University Cooperative Extension

no. 5.563

Firewood and house log insects in Colorado

David A. Leatherman and Whitney S. Cranshaw1

Quick Facts With few exceptions, insects found in fire- wood will not infest household furnish- ings. The best way to avoid insects emerging in the home is to store wood outdoors until needed. Some bark beetles in firewood, such as the Figure 1: Typical longhorned beetle (left) and mountain pine beetle and elm bark metallic wood borer (right). beetle, can infest nearby healthy trees. Well-dried wood is not favorable to bark Common Firewood and House Log Insects beetle survival. Wood borers—Wood borers are the most fre- quently observed insects infesting firewood and house logs. Most common are roundheaded borers You hear munching sounds in your firewood (Cerambycidae), also known as longhorned bor- or walls. Piles of white sawdust accumulate beneath ers or sawyers. Adult stage is a medium to large the wood. Sound familiar? beetle (1/4-2 inches), often with long antennae that Primarily from these initial symptoms, Colo- may exceed the body length. Roundheaded borers rado's wood boring insects are discovered and can are gray-brown with black speckling (sawyers) be a common cause of concern. or deep blue-black (black-homed pine borer). Adult Hundreds of insect species potentially can flatheaded borers (Buprestidae), also called metal- inhabit the wood of our native and ornamental lic wood borers, generally are smaller than round- trees. However, the great majority of cases involve headed borers. Flatheaded borers commonly are a few basic groups: roundheaded and flatheaded gray, bronze or blue-green with a metallic sheen wood borers; bark beetles; carpenter ants; and and have inconspicuous antennae. powderpost and anobiid beetles. Borer larvae are slender, white, segmented With few exceptions insects found within grubs with brownish heads and rather prominent Colorado firewood will not survive indoors and jaws. These larvae produce the chewing noises are only capable of infesting well-dried logs with and piles of wood-colored sawdust that frequently intact bark. The primary problems with firewood cause alarm. This sawdust material may be rela- insects involve a few species of bark beetles that tively fine or coarse and fibrous. These borers can develop in firewood and later infest healthy also are responsible for the wide zig-sag or mean- trees. By far, the most important of these insects is the mountain pine beetle, which kills large numbers of trees (primarily ponderosa pine) in 'David A. Leatherman, entomologist, Colorado natural forest areas. Elm bark beetles and, rarely, State Forest Service; and Whitney S. Cransbaw, Ips beetles also may threaten healthy trees after Colorado State University Cooperative Extension emerging from firewood. Simple precautions can entomologist and associate professor, entomol- prevent injury by these firewood insects. ogy (11/89) dering' tunnels seenbeneath the bark and deep in in firewood to quickly dry out and die. (Note: Colo- the wood. Thetunnel sof both groups are oval in rado termites do pot produce sawdust!) cross-section, not perfectly round. Wood borersare primarily a nuisance. The Control termites and, thus, disconcerting. Because of their Firewood insects do not normally pose any hazards to humans, household furnishings or long life cycle, borers may be present in wood for plants. This is particularly true for the wood bor- a year or longer. They do not emerge and attack healthy trees. No Westerners, species the most normally conspicuous recy- group of firewood in- cle in the same wood that produced them. Furni- sects.It is hard to witnes s the activity of borers withoutfeeling a need to tak e action, but in reality ture, wall framing or other seasoned woods are not suitable for wood borer attack. Despite pro- borersspeed up the dryin g process and promote ducing what may seem like great quantities of

dust, borers rarely tunnel extensively enough to Problemswith firewood insects emerging i n cause structural failure. Adult borers found inside the hom are best handled by storing firewood the home may look ominous and pinch theskin if outdoors until needed. Outdoor storage will greatly handled but are not dangerous. slow insect development during the winter and Bark beetles - Bark beetles (Scolytidae) com- limit the opportunity of insects to emerge inside a monly infest dead or dying trees and then appear home. The occasional insects that do manage to infirewood produced fro m such trees. For infor- emerge indoors can be controlled by vacuuming. Storing wood in a manner that accelerates mation on several well-known tree killers and dis- easevectors such as the mountain pin e beetle drying also is important in limiting firewood (SIA 5.528), European elm bark beetle (SIA insect infestations. Stack wood so that air readily 5.506) and Ips beetles (SIA 5.558), Adult bark beeflows- through the pile. Well-dried wood will not caninvite kill bark many beetle developing attack, barkand the beetle drying larvae process if tles are small (1/16-1/4 inch), dark and bluntly cylindrical. Infestation by the various bark bee- tleson conifers usually is marked by a glob of already present in the wood. pitch (pitch-tube) at the point of attack. Eggs are When collected firewood is known to harbor laid in central pathways (egg galleries) constructed mountain pine beetle or other undesireable spe- under the bark and the larvae feed on wood as they cies, the best option is to burn the wood before chew at right angles from the central gallery. adult beetles emerge. Outdoors, mountain pine Most bark beetles have a one-year life cycle, but a beetles begin to emerge in mid-July; elm bark bee- few can complete generations in two-month in- tles emerge from elm logs in mid-May. To avoid tervals. Bark beetles cannot reproduce in house- wood infested by these insects, choose trees for holdwoo dproducts. cutting that have been dried for at least one year Powderpost and Anobiid Beetles - Powderpost or that have noticeably loose bark. (Lyctidae) and Anobiid (Anobiidae) beetle infes- If log piles are small and located in a sunny tations of structural wood and furniture are un-area firewood insects can be killed by covering the pile with a clear plastic tarp. The high temper- common in Colorado but can be serious. Native atures produced will kill many insects inside the species of these insects do occur naturally in dead tree limbs and dry, seasoned wood. However, wood. Control of insects in logs at the pile's top may exceed 50 percent, but insects in lower logs problems with these insects in Colorado appear to be associated with the introduction of infested generally are not affected. A more difficult, but highly effective means of wood products from Eastern states. Fresh piles of fine sawdust and small round holes (1/32-1/8 inch killing most firewood insects is to remove the diameter) are possible signs of infestation. bark. Debarking also will prevent reinfestation Carpenter ants—Intact, sound logs are not and speeds drying. used by carpenter ants (Camponoius sp.). Rotting, Chemical controls may be needed in some water-damaged wood is used by these ants to nest situations to protect house logs. At present, insec- within, and these logs rarely are utilized for fire- ticidal fumigants are not available for general use wood. Native populations of carpenter ants may on firewood. Consequently, insecticide treatments develop within old rotting wood that has been involve sprays that will kill the insects as they stored improperly for long periods. (See SIA emerge or enter wood. These sprays do not prim- 5.554, Carpenter ants.) arily kill insects already within the wood but can Termites—Unfounded concern is widespread prevent them from moving to healthy plants or with moving termites in firewood or other wood reinfesting the wood. products. Colorado species of termites nest under- Certain commercial formulations of chlorpy- ground and under natural conditions rarely infest rifos (Dursban) are the only materials currently firewood and timber products. Occasional ter- registered for use in control of house log insects. mites found within this wood do not contain However, household formulations are not availa- reproductive stages of the termite. Furthermore, ble. Currently, no insecticides are registered for the low humidity in houses cause the "stragglers" use in control of insects that infest firewood.