Elm Leaf Beetle

The elm leaf beetle (Chrysomelidae) is a 6–8 mm oblong beetle, yellowish-green to olive with a black longitudinal stripe along each elytral margin and three dark spots on the pronotum; overwintering adults fade to a dull olive-brown. Females lay yellow-orange eggs in double rows of 5–25 on the underside of elm leaves, laying several hundred over a season. Larvae are black-striped, yellowish, grub-like, and feed for 2–3 weeks through three instars before pupating in bark crevices or at the tree base. One to three generations occur per year depending on climate, with adults overwintering in sheltered, dry sites — very often inside buildings.

Adults are diurnal and fly readily on warm days, dispersing between elm hosts. Larvae skeletonise leaves, feeding on the lower surface and leaving the veins and upper epidermis intact, giving the characteristic lacy bronzed canopy; adults chew clean shot-holes straight through the blade. Repeated defoliation stresses elms and predisposes them to bark beetle attack and Dutch elm disease. Indoors the beetles neither bite, feed, nor breed — they are a pure nuisance and staining problem, aggregating in wall voids, attics, and window channels, then reappearing at windows on warm winter afternoons and again during spring emergence.