DEFECTS IN TIMBER CAUSED BY INSECTS 



39 



DEFECTS CLASSED AS BLACK CHECK 



" Black check " is the lumberman's name for a common defect 

 consisting of a dark stain in the heartwpod and sapwood, surrounded 

 by thickened, curled, or abnormal layers of wood (fig. 41) (6). It 

 should not be confused with stains associated in the wood with other 

 boring insects (as ambrosia beetles), where the wood is rarely dis- 

 torted. Although also caused by other agents, it particularly applies 

 to the defect in western softwoods (hemlock, fir, spruce, and yellow 

 pine) produced by the maggots of several small flies 38 or moths, 39 

 but the term is also used for a somewhat similar defect in oaks 

 produced by the larvae of large beetles. 40 (Figs. 42 and 43.) 



Fig. 42. — Pile of logs with grub holes made by round-headed borer (Romaleum 

 rufulum). This defect is considered as " wormholes, no living -worms or decay" 



These defects are caused by the insects injuring the growing tissue 

 of the tree and killing a small area of the outer layers of wood. 

 The subsequent growth of the tree finally heals over this injury, but 

 many annual la3 T ers are stained and distorted. The original small 

 pocket or cavity where the insect was working remains, and in conif- 

 erous trees it fills up with pitch. 



Western hemlock contains more of this injury than any other soft- 

 wood. In quarter-sawn (vertical-grain) wood the checks appear as 

 small seams one-half to 1 inch long, with one side curly, while in 

 bastard-sawn (flat-grain) boards they appear as oval or rounded 

 spots from one-half to 1 inch in diameter. The defects in other 

 conifers are similar but not so numerous. 



38 CheiJosia spp. 



33 Tarharmonia. 



40 Romaleum sp. and Goes sp. 



