Caterpillars are not the same as worms, despite often being confused as the same animal.
People tend to mistake caterpillars for worms because they look similar, while both are commonly found outside in gardens.
However, there are many differences between caterpillars and worms, which are easy to spot once you know what to look for.
The below guide covers all the info you need to know about the main differences – and a few similarities – between caterpillars and worms. (and if you typed up caterpillar vs worm expecting a fight, we have a video on that too!)
KEY TAKEAWAYS
- A caterpillar and a worm are different species
- While they have many similarities, they also have many differences such as their body segments, legs, head, movement, habitat, life cycles and more
- The confusion often comes from caterpillars or moth/butterfly/beetle larvae being given the name “worm”, for example, the Tomato Hornworm, mealworms or superworms
- Curious about who wins in a fight? We have a video in this article showing this too!
Is a Caterpillar a Worm?
No, a caterpillar is not the same species of animal as a worm.
Caterpillars are the larval stage of moths and butterflies, known as members of the Lepidoptera.
Of course, many caterpillar and worm species look similar, so it’s easy to see why they are often mistaken as the same type of animal or other animals of a similar nature.
Some species of caterpillars even have “worm” in their name and are called worms because their larval stage looks worm-like, only adding to the confusion!
For instance, the tomato hornworm and inchworm are both a type of caterpillar but have the term “worm” in their name.
Worms are various types of invertebrate animals that have long, cylindrical bodies.
Some of the most common examples of worms include segmented worms, flatworms, and roundworms.
What’s the Difference Between a Caterpillar and a Worm?
There are many differences between a caterpillar and a worm, although these are often difficult to notice to the untrained eye.
Because worms and caterpillars usually have similar-shaped bodies, they’re commonly mistaken as the same species.
Animal Kingdom
One of the main differences between a caterpillar and a worm is that they are two separate species of animals.
For example, caterpillars are insects, being the larval form of the order Lepidoptera.
This is an insect order comprising butterflies, moths and other creatures of a similar nature.
Earthworms aren’t classified as insects and don’t go through a larva stage.
Movement
Caterpillars have three pairs of legs.
An interesting aspect is that they only have six true legs which are their thoracic legs, located at the front of the body, just under the head, while the rest are leg-like parts (or “prolegs”), rather than actual jointed legs.
There’s an interesting theory on how they evolved these legs over time here.
They can use these legs to to climb plants and even trees. Somewhere you’d never find earthworms.
Worms lack legs or any type of limbs, as they don’t move in this way, instead stretching and contracting long or circular muscles to get around.
Diet: Mouth and Jaws
Caterpillars also have a true head with jaws and two small teeth like parts to their mouth (not teeth like humans have) which they use to eat leaves and feed on other native plants.
A worm doesn’t have teeth or a jaw, so doesn’t chew food as a caterpillar does, preferring to almost vacuum up tiny particles of organic matter that can fit into a worm’s mouth.
Caterpillars may even eat insects, dead or alive!
This is another difference, since worms feed exclusively on dead, organic matter (plants and animals).
Whereas a caterpillar is happy to eat plant matter that is very much alive and is an insect that can devastate some crops.
Body Segmentation
Caterpillars have a body that is often divided into at least 11 parts; these are made up of thoracic and abdominal segments.
The earthworm and most worms have a single, cylindrical part to their body made up of muscular segments for movement.
Life Cycles
Caterpillars and worms also have different life cycles.
For example, the worms you see are often in the adult stage of their life cycle. They go from egg to worm.
Caterpillars, on the other hand, are in the second stage of a multi-stage life cycle that goes –
- egg
- larvae
- pupa
- adult moths or butterflies
Eyes
Worms don’t have eyes, while caterpillars have multiple eyes, although these eyes only see changes in the light rather than forming any images.
Habitat
Most worms live in moist areas (this helps them breathe through their skin) beneath the soil or among the organic matter on the ground.
This allows them to eat small particles of decayed food or plant matter which has been absorbed by the soil.
Caterpillars vs Worms: Who Would Win in a Fight?
Want to see some of the above differences between these two animals in action?
If you searched this in Google expecting to see who would win in a fight, then we’ve got you covered here too.
Here’s a video of an earthworm vs a caterpillar. Knowing their differences, who do you think wins?
As expected, with the caterpillar having more tools for combat, like teeth and jaws, it wins pretty handily.
You may have noticed the 3 pairs of legs we mentioned, as well as the teeth, jaws and segmented body on the caterpillar.
The earthworm’s only way to protect itself was releasing fluid to try and escape the caterpillar’s grip, but this was futile.
What are the Similarities Between Caterpillar’s and Worm’s?
There are actually a few similarities between the worm and the caterpillar/caterpillars:
- Both have soft bodies
- Both are invertebrates
- Both are cold blooded species
- Both have “setae”, invisible bristles* which help with movement and heat retention
- Certain species of both can be considered “pests”
- Both have similar predators in birds, moles and other animals who eat worms, grubs or other larvae
- Both can carry parasites (though parasites are potentially more deadly to caterpillars and can take control of them – zombie apocalypse, anyone?)
*Some caterpillar species like the tent caterpillar will have visible bristles covering their soft bodies.
Are There Worms that Look Like Caterpillars?
At a quick look, it’s easy to think that some worms look like caterpillars.
For instance, both types of animals have similarly shaped bodies and are usually found wriggling around outside, though many worms tend to stay underground and live beneath the soil (besides the surface-dwelling worms like red wigglers)
However, upon closer inspection, it’s clear that worms don’t look like caterpillars.
As mentioned above, there are many physical differences between caterpillars and worms.
Caterpillar’s legs, eyes, and their jaws with teeth which gives them a more complex chewing apparatus than the worm, are some clear differences.
Does a Worm Turn into a Caterpillar?
No, a worm does not turn into a caterpillar.
The reason some people think that a worm turns into a caterpillar is because of the unique multi-stage life cycle of a caterpillar.
For instance, a caterpillar is currently in its second stage, having started life as an egg laid by a butterfly or a moth, depending on the species.
Once the caterpillar has fully grown, it enters a third stage where it becomes a pupa, also known as a chrysalis.
After the pupal stage, the caterpillar emerges from its pupa as a fully grown butterfly or moth.
Worms are born from eggs, growing from hatchlings into adults after a few months.
How to Know What You’re Seeing is a Caterpillar or Worm?
Because both caterpillars and worms are animals with similar appearances, telling the difference between each one is sometimes challenging.
Thankfully, it’s easy enough to spot the differences between each animal once you know what to look out for.
One of the first indicators that you’re looking at a caterpillar is that it has legs.
As previously mentioned, worms don’t have any legs, while caterpillars have legs across multiple sets of thorax or prolegs.
So, look at the animal for signs of legs, with most species of caterpillar having between five to eight pairs of legs across their body.
Another way to tell if you’re looking at a caterpillar or worm is by inspecting its head.
Worms do have heads, but these aren’t as obvious compared to caterpillar heads, which have a set of eyes.
Also, look for a head with jaws, as caterpillars have pronounced mouthparts for eating.
Another factor to consider when looking at the animal is the general tone of its skin.
Most caterpillars have bright-colored skin, often featuring stripes and spots of varying colors.
The reason that caterpillars are so vibrant is to help ward off predators – these colors warn animals not to the eat them because the caterpillar is toxic.
Worms lack bright pigmentation, so are usually colorless or very pale.
Summary
Despite what many people believe, caterpillars and worms are completely different animals.
Caterpillars are usually moth larvae or the larvae of butterflies, while worms aren’t even classed as insects.
While there are some similarities between worms and caterpillars, such as their cylindrical bodies, soft flesh, and wriggly movements, there are many ways to tell them apart.
Many caterpillars have legs, eyes, teeth, and bright skin, while worms lack all these features and a generally pale or colorless.
Caterpillars also live multi-stage life cycles, being born from eggs before changing from their larval stage into a pupa and eventually caterpillars hatch (more like “turn”) into a butterfly or moth.
Worms begin life as eggs, emerging as hatchlings before maturing into adults in a few months.
Both animals are great for the environment, playing a vital role in our ecosystems.
So, next time you spot a small, wriggly animal in your garden, make sure to take a closer look to see if you can spot the difference between caterpillars and worms!
REFERENCES
Williamson DI. Caterpillars evolved from onychophorans by hybridogenesis. Proc Natl Acad Sci U S A. 2009 Nov 24;106(47):19901-5. doi: 10.1073/pnas.0908357106. Epub 2009 Aug 28. PMID: 19717430; PMCID: PMC2785264.
