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 menaces 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
