up the Paraguay 41 



hardened to the insect plagues of Guiana and the Orinoco. 

 But they reported that never had they been so tortured 

 as in the Chaco. The sand-flies crawled 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 considerations. The war against 



