10 Fascinating Facts About Caterpillars

Interesting Behaviors and Traits You Probably Never Knew

Monarch caterpillar eating milkweed
Adam Skowronski / Flickr / CC BY-ND 2.0

Surely you've seen a caterpillar in your lifetime, and you've probably even handled one, but how much do you know about Lepidopteran larvae? These cool facts about caterpillars will give you new respect for what remarkable creatures they are.

A Caterpillar Has Just One Job—to Eat

During the larval stage, the caterpillar must consume enough to sustain itself through its pupal stage and into adulthood. Without proper nutrition, it may not have the energy to complete its metamorphosis. Malnourished caterpillars may reach adulthood but be unable to produce eggs. Caterpillars can eat an enormous amount during a life cycle stage that typically lasts several weeks. Some consume 27,000 times their body weight during their lifetime.

Caterpillars Increase Their Body Mass by as Much as 1,000 Times or More

The larval stage of the life cycle is all about growth. Within the span of a few weeks, the caterpillar will grow exponentially. Because its cuticle, or skin, is only so pliable, the caterpillar will molt multiple times as it gains size and mass. The stage between molts is called an instar, and most caterpillars go through 5 to 6 instars before pupating. No wonder caterpillars consume so much food!

A Caterpillar's First Meal Is Usually Its Eggshell

In most cases, when a caterpillar ecloses (hatches) from its egg, it will consume the remainder of the shell. The outer layer of the egg, called the chorion, is rich in protein and provides the new larva with a nutritious start.

A Caterpillar Has as Many as 4,000 Muscles in Its Body

That's one seriously muscle-bound insect! By comparison, humans have just 650 muscles in a considerably larger body. The caterpillar's head capsule alone consists of 248 individual muscles. About 70 muscles control each body segment. Remarkably, each of the 4,000 muscles is innervated by one or two neurons. 

Caterpillars Have 12 Eyes

On each side of its head, a caterpillar has 6 tiny eyelets, called stemmata, arranged in a semi-circle. One of the 6 eyelets is usually offset a bit and located closer to the antennae. You would think an insect with 12 eyes would have excellent eyesight, but that's not the case. The stemmata serve merely to help the caterpillar differentiate between light and dark. If you watch a caterpillar, you'll notice it sometimes moves its head from side to side. This most likely helps it judge depth and distance as it navigates somewhat blindly.

Caterpillars Produce Silk

Using modified salivary glands along the sides of their mouth, caterpillars can produce silk as needed. Some caterpillars like gypsy moths disperse by "ballooning" from the treetops on a silken thread. Others such as eastern tent caterpillars or webworms construct silk tents in which they live communally. Bagworms use silk to join dead foliage together into a shelter. Caterpillars also use silk when they pupate, either to suspend a chrysalis or construct a cocoon.

Caterpillars Have 6 Legs, Just as Adult Butterflies or Moths Do

There are way more than 6 legs on most caterpillars you've seen, but most of those legs are false legs called prolegs, which help the caterpillar hold onto plant surfaces and allow it to climb. The 3 pairs of legs on the caterpillar's thoracic segments are the true legs, which it will retain into adulthood. A caterpillar may have up to 5 pairs of prolegs on its abdominal segments, usually including a terminal pair on the hind end. 

Caterpillars Move in a Wavelike Motion, From Back to Front

Caterpillars with a full complement of prolegs move in a fairly predictable motion. Usually, the caterpillar will first anchor itself using the terminal pair of prolegs and then reach forward with one pair of legs at a time, starting from the hind end. There's more going on than just leg action, though. The caterpillar's blood pressure changes as it moves forward, and its gut, which is basically a cylinder suspended inside its body, advances in sync with the head and rear end. Inchworms and loopers, which have fewer prolegs, move by pulling their hind ends forward in contact with the thorax and then extending their front half.

Caterpillars Get Creative When It Comes to Self Defense

Life at the bottom of the food chain can be tough, so caterpillars employ all kinds of strategies to avoid becoming a bird snack. Some caterpillars, such as the early instars of black swallowtails, look like bird droppings. Certain inchworms in the family Geometridae mimic twigs and bear markings that resemble leaf scars or bark.

Other caterpillars use the opposite strategy, making themselves visible with bright colors to advertise their toxicity. A few caterpillars, like the spicebush swallowtail, display large eyespots to deter birds from eating them. If you've ever tried to take a caterpillar from its host plant only to have it fall to the ground, you've observed it using thanatosis to thwart your efforts to collect it. A swallowtail caterpillar can be identified by its smelly osmeterium, a special defensive stink gland just behind the head.

Many Caterpillars Use the Toxins From Their Host Plants to Their Own Advantage

Caterpillars and plants co-evolve. Some host plants produce toxic or foul-tasting compounds meant to dissuade herbivores from munching their foliage, but many caterpillars can sequester the toxins in their bodies, effectively using these compounds to protect themselves from predators. The classic example of this is the monarch caterpillar and its host plant, milkweed. The monarch caterpillar ingests glycosides produced by the milkweed plant. These toxins remain within the monarch through adulthood, making the butterfly unpalatable to birds and other predators.

Additional References

View Article Sources
  1. Egan, James. 3000 Facts About Animals. Lulu Publishing Services, 2016.

  2. James, David G., editor. The Book of Caterpillars: A Life-Size Guide to Six Hundred Species from Around the World. The University of Chicago Press, 2017.

  3. Horn, David J. "Moths of Ohio Field Guide." Division of Wildlife: Ohio Department of Natural Resources, Oct. 2012.

  4. "What Is the Strongest Muscle in the Human Body?" Library of Congress.

  5. Holland, Mary. Naturally Curious Day by Day: A Photographic Field Guide and Daily Visit to the Forests, Fields, and Wetlands of Eastern North America. Stackpole Books, 2016.

  6. Trimmer, Barry A., et al. Caterpillar Locomotion: A New Model for Soft-Bodied Climbing and Burrowing Robots. Tufts University Biomimetic Devices Laboratory, 2006.

  7. Gilbert, Cole. "Form and Function of Stemmata in Larvae of Holometabolous Insects." Annual Review of Entomology, vol. 39, no. 1, pp. 323-349., Nov. 2003, doi:10.1146/annurev.en.39.010194.001543

  8. Lin, Huai-Ti, and Barry Trimmer. "Caterpillars Use the Substrate as Their External Skeleton: A Behavior Confirmation." Communicative and Integrative Biology, vol. 3, no. 5, 23 May 2010, pp. 471-474., doi:10.4161/cib.3.5.12560

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Hadley, Debbie. "10 Fascinating Facts About Caterpillars." ThoughtCo, Apr. 5, 2023, thoughtco.com/fascinating-facts-about-caterpillars-1968169. Hadley, Debbie. (2023, April 5). 10 Fascinating Facts About Caterpillars. Retrieved from https://www.thoughtco.com/fascinating-facts-about-caterpillars-1968169 Hadley, Debbie. "10 Fascinating Facts About Caterpillars." ThoughtCo. https://www.thoughtco.com/fascinating-facts-about-caterpillars-1968169 (accessed June 8, 2023).