40 THROUGH THE BRAZILIAN WILDERNESS 



through the meshes in the mosquito-nets, and forbade 

 them to sleep; if in their sleep a knee touched the net 

 the mosquitoes fell on it so that it looked as if riddled by 

 birdshot; and the nights were a torment, although they had 

 done well in their work, collecting some two hundred and 

 fifty specimens of birds and mammals. 



Nevertheless for some as yet inscrutable reason the 

 river served as a barrier to certain insects which are men- 

 aces to the cattlemen. With me on the gunboat was an 

 old Western friend, Tex Rickard, of the Panhandle and 

 Alaska and various places in between. He now has a 

 large tract of land and some thirty-five thousand head of 

 cattle in the Chaco, opposite Concepcion, at which city he 

 was to stop. He told me that horses did not do well in 

 the Chaco but that cattle throve, and that while ticks 

 swarmed on the east bank of the great river, they would 

 not live on the west bank. Again and again he had crossed 

 herds of cattle which were covered with the loathsome 

 bloodsuckers; and in a couple of months every tick would 

 be dead. The worst animal foes of man, indeed the only 

 dangerous foes, are insects; and this is especially true in 

 the tropics. Fortunately, exactly as certain differences 

 too minute for us as yet to explain render some insects 

 deadly to man or domestic animals, while closely allied 

 forms are harmless, so, for other reasons, which also we 

 are not as yet able to fathom, these insects are for the 

 most part strictly limited by geographical and other con- 

 siderations. The war against what Sir Harry Johnston calls 

 the really material devil, the devil of evil wild nature in the 

 tropics, has been waged with marked success only during 

 the last two decades. The men, in the United States, in 



