The Blister-Beetle and the Oil-Beetle. 



121 



Photo by] [E. Step, F.L.S 



Wasp-nest Beetle. 

 A rare British beetle that might easily be mistaken for a 

 fly. In its grub stage it lives in the nest of the wasp, 

 feeding upon the wasp-grubs 

 actual size. 



It is shown four times the 



then breaks out again through the fourth ring, 

 apparently for the sole purpose of moulting. 

 Although it has not yet east a skin, its appear- 

 ance is utterly altered by the abundant food 

 it has imbibed. The skin is so distended that 

 the black colour, which formerly covered the 

 whole triungulin, now appears only as isolated 

 patches in the middle of each segment. Though 

 the little fellow is now ten times its former size, 

 these black patches remain the same size as 

 they were when it went into its host. The 

 beetle-grub is now one-sixth of an inch long. 

 x'Vt the same time that it emerges through the 

 skin ol its \'ictim it casts its fh'st skin, and 

 becomes a more ordinary-looking grub, but 

 with poorlv developed legs. It attaches itself 

 by the mouth to the under side of the head of 

 the wasp-grub, and lies there " like a collar " 

 until its next moult, " sucking rather than 



eating." When about a quarter of an inch long it moults a second time, and becomes 



much like the grub of a wood-wasp. ^ By the time it is ready for its next change 



it has entirely eaten the wasp-grub, and has become large enough to fill the top of 



the cell of its victim, where it changes 



to a chrysalis. The whole of this life- 

 history from the hatching of the egg 



to this point is comprised in one week. 

 Although this article was sup- 

 posed to be about the blister-beetle 



and the oil-beetle only, we have 



thought it well to include these other 



beetles of similar parasitic habit, as 



parasitism is a very rare phenomenon 



among beetles, and the habit produces 



such similar results in those that 



practise it, though they are not all 



closely related. 



In the vast majoritx' of bc^etles 



the grub is either an active, sIcikUt 



creature with six fairlv long legs, or 



it is somewhat inactive and fat, with 



very short ineffective feet, or none at 



all. It mav be surmised that the 



first-named was the tv])e of the xh 



pr'mitive beetle-lar\-a, and that at a 



later stage in the ex'olution of the race 



.\n Enemy to Locl'sts. 



pieanta-beetle lavs her eggs near the buried cgg-niasses of the 

 Kockv .Mountain locust, and when they hatch the grubs devote them- 

 sehes to feeding upon the locust eggs, and so help to keep down the 

 numbers of a pest whosi; ravages have at times caust'd serious financial 

 difficulties. 



1 Cnvbro. 



