57 



species of Mites that are what I have called "Cannibals," haunting 

 leaf-galls constructed by certain Plant-lice and Bark-lice, and feed- 

 ing apparently upon the tender bodies of the unfortunate young lice. 

 Galls made by other groups of insects they do not usually enter, be- 

 cause these last are invariably closed, till the gall-maker gnaws his 

 way out. But galls made by Plant-lice and Bark-lice — which insects 

 have no jaws at all to gnaw with, but only a beak to suck with — always 

 burst open towards the latter part of their existence, so as to allow the 

 young Lice a free exit into the extemai world. Hence into these the 

 wandering Cannibal Mites, Avho are always remarkably fleet-footed in 

 the mature state, find a ready entrance, and often carry death and 

 desolation into what was before the happy home of a flourishing 

 colony of Lice. "Eat and be eaten; kill and be killed."' Everywhere 

 this is the great imiversal Law of Kature. 



Of these Cannibal Mites, I have discovered that there is at least 

 one species, and perhaps more than one, that preys most extensively 

 upon the eggs of the Oyster-shell Bark-louse; insomuch that upon a 

 particular apple-twig infested by these Bark-lice I have found, on 

 lifting and carefully examining six hundred scales about the last of 

 October, that at least two-thirds of the whole number were either 

 already gutted, or were undergoing the process of being gutted, by 

 the minute larvse of a Mite.* What I believe, though I am not 

 absolutely certain, to be the eggs of this Mite are deposited here and 

 there upon the bark among the scales, in little patches of six or eight, 

 and are exceedingly minute, smooth, shining, perfectly globular 

 bodies, rather less in diameter than the transverse diameter of the 

 egg of the oyster-shell Bark-louse. Most of them are blood-red, but 

 some, which appear to be the empty shells of such as have already 

 hatched out, are transparent and colorless. Eepeatedly, on raising the 

 Bark-louse scales both in the autumn and in the early spring months, 

 I have found from one to eight of the larva of some kind of Mite — 

 whether hatched out or not from the above-mentioned eggs is not per- 

 fectly clear — interspersed among the eggs of the Bark-louse. la 



*Duriiig my attendance at tlie inauguration of thn Horticultural Society 

 of Northern Illinois, at Mt. Carroll, December 18th— 20tli, 18G7, and before I 

 had said a word there about these Cannibal Mites^ but after the whole of 

 this chapter was in the hands of the printer, I was much gratified by hearing 

 Dr. H. Shinier, of Mt. Carroll, inform the meeting that he had himself dis- 

 covered that the imported Bark-louse was preyed on quite extensively by a 

 species of Mite {Acarus.) Thus, as often happens, the same discovery has 

 been made at the same time^ by two independent observers. Of course^ Dr. 

 Shimer's evidence is cumulative proof, if any he needed by any one, of the 

 reality of the discovery. — December 2L 1867. 



