Squash Vine Borer

The squash vine borer is a clearwing moth whose larval stage is a serious pest of squash, pumpkin, and related cucurbit vines in North American gardens. Unlike most moths, adults fly actively during the day and closely resemble a wasp, with a stout orange-and-black body and largely transparent forewings, an example of mimicry that likely helps deter predators.

Females lay eggs individually at the base of host vines, and the resulting larvae bore directly into the stem, where they feed concealed for several weeks. This hidden feeding inside the vine is what gives the species its common name and its reputation as a difficult garden pest to detect before damage is advanced.

The adult moth itself is a strong, fast flier often seen visiting flowers or hovering near cucurbit plantings on warm summer days, while the larval stage remains entirely hidden within host stems.

• Forewings narrow and metallic olive-brown to black; hindwings largely clear with dark veins and margins
• Abdomen orange with bold black spots or bands, and hind legs fringed with conspicuous orange-red hair-like scales
• Wingspan roughly 1–1.5 in (25–38 mm); body shape and coloring closely resemble a wasp
• Flies actively in daylight, unlike most moths
• Larva is a wrinkled, white to cream-colored caterpillar with a brown head, found only inside squash and pumpkin stems
• Sawdust-like frass pushed out of a small hole at the base of a wilting vine is the classic sign of larval infestation

Found across much of North America wherever squash, pumpkin, zucchini, and other cucurbit crops are grown, from home gardens to commercial fields. Adults are most active in early to mid-summer, coinciding with vine growth, and larvae are found inside stems through summer until they leave to pupate in soil.

Adult moths visit flowers for nectar and are frequently seen hovering or darting around cucurbit plants during the day while searching for egg-laying sites near the base of vines. Larvae tunnel through the interior of the stem, feeding on the pith and interior tissue, which can disrupt the vine's ability to move water and nutrients and cause sudden wilting of affected runners. As with many stem-boring caterpillars, this species plays a minor ecological role as prey for birds and parasitic wasps that target concealed larvae.

Development is complete metamorphosis. Eggs are laid singly on stems near the base of host plants and hatch in about a week; larvae then bore into the stem and feed internally for roughly four to six weeks before exiting to burrow into the soil, where they spin a cocoon and overwinter as a pupa. Adults emerge the following late spring or early summer, and depending on climate there may be one or two generations per year.