Wharf Borer

wharf borer beetle is one-half inch long, tannish-brown with dark wing tips
Photo by M. O'Donnell and A. Cline, USDA APHIS PPQ, Bugwood.org

Description of wharf borers

As the name implies, the wharf borer (Nacerdes melanura ) is common in the pilings and timbers of wharves, piers, and docks and is most abundant along the coastal areas of the U.S. However, it is found in any wet, rotting lumber and is distributed throughout the country. The wharf borer is only an occasional pest of rotting timbers in Iowa.

Wharf borer larvae may be found inside rotted timbers, though most reports originate when adult beetles emerge in the house.  The adult beetles are attracted to windows and lights.  Wharf borer beetles are one-half inch long with a long, slender, parallel-sided body.  Their color varies from dull yellow to reddish-orange with the tips of the wing covers deep purple to black. Like many of the other wood-boring beetles, the wharf borer has long antennae that are about half the length of the body.

Damage caused by wharf borers

Wharf borer beetles can emerge from infested wood any time of the year but are most common in May through August. The females lay their eggs on the moist wood, and the larvae tunnel into the wood. They feed and grow and produce long, winding tunnels inside the rotted wood. Larvae grow till slightly more than 1 inch in length. The feeding action of the borers promotes the wood decay that occurs because the wood is continuously wet.

Any wet, rotting wood could be a source for wharf borers. Reported sources include timbers and posts in contact with moist soil, lumber, or wooden items under leaking plumbing or other water problems and buried lumber. Wood wetted by dog urine is reported to be especially attractive to wharf borer beetles.

Management of wharf borers

Control of a wharf borer problem requires correcting moisture problems and removing or replacing rotted wood such as decayed structural lumber or wood laying on or buried in the soil. Insecticide sprays are not useful for the control of this pest, and their application would be a waste of time. Emerged beetles need only be vacuumed or picked up and discarded.

Last reviewed:
July 2020

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