The term “potato bug” is often confusing, as it refers to several unrelated insects with varied sizes. Understanding these distinctions clarifies their actual dimensions.
The Colorado Potato Beetle: A Common “Potato Bug”
The Colorado Potato Beetle, Leptinotarsa decemlineata, is perhaps the most widely recognized insect associated with the “potato bug” moniker, particularly in agricultural regions. Adult Colorado Potato Beetles typically measure between 6 and 11 millimeters (0.24 to 0.43 inches) in length and 3 to 7 millimeters (0.12 to 0.28 inches) in width. They have a distinctive appearance with an orange-yellow body and ten prominent black stripes running lengthwise on their wing covers, or elytra. This beetle’s size is comparable to a ladybug but is often slightly larger and more elongated. Its rounded, convex body gives it a stout appearance.
Other Insects Commonly Called “Potato Bugs”
Beyond the Colorado Potato Beetle, other invertebrates are frequently misidentified as “potato bugs,” and these vary significantly in size. Sowbugs (Porcellio spp.) and pillbugs (Armadillidium spp.), which are terrestrial crustaceans rather than insects, are commonly called “potato bugs” due to their habit of being found in damp, decaying organic matter, including near potatoes. Adult sowbugs and pillbugs generally range from 6 to 19 millimeters (0.24 to 0.75 inches) in length. Pillbugs, like Armadillidium vulgare, are known for their ability to roll into a tight ball when disturbed, a behavior that gives them the nickname “roly-polies,” and can reach up to 18 millimeters (0.71 inches). Sowbugs, however, possess two small tail-like appendages and cannot fully roll into a ball.
Jerusalem Crickets (Stenopelmatus and Ammopelmatus genera), sometimes called “potato bugs” in Western North America, are much larger. These flightless insects can grow to be between 30 and 76 millimeters (1.2 to 3 inches) long. Their substantial size, coupled with a large, bald, humanoid head and a plump, banded abdomen, makes them distinct from the smaller Colorado Potato Beetle and isopods. Despite their common name, Jerusalem Crickets are not true crickets and are often found underground, feeding on roots and tubers.
Size Development Across Life Stages
The size of these “potato bugs” changes throughout their life cycles. For the Colorado Potato Beetle, the life cycle begins with small, yellow to orange, elongated eggs, 1 millimeter (0.04 inches) long, laid in clusters on the underside of leaves. These eggs hatch into larvae, which undergo four growth stages, or instars. First instar larvae are tiny, measuring 1.5 to 2 millimeters (0.06 to 0.08 inches) long. They grow, with fourth instar larvae reaching 8 to 15 millimeters (0.31 to 0.59 inches) long, appearing reddish-brown with black spots, before burrowing into the soil to pupate and emerging as adult beetles.
Sowbugs and pillbugs also grow through several stages, though their development is simpler. Females carry their eggs in a pouch, or marsupium, on their underside. Young sowbugs and pillbugs hatch resembling miniature adults, growing larger with each molt. They develop into adults within a year, reaching their full size and continuing to grow slightly throughout their lifespan, which can be up to three years.
Jerusalem Crickets hatch from eggs into nymphs, which look like smaller versions of the adults. These nymphs undergo multiple molts, increasing in size with each one, before reaching their full adult dimensions, a process that can take up to two years.