2 INSECT DAMAGE TO MINE PEOPS. 



after they have been transj^iorted from the woods and placed in the 

 mine. The i^rubs of most injurious wood-boring insects can not be- 

 come established in the timber unless the bark is on, because the bark 

 serves as a protective covering under which the eggs can be deposited 

 and affords proper moisture conditions for the development of the 

 young grubs, many of whicli feed on the inner bark before entering 

 the wood. The principal injuries to mine props by wood-boring 

 insects are those caused by roundheaded and flatheaded borers, timber 

 worms, and ambrosia beetles. 



Injury to timbers by roundheaded and flatheaded borers and tim- 

 ber worms consists in burrows in the wood made by grubs, which 

 hatch from eggs laid under the bark by winged beetles. These bur- 

 rows, often of large size, not only decrease the length of service of 

 the timbers, but also their structural strength. Running both trans- 

 versely and longitudinally through the wood, these holes, even if the 

 insects have discontinued their work, afford entrance to moisture and 

 wood -destroying fungi; the decay is thus enabled more rapidly and 

 completely to penetrate the heartwood. 



Injury by ambrosia beetles consists of pinhole and bluing defects 

 in the wood. The pinhole defects also contribute to more rapid 

 decay. 



There is, therefore, a complicated interrelation between these wood- 

 boring insects and wood-destroying fungi in the deterioration of mine 

 timbers. 



INJURY TO PROPS AFTER PLACEMENT IN THE MINE. 



In the Southern States the principal injury to props and other 

 timbers in slope or incline mines is caused by small, white, soft- 

 bodied insects known as " wood lice," white ants, or termites. These 

 destructive insects work in moist or decaying wood. Timbers placed 

 on the heavily timbered slope or incline, extending from 2.50 to 300 

 feet from the exterior into the mine, are attacked by termites, as 

 are those used in " headings " near the surface of the ground. Indi- 

 viduals of the winged form enter the mine and establish colonies at 

 the base of the props. The moist condition of the prop at the base, 

 where the wood is in contact with the ground and where there is 

 usually incipient decay, offers especially favorable conditions for 

 injury by this class of insects. 



The presence of these insects is not easily detected. Their work 

 is hidden beneath an outer shell of wood, often very thin, but always 

 left intact; therefore an ordinary inspection of the exterior of the 

 props will not reveal the presence of the insects or their destructive 

 work. The entire interior may be completely honeycombed while 

 there is nothing on the exterior to indicate the injury. Sometimes 

 an earthy matter — partiall}^ digested wood mixed with earth — is em- 



[Cir. 156] 



