TWO INSECTS OF THE ORCHARD — SNODGRASS. 



493 



the cases, exposing themselves only during the brief journey from 

 the mine to winter quarters, but a small percentage of the autumn 

 brood of caterpillars escapes destruction at the mouths of enemies. 

 Most of the cases examined in the spring are found to contain not the 

 original occupant, but cither the grub or the pupa of another insect, 

 a usurper, a parasite that by some means gained entrance to the house, 

 destroyed the rightful owner, and without any skill or work of its 

 own, enjoys the protection that the shield-bearer worked so hard to 

 insure for itself during the period of its helplessness. It was not by 

 any negligence on the part of the shield-bearer caterpillar that the 

 parasitic grub invaded its home, nor was it through any cleverness 

 of the changeling. It was the mother of the intruder that got it into 

 its present comfortable quarters, for the grubs are the young of a 



Fig. 4. — A parasite of the Resplendent Shield-Bearer (Cirrospilus fiavicinctun Riley). 

 A, Winter case of the shield-bearer with one side removed, showing the parasitic grub 

 (a) and the remains shield-bearer caterpillar (b) ; B, remains of a parasitized cater- 

 pillar reduced to a dry flake ; C, the pupa of the parasite, side view ; D, the same, 

 back view ; E, the adult parasite. 



minute, wasplike insect which, with a needlelike ovipositor, is able 

 to pierce the mine and insert an egg probably into the body of the 

 caterpillar itself. 



The history of this particular parasite of the shield-bearer is per- 

 haps not known, but, with others related to it, the egg hatches 

 within the bod} 7 of the caterpillar, where the young grub feeds on 

 the caterpillar's blood, but does not destroy its life till the caterpillar 

 has spun its cocoon. Then when the grub is full grown it comes out 

 of the body of its long-suffering host, leaving the latter weak and 

 emaciated, to die of exhaustion, while it changes to a pupa and 

 finally to the adult of its own species. The writer has seen this shield- 

 bearer parasite, or another very similar to it, piercing the mines of the 

 trumpet-miner of the apple. The dead shield-bearer caterpillar 

 found in the parasitized cases by spring is usually reduced either to 



