Adult geometrid moths have thin bodies and usually hold their wide wings spread flat out to the sides; a few species will hold their wings above their body in a “V,” like a butterfly. There is great diversity in the color, shape, and size of members in this huge moth family. Many have camouflage coloration and patterns, and the patterns on the forewings and hindwings are often matched so that when the moth is resting, the lines appear continuous across all four wings. Some species have pointed forewings and scalloped wing edges. Male geometrids have feathery antennae, while females have thin filaments. Some Missouri species have wingless females. Many geometrids have a fluttering flight.
Examples include the chickweed geometer, orange wing, wavy-lined emerald, spring and fall cankerworms, great bark geometer, and curve-toothed geometer.
The caterpillars of geometers (“earth measurers”) are the familiar inchworms that hump their backs (forming a “loop”) when they move the rear set of legs up to the front set, before moving the front set forward for the next “step.” Geometrid caterpillars lack several of the midbody legs found in most other moth families, which explains this mode of “walking.” Geometrid caterpillars are typically long and slender and have camouflage colors of green or brown plus bumpy patterns and rings that make them look exactly like tiny twigs. This mimicry is enhanced by their habit of resting in a slanted, stiff, straight, twiglike posture.
Similar species: Adult hooktip moths (family Drepanidae) hold their wings similarly, but they have hooks at the tips of their forewings. Some erebid moths (family Erebidae) have wing patterns that continue from the forewings onto the hindwings. Many species of pyralid moths (family Pyralidae) have the overall shape of geometrids, but the abdomen of pyralids frequently extends past the hindwings in a resting position, while the abdomen of most geometrids does not extend past the hindwings.
Not all “loopers” are geometrids. Some, like the cabbage, soybean, clover, bilobed, and celery looper moths, are in the noctuid family. Their caterpillars have the same method of “walking.”