What Do Inchworms Turn Into?

Quick Take

• The name inchworm has nothing to do with their size, and knowing the real reason they're called that will change how you see them move. Discover the naming truth →
• Inchworms move the way they do because of a body feature most caterpillars don't share, and that feature is stranger than you'd expect. See how inchworms move →
• The moths inchworms become look nothing like the plain little crawlers they started as. See the adult moth →
• Most people assume inchworms are a single species, but the actual number will catch you off guard. Explore the species count →

Tiny green or yellow worms known as inchworms pop up all over the place in the springtime. Technically, inchworms are little caterpillars that metamorphose into many types of moths within the family Geometridae. These little caterpillars have many nicknames, including inchworms, loopers, and measuring worms, inspired by how they move. Because they lack legs in the middle of their bodies, inchworms move by anchoring their hind legs, stretching their front half forward, and then pulling their rear end up, creating a distinct, repeating loop. Continue reading to learn more about these fascinating caterpillars.

What is a caterpillar?

Caterpillars are the larval stage of insects in the order Lepidoptera (which includes butterflies and moths). Their primary evolutionary purpose is to consume large amounts of vegetation and grow rapidly before transitioning into the pupal stage, during which they are encased in a chrysalis (for butterflies) or a cocoon (for moths).

Caterpillars are highly adaptable and thrive on every continent except Antarctica. Because they rely on vegetation for food, their distribution is closely tied to plant availability. While the vast majority of caterpillars are herbivores that feed on the foliage, stems, or seeds of specific host plants, a small fraction are carnivorous and eat other insects.

After completing their larval stage, caterpillars undergo metamorphosis and emerge as adult insects. Moths account for about 90% of Lepidoptera, with an estimated 160,000 described species. Butterflies make up the remaining 10%, with approximately 17,500 known species.

Caterpillars typically have a segmented cylindrical body, three pairs of true thoracic legs, and several pairs of fleshy prolegs, which are stubby legs with tiny hooks used for gripping.

What is an Inchworm?

Caterpillars in the family Geometridae are highly distinct in how they move. More traditional caterpillars move with an undulating, wave-like crawl using legs spaced evenly along their bodies. Geometrid caterpillars move by anchoring their front legs, arching their back into a high loop to bring their rear end forward, then anchoring their rear prolegs and stretching their front end out again. This makes them look like they are meticulously measuring the ground inch by inch.

There are approximately 24,000 described species of geometer moths worldwide whose larvae are true inchworms, with about 1,400 to 1,500 species found in North America

Although the nickname inchworm suggests that these caterpillars are small, it actually refers to their unique inching movement rather than their size. In fact, very few species of inchworms are actually one inch long. Some species are much less than one inch long, while others are over two inches long.

What do Inchworm Moths Look Like?

Once the inchworms have pupated and metamorphosed, they emerge as moths. Geometer moths have thin torsos and wide wings, usually held flat out to the sides.

Geometer moths come in many colors, shapes, and sizes. Camouflage patterns are frequently seen in colors of green, brown, white, and gray.

Geometer moths get their name from the Greek word for earth-measurer.