Squash Beetle

The squash beetle is one of the few plant-eating members of the ladybird beetle family (Coccinellidae), a family otherwise best known for predatory species that eat aphids and scale insects. It belongs to the subfamily Epilachninae, a small group of herbivorous lady beetles that specialize in feeding on cucurbit vines and a few other plants.

Its dome-shaped body and bold black spots on a yellow-orange to coppery background give it a superficial resemblance to a beneficial ladybird, which can be misleading in the garden since this species is a leaf-feeder rather than a predator. Adults and larvae both chew distinctive circular feeding patterns into squash, pumpkin, and cucumber leaves.

As one of relatively few phytophagous coccinellids in North America, the squash beetle offers an interesting counterpoint to the predatory reputation most people associate with lady beetles, illustrating the ecological diversity within a single beetle family.

• Adult: 7–10 mm, large and strongly domed like a classic ladybird, but colored coppery-orange to yellow-brown with roughly 14 large black spots arranged across the elytra.
• Body surface has a fine, fuzzy texture compared to the smooth, shiny shell of predatory lady beetles.
• Larvae are pale yellow and covered in branched, spiny projections, quite different from the smooth alligator-shaped larvae of predatory ladybirds.
• Lookalikes: easily mistaken for the beneficial spotted lady beetle, but the squash beetle is larger, duller, and always found actively chewing cucurbit leaves rather than hunting aphids.

Occurs in home vegetable gardens, farm fields, and open weedy areas throughout much of the eastern and central United States wherever squash, pumpkins, melons, and other cucurbit vines are grown. Adults and larvae are active from late spring through late summer, feeding on the host plant's foliage during the growing season.

Both adults and larvae feed on the leaves of squash, pumpkin, and other cucurbit vines, often chewing circular trenches around a feeding area before consuming the leaf tissue within, a behavior thought to interrupt the plant's defensive latex flow. This skeletonizing feeding pattern can leave leaves looking lace-like. As a specialist herbivore, the squash beetle plays a role in the natural pruning of wild cucurbit vines and is regarded as an occasional garden pest of cultivated squash.

Adults overwinter in garden debris or leaf litter and emerge in late spring to feed and mate. Females lay clusters of yellow eggs on the undersides of cucurbit leaves, which hatch into spiny larvae within about a week. Larvae pass through several molts while feeding on foliage, then pupate attached to the underside of a leaf. New adults emerge within a couple of weeks, and the species typically produces one to two generations per year depending on climate.