CARNIVOROUS INSECTS 187 



when it comes in at open windows — hence the old saying 

 that "flies begin to bite before rain." 



Chief among the flies whose females alone are san- 

 guinivorous are the gnats and mosquitoes (Culicidcv), and 

 the horse- or gad-flies and their allies (Tabanidce). The 

 grey, green-eyed "cleg," or rain breeze-fly (Hccmatopota 

 pluvialis), is probably the commonest British representa- 

 tive of the latter family. During the summer months it 

 is a provoking attendant upon man and beast, especially 

 in woodland districts. The great ox gad-fly (Tabanus 

 bovinus) — a robust and handsome insect with a wing- 

 expanse of almost two inches — generally attacks horses, 

 cattle, and deer, which it punishes severely. Of the 

 " stinging " proclivities of mosquitoes and their lesser 

 relatives the midges (Chironomidcc) there is no need to 

 write, as everyone has experienced the attentions of these 

 winged nuisances. We have already seen that poisonous 

 secretions are mingled with the saliva of many insects ; 

 and this fact accounts for the persistent pain and inflam- 

 mation which frequently follow a bite. But there is a far 

 more serious aspect of the case, namely, that many insects 

 are known to infect the blood of men and animals with 

 the active elements of disease. We shall recur to this 

 matter when we discuss insects from a purely anthropo- 

 logical standpoint. 



Some insects are permanently parasitic, being com- 

 pletely dependent in all their stages upon some other 

 creature. Such are the Mallophaga and the Anoplura 

 (pages 67 and 74) ; also the spider-flies (Hippoboscidce) 

 and their allies. Certain of the latter are winged, others 

 wingless ; but the winged species seem only to make use 

 of their power of flight in order to get from one host 

 to another. The forest-fly (Hippobosca equina) is especi- 

 ally abundant in the New Forest, where it may sometimes 



