Ten-Lined June Beetle

Polyphylla decemlineata — the ten-lined June beetle — is the largest scarab beetle (family Scarabaeidae) in western North America and one of the most spectacular beetles of the Pacific Northwest and California. Adults reach 30-35 mm in length with characteristic ten cream-white longitudinal stripes on a dark brown background across the elytra (the source of the species name 'decemlineata,' meaning 'ten-lined'). Males are distinctively-antennaed: each antenna terminates in a fan-like cluster of 7 large feathered lamellae used for detecting female pheromones from substantial distances. Females have similar but less dramatic antennae. The species' most behaviorally unusual feature is the audible squeaking defense: when grabbed by a predator (or human), the beetle rubs the rear of the abdomen against a ridge on the underside of the elytra to produce a piercing audible squeak that startles the predator into releasing her. The sound is loud enough to be heard from several meters away. Adults are nocturnal, attracted to lights, and emerge in late spring/early summer (the 'June beetle' name). They feed on the foliage of conifers (pine, fir) and other trees. Larvae ('white grubs') develop over 3 years in soil, feeding on the roots of fruit trees, ornamental shrubs, vegetable garden plants, and turf grass — making the species a significant agricultural pest of stone fruit orchards and specialty crops in California and the Pacific Northwest. The species is a familiar sight on summer porch lights across the Pacific Northwest and a continuing topic of orchard pest management.