How to Manage Pests
Pests of Homes, Structures, People, and Pets
The names “wood wasp” and “horntail” describe several kinds of wood-boring insects in the order Hymenoptera, family Siricidae. Of greatest concern are the large, nonstinging wasps that normally are attracted to and complete their life cycles in newly dead or dying conifer trees. Timber salvaged from these trees can be processed into infested lumber. This can lead to adult wasps emerging in recently completed buildings or structures.
Although these insects are extremely annoying, they aren’t harmful to humans or structures. They attack only trees and won’t bore into wood in buildings or furniture. See the Pest Note: Wood-boring Beetles in the Home for information on borers that will attack furniture or structures.
The male and female have a similar body shape, except the female is larger and has a long egg-laying apparatus (ovipositor) that can exceed her body length. The female can use her ovipositor only for egg laying; she can’t use it to sting in defense. Although these pests can chew through wood, they don’t bite people.
Eggs hatch in 3 to 4 weeks, and larvae tunnel into the fungus-predigested wood parallel with the grain. Larvae are legless, cylindrical, whitish, and have a spine at the tip of their last abdominal segment. As they chew, larvae use a spine at the tip of their abdomen to help push themselves forward, through the wood. Larvae begin eating the softer wood (sapwood) just beneath the bark, following the fungus into the heartwood, then return to the sapwood to complete their feeding.
Larval feeding continues through 5 or more immature stages, which take at least a year and as many as 5 years in cooler climates to complete. The tunnel, or gallery, usually measures 10 to 12 inches long at completion.
Pupation takes place at the end of the gallery. After 5 or 6 weeks as a pupa, the adult emerges by chewing through about 3/4 inch of wood, leaving a round exit hole 1/4 to 1/2 inch in diameter.
Wood wasps don’t reinfest structures. Even if male and female wood wasps had the opportunity to mate in the building, the females would not be stimulated to lay eggs in dry, finished lumber.
Even though wood wasps can be a noisy, and sometimes scary, nuisance, they aren’t a threat to anyone or anything. Waiting out the life cycle and repairing cosmetic damage is about all that can be done in an infested building.
Ebeling, W. 1975. Woodwasps. In Urban Entomology. Berkeley: Univ. of Calif. Press. pp. 202–209.
Furniss, R. L., and V. M. Carolin. 1977. Family Siricidae–Horntails. In Western Forest Insects. Washington D.C.: U.S. Dept. Agric. Forest Service Misc. Publ. No. 1339. pp. 453–457.
Mallis, A. 2004. Handbook of Pest Control. 9th ed. Cleveland: GIE Media Inc.
Moore, H. B., and M. I. Haverty. 1979. Insects injurious to unfinished and finished wood in use. In J. A. Rudinsky, ed. Forest Insect Survey and Control. Corvallis: Ore. State Univ. Book Stores Inc. pp. 337–340.
UC Statewide IPM Program. Nov. 2000. Pest Notes: Wood-boring Beetles in Homes. Oakland: Univ. Calif. Div. Agric. Nat. Res. Publ. 7418.
Pest Notes: Wood Wasps and Horntails
Author: E. C. Mussen, Entomology, UC Davis
Technical Editor: M. L. Flint
Produced by University of California Statewide IPM Program
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