If you have ever mistaken a caterpillar for a worm or vice versa, you’re not alone. At different stages, worms and caterpillars have many similarities. At the same time, at different stages, worms and caterpillars have many differences. For starters, both worms and caterpillars have soft bodies, meaning they do not have a skeletal system. Both animals are nocturnal as well. Depending on the species of worm, some caterpillars and worms may also be similar in length. Some caterpillars even grow up to three inches or more.
There are thousands of different species of worms and more than 2,700 species of earthworm alone. Like earthworms (annelida), caterpillars have segmented bodies. Another similarity between caterpillars and worms is caterpillars and worms are a favorite food for other animals. They are both protein rich and some worms, such as the white worm or “pasta worm”, are raised specifically for feeding to other animals such as fish. Worms and caterpillars are known for having hearty appetites. Their appetites are so hearty that they have earned the name “pest” by farmers around the globe. Depending on the type of worm or caterpillar, they can eat through crops of all kinds, plants, trash, and even inedible materials such as cotton.
Worms and caterpillars have to defend themselves against a wide variety of predators quite regularly. Because of this, each animal has no choice but to utilize a wide variety of techniques to ward off attacks. Worms protect themselves in several ways. If their attackers hunt for them below ground, worms will quickly withdraw into their burrows. If a worm finds itself face to face with a predator on the surface, the worm will thrash about, jump, and twist their bodies. Some worms may also spit and spew a foul smelling or foul tasting fluid.
The caterpillar is just as aggressive when it comes to defending itself. Caterpillars have long hairs or bristles on their bodies, which can detach and lodge into the skin or mucous membranes of the predator. In some caterpillars, the bristles contain poison from the caterpillar’s venom glands. This poison is so powerful that in the case of the South American silk moth, it can be fatal to human beings. Much like worms, caterpillars also spit juices and produce bad smells to ward off attackers. Caterpillars also have the ability to create a silk line and drop out of site if a predator approaches.
One of the most obvious differences between caterpillars and worms is caterpillars move around on three pairs of legs, while worms have no limbs at all. Worms move around by contracting their segments. Each segment has two pairs of hairs called setae. The setae help worms grip the soil or other materials. In general, worms and caterpillars move slowly. When faced by an attacker, however, they can move fairly quickly.