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How to identify it
- Adults are about 1/2 inch long (9.5 to 13.5 mm) with a long, slender, parallel-sided body, dull yellow to reddish orange, and the tips of the wing covers are deep purple to black.[1][3]
- The antennae are long, about half the length of the body.[1]
- Larvae grow to slightly more than 1 inch long and make long, winding tunnels inside rotted wood.[1]
Look-alikes
Where it lives
Originally European and spread by commerce around the world; in North America it is most abundant along the coasts, especially the Northeast and the West Coast, but turns up wherever there is wet, rotting lumber.[3][1]
Biology and life cycle
Females lay their eggs on moist wood, and the larvae take about a year to develop as they tunnel and feed.[1][3]
Adults can emerge at any time of year but are most common from May through August in Iowa, while Ohio State gives March to July as typical for the Northern Hemisphere; the adults don't feed and live only about one to two weeks.[1][2][3]
Damage and signs
- Larval feeding speeds the decay of wood that stays continuously wet; along waterfronts the beetle damages pilings, wooden boats and waterfront buildings.[1][3]
- Indoor emergences usually trace back to wet wood: timbers or posts in contact with moist soil, wood under leaking plumbing, or old lumber buried under a slab; wood soaked by dog urine is reported to be especially attractive.[1][2]
Health risk
The beetles are a nuisance indoors; none of the sources reports bites, stings or other harm to people or pets.[1][2]
Control
Prevention
Fix the moisture problem and remove or replace the rotted wood, including decayed structural lumber and wood lying on or buried in the soil.[1]
Traps and physical control
Vacuum up or pick up and discard beetles that emerge indoors.[1]
Pesticides
Iowa State says insecticide sprays are not useful against this pest.[1]
Common questions
- Why are long orange beetles appearing at my windows?
- Slender, half-inch yellow-to-orange beetles with dark wing tips gathering at windows and lights are likely wharf borers emerging from wet, rotting wood somewhere in or under the house.[1][2]
- Do I need to spray for wharf borers?
- No; sprays don't help. Find and fix the wet, rotting wood they breed in, and vacuum up the beetles.[1]
Sources
- Iowa State University Extension and Outreach, “Wharf Borer (Yard and Garden encyclopedia, last reviewed July 2020).” yardandgarden.extension.iastate.edu/encyclopedia/wharf-borer (accessed 2026-10-17)
- Ohio State University Extension (Buckeye Yard & Garden onLine), “Wharf Borer Beetle (Nacerdes melanura L., Coleoptera: Oedemeridae).” bygl.osu.edu/node/2359 (accessed 2026-10-17)
- Smithsonian Environmental Research Center (National Exotic Marine and Estuarine Species Information System), “Nacerdes melanura (Wharf Borer) species summary (NEMESIS).” invasions.si.edu/nemesis/species_summary/-305 (accessed 2026-10-17)
- iNaturalist, “Nacerdes melanura taxon page (order and family).” www.inaturalist.org/taxa/225433 (accessed 2026-10-06)