vegetables, and flowers, as well as hitchhiking on aircraft. This species is a general feeder and is highly resistant to pesticides. Hosts include a wide variety of fruits, vegetables, weeds, ornamental plants, and flowers.

A partial list includes pine, larch, crab apple, artichoke, barley, carrot, coffee, mango, alfalfa, cotton, tobacco, tomatoes, okra, onion, peppers, leek, clover, potatoes, wheat, maize, flax, soybean, sorghum, rice, millet, lucerne, strawberry, chickpeas, crucifers, legumes, cucurbits, Prunus spp., citrus, Amaranth spp., and sow thistle. In summer, a life cycle can be completed in 5 to 7 weeks.

Following generations feed on other plantings of the same crop or on other hosts. One female moth may lay up to 1,500 eggs. The dome-like eggs have a ribbed surface and are pearly white when laid, but change to brown as they develop. The young caterpillars are predominantly green but the colors vary through development.

When mature, larvae may be up to 2 inches long and usually have striped patterns over a base color that ranges from light green to brown to black. Distinct hairs are visible when held up to the light.

Larval development takes 2 to 3 weeks before pupation occurs in the soil. The reddish-brown pupa stays in the soil for 10 to 14 days when not overwintering. Adults have light fawn forewings with a kidney-shaped spot in the middle. Hindwings are grey to grey-brown.

Both wings have a broad dark band on the outer third of the wing but the band on the hind wing has a pale patch in the middle of the dark band.

When resting, the wings are held roof-like over the body.“ In the UK, it is known as the Scarce Bordered Straw and the UK Moths website has this information:  “An immigrant species to Britain, mainly around the southern coasts, and occurring most often in the autumn months.
It is also found as a larva from time to time on tomato plants, geraniums and other plants brought in from the Mediterranean region, where it can be a pest.“

Letter 4 – Another Mystery Caterpillar

what’s this caterpillar?
Hi, I found this guy eating my petunias. I’ve never seen one quite like it so I refrained from smooshing it. I’m happy to share my plants if it is something cool. What is it? I live in Southern Oregon.

The caterpillar is approximately 1 inch long. It is a rosy red with a light pink or white stripe along both sides. Thank you,
Rebecca

Sorry Rebecca,
We don’t know what your caterpillar is. We suspect it is a butterfly and not a moth. It is a beautiful color, almost camoflauged on the petunias. You can raise it and see what emerges.

Letter 5 – Another Turbulent Phosphila Caterpillar

picture attached
OK, here is the picture of the caterpillar I described to you yesterday (from my dog’s head). I don’t know what kind of leaves it likes, it’s in a ventillated tupperware with some oak & maple leaves right now Hope you can identify it for me!
Bill

Hi Bill,
Several days ago we got a photo of a group of the same caterpillars. It took us awhile to identify the Turbulent Phosphila, Phosphila turbulenta. It feeds of Greenbriar leaves, Smilax.

Letter 6 – Army Worms

Worms?
Hi
I find these guys moving as a group with one or two white grub looking worms along with them. I see them at night or early morning on our sidewalk. They were moving in a circle the other night (pict below). I didn’t know to look under worms, grubs, or caterpillars. I live in southern Connecticut. Any help would be great.
Thanks
Chris

Hi Chris,
You have caterpillars known commonly as Army Worms. These are ravenous, very destructive moth larvae that live their early lives in groups, later dispersing as they grow. Here is a good site with addtional information.

Letter 7 – Blue Caterpillar

Caterpillar ID?
Hey Bugman!
I found this caterpillar enjoying my purple verbena. I looked on your website and Bug Guide, I couldn’t find it. I thought it might be a slug caterpillar because of its shape, but it doesn’t have stingers on it. It’s a mauve color and I tried to get a super clear photo of it, but I didn’t have much luck. I love your website. It’s the first one I check when I need to ID something. Thanks for all of your hard work!! Thanks!
Sheila H. Bragg
Rincon, GA

Hi Sheila,
Your caterpillar is one of the Gossamer Winged Butterflies in the family Lycaenidae, probably one of the Blues in the subfamily Polyommatinae. It looks quite close to a photo of the Ceraunus Blue caterpillar posted to BugGuide. The species is found in Georgia

Letter 8 – Caterpillar from Sumatra

Subject: Pseudosphinx in Sumatra ???
Location: West Sumatra – Indonesia
October 7, 2015 9:05 am
Hi,
I send you an other picture from my place (West Sumatra – Indonesia). The only one similar bug i found is a Pseudosphinx tetrio. But it can be found only in America and Carribean (according to articles that i found)… and i’m in Indonesia !!!
There are some small differences with pictures of P.tetrio that i found : no anal horn, black backhead (instead of orange), white long hair, extremity of feet orange-brown (instead of completely orange-red).
Also, the one on the picture is eating a plant that produces latex. But Pseudosphinx do not eat this kind of plant.
Thank you for your help
Greetings from Sumatra !
Signature: Nad Rimba

Unknown Caterpillar

Dear Nad,
This is most definitely NOT a Tetrio Sphinx Caterpillar, a species found in Central and South America, but we are uncertain of its identity.  We are posting your image and we will continue to research its identity.  This is also a gorgeous image.

Letter 9 – Caterpillar from South Africa

Subject: Unidentified Caterpillar
Location: Bloemfontein region, Free State, South Africa
March 31, 2014 10:24 am
Hi, I found this caterpillar on our Private Game Farm in the region of Bloemfontein, Free State, South Africa and am hoping you may be able to assist in it’s identification?
It’s an active night feeder, resting during the day .
Feeding on Quilted Bluebush (Diospyros lycioides).
Numerous groups have been contacted in regards to it’s identification, but as yet, no such luck.
Signature: Toby Esplin – About Nature, Wildlife and Birding Tours

Caterpillar

Dear Toby,
We don’t think we will have time to research this request this morning, but we are posting all of your images and perhaps one of our readers will be able to provide a response.  Our initial guess is that this is probably the caterpillar of a large moth in the family Erebidae because it reminds us of the Underwing Caterpillars from North America.

Caterpillar

Caterpillar

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