io6 INJURIOUS AND USEFUL INSECTS 



This formidable weapon consists of an outer pair of valves, 

 and within them of a guide and a pair of darts, which can be 

 separated into three, or combined into one. Here we have 

 evidently the same parts as in the borer of Sirex (p. loo); in 

 the bee also (p. 88) we make out with no great difficulty the 

 same valves,* guide and darts. Even the saws of a saw-fly, 

 though very different at first sight, can be referred to the same 

 common plan; all are homologous, or answerable organs. 

 The darts of Pimpla are roughened by teeth, which enlarge the 

 hole, and diminish the risk of the borer becoming jammed, an 

 accident which happens now and then to wood-borers. Thus 

 furnished, the female Pimpla sets out to discover a wood- 

 eating longicorn larva, or the larva of a solitary wasp. By what 

 exercise of her long, vibrating antenna she discovers the larva 

 deep in the solid wood we cannot tell, except that the antennse 

 (feelers) are brought as close to the spot as possible, and 

 passed down into the hole wherever that is discoverable. 

 Then she raises her abdomen into the air, pointing the 

 separated valves almost vertically upwards, and passes the 

 inner tube of the borer into the wood. To judge from the 

 movements of the abdomen, the darts, in drilling a hole 

 through solid wood, are worked in and out, up and down, and 

 also screw-wise, being steadied all the time by the hind legs. 

 At last, with a throb of the abdomen, an egg is sent down the 

 long tube, and the task of the Pimpla-fly is accomplished. It 

 seems to be left to the larva which issues from the egg to 

 make the actual attack upon the owner of the gallery. Another 

 Pimpla reaches the grub of the goat-moth in its tree ; a third 

 attacks the Sirex-larva. There are also Pimplas with short 

 borers, which lay their eggs upon the external feeding larvae 

 or the pupae of Lepidoptera. 



Rdaumur, in one of his graphic chapters on the history of 

 insects, t tells us how he saw in August a small four- winged 

 fly settle upon a caterpillar of the cabbage white. The fly 

 chose her point of attack, pushed out a slender borer, nearly 

 as long as her body, and buried it almost to its base in the 

 caterpillar. The victim bore the wound patiently, making 

 only slight movements, to which the fly paid no attention. 

 The borer was withdrawn, and inserted again and again, 

 always at the junction of two of the hinder segments. Sus- 

 * Called sting-palps in the bee. t Vol. II. Mem. xi. (1736). 



