Insects Can Take Their Toll
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Wood Magazine

Insects Can Take Their Toll

Water, fungi, oxidation, enzyme stain, and decay all cause wood to deteriorate.

Insects Can Take Their Toll
Insects Can Take Their Toll

Insects Can Take Their Toll

Then there are insects, plenty of them. Insects recycle dead, down, and wounded trees into fertile soil and plant nutrients. Unfortunately, these little recyclers don't observe "off limit" signs. They'll eat wood destined for your shop (or the wood already there) as well as what loggers leave behind. Here's a roundup of those that make their mark.

Some insects focus only on living trees and green logs Insect species in this category actually number in the thousands. But woodworkers usually never see these culprits, only the results of their activity.


Insects Can Take Their Toll

Fly larvae create distinctive marks The dark, thin streaks of varying length running with the grain that you'll often spot on basswood, birch, cherry, maple, and willow boards were made by fly larvae. These pith flecks result from the burrowing of the larvae down through the cambium layer of the living tree toward the ground. The wound heals after the larvae pass, but the tissue turns dark. The pith flecks don't weaken the wood. It only looks bad.


Insects Can Take Their Toll

Bark beetles engrave as they go Many insects attack the inner bark of trees (mostly conifers) and freshly cut logs. As they excavate around the trunk, they leave a telltale trail. Visible entrance holes with expelled frass (fecal matter, bark, and wood powder) indicate their work. Because these beetles live on fresh logs and living trees, they perish with the later processing of the wood.

Horntails and others do boring work Some insects bore into trees, logs, and freshly sawn lumber to simply feast. The most common are the pine sawyers and the horntails. The 1/4" to 1" grub holes they leave behind indicate their past presence. You'll find their tracks in hardwoods and softwoods, and in sapwood as well as heartwood. Kiln drying kills their larvae. But if their activity was extensive, the lumber is weakened and its appearance downgraded.


 

Termites and Carpenter Ants
Insects Can Take Their Toll

Termites and Carpenter Ants

These tough guys like wood and damp feet While common termites and carpenter ants--both social enough to live in colonies--can and will tear through your woodworking stock, it's unlikely. That's because they both prefer moisture. So unless you store wood where it's damp, or where termites can tunnel their way to it from moist ground, you're not likely to encounter these critters.


Insects Can Take Their Toll

Other bugs eat seasoned and even kiln-dried wood Beetles in this category prove numerous as well as aggressive. They're Enemy Number One for woodworkers.

Ambrosia beetles damage hardwoods and softwoods The pin holes up to 1/8" in diameter often seen in oak and other woods are signs left by the ambrosia beetle or other anobiid beetles. No tree species is immune to them because they primarily attack the sapwood of green wood and that being air-dried. Once the wood dries there's no threat. The holes they've mined usually don't weaken the wood, yet a fungus they carry severely stains it. The holes and the frass coming from them give away their presence.


Insects Can Take Their Toll

Powder-post beetles like hardwood sapwood best With a strong preference for hardwoods, powder-post beetles go after the sapwood of seasoned and even kiln-dried lumber. Because the adults deposit their eggs in the wood pores, only species that have sufficiently large pores get their attention. In the United States, you'll find powder-post beetle damage in ash, hickory, and oak, although other species are susceptible, too, including black walnut. When adults emerge from the wood, usually in spring and summer, they leave 1/32"-to 1/18"-diameter holes. Fine, powdery frass near the holes marks their ongoing action, which can eventually render stock useless.


 

Critter-containment tactics
Insects Can Take Their Toll

Critter-containment tactics

The necessary measures to kill insects and control or contain insect infestation in wood vary with the type of insect.

For insects that only chew green wood, take away moisture With insects that love green wood, the best protection is getting the wood dry as quickly as possible without degrading it. Always stack wood for air-drying with stickers of dry, uninfested wood. The stickers allow air to circulate between the boards and more quickly dry the exposed surfaces. It's also a good idea to remove all bark (wane) from board edges before seasoning or storing. And kiln-drying over 130 normally kills most insects that like their wood moist.

Insects living off dry hardwoods require special measures Although the primary culprit in this category is the powder-post beetle, there are others. Prevention and eradication methods remain the same, however.

Because powder-post beetles invade only hardwood sapwood, buy boards with the smallest amount (or rip it off) if you plan to store the wood for any length of time in a place where the bugs may enter. That could be a shed or other building subject to the elements.

Pretreating wood surfaces with a borate compound--boron and oxygen--protects against beetle infestation. Mixed in a 10-percent solution with water, the borate should be sprayed or brushed directly on and into the holes of unfinished wood. In infested wood, the larvae and adult beetles die after digesting the treated boards. (You'll find one product--Termite Prufe--at major hardware stores or call 805/565-1566.)

Other post-infestation treatments include fumigation, heating, and freezing (-40 degrees F for days). But for the majority of home woodworkers, they're all relatively impractical.


 

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Wood Magazine