Inching Along – Geometridae

An inchworm (family Geometridae) climbs flowers at the Welder Wildlife Refuge, in Texas

Inchworms (also called loopers and spanworms) are a type of caterpillar that take their name from their unique method of moving.  Rather than crawl along leg by leg, these caterpillars have adapted to take advantage of the length of their bodies and “inch” along, contracting the front and back portion of their bodies.  Even the placement of the prolegs (false extra appendages found in some insect larvae) has adapted to this behavior–inchworms lack prolegs in the middle of their body.  Inchworms are typically colored in greens or browns to blend into their environment.  Some, such as the caterpillar below, may have extra filaments to aid in their disguise.  Caterpillars may strike poses to resemble twigs, stems, or even bird poop!

A filament bearing geometrid on a plant stem (Flynn, TX).

The “inchworm” style of movement has independently evolved in several lineages of caterpillars.  However, by far the most abundant and diverse group are the caterpillars of the geometer moths, in the family Geometridae. This family name literally means “earth measurer” and these moths are often better known for their caterpillars than their adults.

Inchworm inching along.