Overview
The Ten-lined June Beetle (Polyphylla decemlineata), affectionately known across the American West as the ‘Watermelon Beetle,’ is a colossal, charismatic scarab beetle famous for its bold pinstriped livery and its surprising ability to loudly hiss like an angry cat when picked up. Flying with a heavy, buzzing drone on warm summer evenings toward porch lights, adult males display extravagant, fan-like feathered antennae that resemble miniature golden moose antlers.
Biology and Physical Characteristics
Polyphylla decemlineata features a robust, heavy oval body clad in leathery dark brown or rusty-chestnut elytra (wing covers) decorated with ten crisp, chalk-white longitudinal stripes formed by dense microscopic scales. Males possess spectacular flabellate antennae tipped with seven large, flattened lamellae (plates) that open and close like miniature folding fans to detect female pheromones across vast distances.
Behavior and Ecology
Emerging from subterranean pupation during hot June and July evenings, adults fly clumsily through the canopy, feeding sparingly on conifer needles and deciduous leaves. When handled or threatened by birds, the beetle violently contracts its abdomen against its hard wing covers, forcing air out through its spiracles to generate an astonishingly loud, raspy squeaking hiss that startles predators into dropping it.
Conservation and Human Impact
While not formally assessed on the global IUCN Red List, the Ten-lined June Beetle is common and widely distributed across western North America. While its massive subterranean ‘white grub’ larvae can occasionally damage commercial apple orchards and berry root systems, adults are beloved nocturnal icons of western summer nights.
Interesting Factoid
When alarmed, the Ten-lined June Beetle defends itself by hissing loudly like an angry rattlesnake, vigorously contracting its abdomen to force compressed air out of its breathing holes to scare away curious predators.