OAK-BARK CATERPILLAR. 197 



into the solid wood, to the depth sometimes of three 

 inches, and seldom if ever less than two, forming 

 holes, nearly semi-cylindrical, and of exactly the form 

 of the grub which inhabits them. At first sight one 

 would wonder how so small and seemingly so weak 

 an animal could have strength to excavate so deep a 

 mine ; but when we examine its jaws our wonder 

 ceases. These are large, thick, and solid sections of a 

 cone divided longitudinally, which, in the act of 

 chewing, apply to each other the whole of their inte- 

 rior plane surface, so that they grind the insect's 

 food like a pair of millstones. Some of the grubs 

 ate hatched in October ; and it is supposed that about 

 the beginning of March they assume their chrysalis 

 state. At the place in the bark, opposite to the hole 

 from whence they descended into the wood, the per- 

 fect insects gnaw their way out, which generally takes 

 place betwixt the middle of May and the middle of 

 June. These insects are supposed (o fly only in 

 the night, but during the day they may generally be 

 found resting on the wood from which they were 

 disclosed. The grubs are destitute of feet, pale, folded, 

 somewhat hairy, convex above, and divided into thir- 

 teen segments. Their head is large and convex *. 



It would not be easy to find a more striking ex- 

 ample of ingenuity than occurs in a small caterpillar 

 which may be found in May, on the oak, and is sup- 

 posed, byKirbyand Spence, to be that of the PyraUa 

 etrigulalis. It is of a whitish yellow colour, tinged 

 with a shade of carnation, and studded with tufts of 

 red hairs, on each segment, and two brown spots 

 behind the head. It has fourteen feet, and the upper 

 part of its body is much flatter than is common in 

 caterpillars. When this ingenious little insect begins 

 to form its cell, it selects a smooth young branch 



• Kirby in Linn. Trans, vol. v. p. 246, and Introd. ii. 



