88 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



sistence. Flies appear to be subject to parasitism only to a compara- 

 tively slight extent but some of them are decimated by fungal diseases. 



Discussion. — While flies in the adult stage appear to have a degree 

 of freedom from predators, it is evident that the immature stages of 

 many groups of them pay a heavy toll ; the chief food of predacious 

 fly and beetle larvae that live under bark, in decaying fungi or carrion 

 are the fly larvae they find there ; the chief food especially of the 

 young of a great many fresh-water fishes again are fly larvae and 

 pupae ; and a very important element of the food of the mold- and 

 earth-traversing shrews and moles are the larvae of flies. Fly larvae 

 perish in large numbers also because of the drying up or exhaustion 

 of their breeding nidus. Possibly some relative good fortune for the 

 adults may be only compensatory, but so little is known about the 

 subject that discussion is not on a very firm basis. Regarding the fate 

 of adults it is worth while recalling the all but universal destruction at 

 times wrought among the ranks of its hosts by the fungus Empitsa 

 muscae. 



Evidence showing the importance of availability as regulating the 

 consumption of dipterous food is presented in testimony of an Alaskan 

 correspondent about birds feeding on mosquitos. These insects, so 

 much more prominent an element of the insect fauna of that territory 

 than they are in the United States, apparently are fed upon much 

 more freely by birds. This correspondent, A. H. Twitchell, a reindeer 

 breeder, reports all small'birds frequenting the vicinity of his camp, 

 as myrtle, blackpoll, and Wilson's warblers, Gambel's sparrow, and 

 Alice's thrushes preying regularly on mosquitos and feeding them 

 extensively to their young. 



HYMENOPTERA (ANTS, BEES, WASPS ) 



Protective adaptations. — In selectionist writings, Hymenoptera 

 usually are classed as the very acme of protected insects, and pro- 

 tective qualifications are broadly assigned to the whole group. Poulton 

 says : "Ants and wasps are known to be aggressive dominant insects 

 avoided by the majority of insect-eating animals." (Essays on evolu- 

 tion, p. 281, 1908.) Drummond, in similar vein, declares that " well- 

 armed or stinging insects are always conspicuously ornamented with 

 warning colours. The expense of eating a wasp, for instance, is too 

 great to lead to a second investment in the same insect, and wasps 

 therefore have been rendered as showy as possible so that they may 

 be at once seen and as carefully avoided. The same law applies to 

 bees, dragonflies, and other gaudy forms ; and it may be taken as a 

 rule that all gaily-coloured insects belong to one or other of these two 



