Ornamental & Turf Insect Note Logo


James R. Baker, Extension Entomologist Emeritus

CAUTION: This information was developed for North Carolina and may not apply to other areas.

Prionoxystus robiniae (Peck), Cossidae, LEPIDOPTERA

General Information

drawing of mothCarpenterworm moths are dark, slightly mottled and have stout bodies. Females (wingspan of about 3 inches) are considerably larger than males. Male moths are dark and their hindwings have a large yellowish to orange spot with a black border. The egg is olive green, oblong and slightly larger than the head of a sewing pin. The surface of the egg has a minute network of ridges and shallow pits. Carpenterworms (larvae) are pink to greenish white and grow to 2 2/4 inches long. The pupae are dark brown and up to 2 inches long.


borer in galleryCarpenterworms are found across North Carolina. Shade trees such as ash, elm. maple, oak, poplar and willow are commonly infested. White oaks appear to be a favored host tree in North Carolina. Carpenterworms bore into the heartwood of trunks and limbs. They seldom kill trees outright, but small, heavily infested trees may break off in high winds. The greatest commercial damage results from degradation of lumber cut from infested trees. The overall value of rough-cut oak lumber may be reduced 15 percent. Yard trees or trees growing on poor sites such as dry ridge tops or ridge slopes seem to be particularly likely to be infested. Greater damage occurs when carpenter ants and woodknot fungi invade the tunnels.

The carpenterworm, a major pest of hardwood trees, was first described in 1818. The life cycle requires from 2 to 4 years, depending on geographic location. However, generations overlap in all areas of North Carolina, so one may find larvae in all stages of development at any time and moths in flight every year. In the South, moth emergence begins during late April, peaks in late May or early June and ends in early July. The moths emerge during daylight hours. Females usually emerge slightly earlier than males. Females produce a sex pheromone that attracts males. Females normally mate once, but males may mate 4 or more times.

The eggs are laid in groups of 2 to 6 or singly, and the number laid by each female varies from 200 to 1,000. Eggs hatch in 10 to 14 days. Newly hatched larvae feed for a short while on the empty egg shells, but within a few hours begin penetrating bark or entering openings. The number of larval instars (stages) varies from 8 to 15. Young larvae feed on the inner bark until about half grown. Then they bore into the wood making tunnels which angle upward in the sapwood and turn straight upward in the heartwood. Tunnels are kept open and enlarged by the growing carpenterworms. Eventually the tunnels may reach a diameter of 5/8 inch with a length of 12 inches.

Mature larvae line their tunnels with loose, silky, yellowish-brown webs. Pupation (duration of 17 to 19 days) occurs at the upper end of the tunnel. Mature pupae wiggle to the opening of the tunnel and protrude from the trunk. The adult soon emerges. The pupal skin remains protruding from the trunk until it weathers away.


Little is known about natural control of this insect. It is believed, however, that predation by woodpeckers on larvae and kingbirds on adults frequently accounts for the destruction of fairly large numbers. Insect parasitism appears to be inconsequential.

No satisfactory method of control in the forest is known, although the removal of heavily infested, weak, deformed, and cull trees should be helpful in reducing the intensity of the infestation. Shade trees can be protected by preparing and painting injuries with wound dressing.

Larvae can be killed by probing their tunnels with a wire. Fumigants such as ethyl acetate, acetone or other commercial preparations may be squirted into the tunnel with an oiler, then cover the exit hole plugged with putty or tree paint. Tests injecting parasitic nematodes (Steinernema carpocapsae) into tunnels showed good results.

Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
© 2001 NC Cooperative Extension Service
Prepared by: James R. Baker & S. B. Bambara, Extension Entomologists

August 1994 (Revised) May 2001

Web page last reviewed January, 2011 by the webperson.