Common Name: Wharf Borer
Scientific Name: Nacerdes Melanura Nacerdes Melanura
The common name comes from the fact that the larvae bore into wharf pilings, both in sea water and fresh water. Adults are nuisance pests, especially when they suddenly appear in large numbers. This species is distributed worldwide.
Adults about 1/4-9/16″ (7-14 mm) long; body elongate, slender, and soft. Color of dorsum pale brownish/reddish yellow with elytral tips and sometimes pronotal sides blackish, eyes and venter black, antenna pale, and legs mostly dark. Antenna threadlike, about half of body length, and 12- segmented in males and 11 segmented in females. Pronotum with sides rounded (no lateral margins), widest at front, narrower than elytra at base.
Elytra each with 3 or 4 fine longitudinal ridges. Tarsi 5-5-4. Mature larvae about 1/2-1 3/16″ (12-30 mm) long; body elongate, parallel- sided, straight, and subcylindrical; color grayish white except for yellowish head and blackish mouthparts; dorsum of prothorax, mesothorax, metathorax, and abdominal segments 1 and 2 each with paired fleshy domelike protuberance covered with short spinules, abdominal segments 3 and 4 with paired ventral proleglike protuberances (ampullae) covered with short tooth like structures (asperities); surface smooth, with moderate number of scattered hairs/setae.
(1) Soldier beetles (Cantharidae) with pronotum margined, tarsi 5-5-5, and if yellow with black marks on elytra, then black mark also on pronotal dorsum.
(2) Blister beetles (Meloidae) with head broad, usually wider than pronotum, and a narrower neck.
(3) Long-horned beetles (Cerambycidae) with tarsi apparently 4-4-4, actually 5-5-5, and pronotum often widest at base.
(4) False Long-horned beetles (Cephaloidae) with claws comblike and pronotum widest at base.
The larvae typically bore in very moist wood in which fungal decay has already started. They do not bore a system of tunnels and galleries, but instead tend to work in rather indeterminate spaces which are plugged here and there with long torn wood fibers. These boring spaces are often adjacent to sound wood. The wood area being attacked cannot have a wood moisture content much above the fiber saturation point of about 30%.
Larvae can significantly accelerate the destruction of wood already attacked by fungal decay. Typically the first visible sign of infestation is the appearance of numerous adults. Quite often the infested wood is buried and not accessible.
Little has been published on the biology of this species other than the information given in the Damage and Signs of Infestation and Habits sections; descriptions of the larva and pupa have been published.
See the Damage and Signs of Infestation section above. Wharf borers attack mainly softwood but occasionally oak and other hardwoods are infested. This wood must be damp or wet and fungal decay must already have started. The moisture can come from either sea water or fresh water. Most commonly attacked are wharf pilings and timbers and wooden harbor and dock structures along coastal areas and inland waterways. Larvae are found in such wood at the high-tide mark and/or between the flooding and high-water level. They are also a problem in the hulls of wooden water craft, such as barges and sailing boats.
Around structures, wharf borers may occur in decaying moist wood found in foundation pilings under buildings, in damp basements and/or crawl spaces, wood around leaky plumbing, in buried wood, and in wood with ground contact such as old form boards and support posts.The senior author has encountered emerging adults in Virginia which were coming into a dental office from a damp crawl space.
In Chicago, they were entering through expansion joints into office space located in a converted sub-basement area of a major museum built on fill on the lakefront. In both cases, adults appeared annually in the late spring and summer for several weeks.
If possible, correct the excessive moisture conditions and remove all wood- to-ground contact, cellulose debris, and buried wood associated with structures. Spot treatment of non-removable buried wood with a pesticide labeled for wood-destroying insects may be helpful. Seal all possible entrances to problem rooms at the ground level. Remove the adults with a vacuum. Around docks and wharfs, replace decaying wood with pressure-treated wood. For water craft, replace the decaying wood and increase the frequency of hull inspection/maintenance.