THE OAK PBUNEE. 



are able to survive the immersion to which they are sometimes sub- 

 jected for many days together during thaws and rainy spells in winter. 



Another explanation of the limb's amputation occurs to the writer. 

 Those who have reared beetles from hard wood can not have failed to 

 observe that the larva before transforming cuts through the wood 

 until it reaches the bark, which is left untouched and serves to protect 

 the insect from marauding birds or other enemies. "When the beetle 

 develops it has only to gnaw its way through this thin layer of bark to 

 eifect its exit. There are undoubtedly some wood borers which are 

 provided in the beetle state with mandibles sufficiently powerful to 

 enable them to penetrate hard wood (Mo;iohammus, for example), but 

 the majority, among them Elaphidion, are not thus favored, and 

 would be utterly unable with their weaker boring organs to escape, 

 and would perish in their burrows had they not while larvas exca- 

 vated the necessary channel for their exit. These exit channels 

 usually run at an angle to the axis of the wood. Now, in the case of 

 our Elaphidion, which usually Uves in a slender hmb which it bores- 

 longitudinally, there is no room to place a branching, transverse 

 channel; accordingly the larva severs the twig and when it becomes 

 a beetle it cuts its way through the plug of castings. 



As to Fitch's claim that the larva varies its operations to suit the 

 different sizes of limbs, the average infested twig is of about the 

 thickness of one's finger, and it is probable that the larva conunences 

 proceedings late in the season with the approach of cold weather 

 when it is about full grown and ready for hibernation. To cut off 

 the limb is a labor of some magnitude for so smaU a creature and may 

 require several days for completion. It has a limited amount of 

 energy, being now toward the end of its active existence as a borer, 

 and the cooler weather serves to repress this energy, which is sufficient 

 for cutting away all the wood in a small twig, but is inadequate for a 

 larger one. The wood of a large branch is harder, and the insect 

 ceases work, perhaps from exhaustion or from cold, or because its 

 instinct impels it to cut a certain amount, and when that is accom- 

 plished to cease, its work being ended. At the close of his narra- 

 tive Fitch says, in spite of a previous assertion that the insect never 

 miscalculates, that — 



in at least three-fourths of the fallen limbs no -worm is to be found; and an exam- 

 ination of them shows that the insect perished at the time the limb was severed 

 and before it had excavated any burrow upward in its center, no perforation being 

 present except that leading into the lateral twig. It is probable that in many instances 

 the limb broke when the insect was in the act of gnawing it asunder, either from its 

 own weight or from a wind arising whilst the work was in progress. 

 (Clr. 130] 



