THE BEWITCHED COCOONS Jl 



at your window. For your 'wasps' were not true wasps but 

 ichneumon flies ; the large one is called Ophion macrurum, and 

 the swarm which you imagined might be the ' young ones ' of 

 the ' big wasp ' are another species, from the third cocoon, with 

 the same evil parasitical ways. Briefly told, their doings are as 

 follows : These two species know a Polyphemus caterpillar when 

 they see him, and to find them feeding among the leaves is the 

 end and aim of their existence. Once discovered, they alight 

 upon him, either thrust their stings into his body, or simply 

 penetrate the skin, and, much against his will, lay a number of 

 eggs, for the so-called 'sting' of the ichneumon flies is more 

 properly the ovipositor, through which the eggs are conducted 

 into the bodies of their victims. The caterpillars of the Cecropia 

 and Prometheus moths are frequently to be found with their 

 backs speckled with the tiny white eggs nearly the size of the 

 letter i of this page. We shall get no moths from these cater- 

 pillars. The ichneumon fly has sealed their doom. These eggs 

 hatch into minute larvae that penetrate the caterpillar's body, 

 and feed upon the fatty portions, avoiding any attack on its 

 vitals, and thus permit it to attain its full growth, and even to 

 spin its cocoon as you have seen. 



When once thus securely provided with a warm house for the 

 winter, the ichneumon grubs, now nearly full grown, proceed to 

 devour what remains of the unfortunate caterpillar host, until 

 occasionally no vestige of him remains. With this final repast 

 the larvae reach their full size, and then proceed each to spin a 

 cocoon for itself, thus filling the cavity of the Polyphemus cocoon 

 with their own silky cases, packed side to side so solidly as to 

 take the hexagonal shape of a honey -comb. The grubs then 

 change to pupse, and eventually make their exit through small 

 holes in the outer cocoon, and fly abroad, to the terror of future 

 Polyphemus caterpillars and little girls. 



" But that larger fly is certainly a formidable affair, and you are 

 hardly to be blamed for a reasonable amount of caution ; for 

 though its sting is not so formidable an instrument as the smaller 

 insect possesses, it is capable of inflicting a severe wound, as I 

 know from experience. 



" So here you have the mystery solved an instance of a phase 



