THE ORTHOPTERA OF MINNESOTA. 



29 



in the infested region does not always admit of using more 

 than one hopper-dozer at a time. But wherever it is level 

 and free of stones as many as four hopper-dozers can be 

 joined together by means of short ropes, thus forming a con- 

 tinuous pan some forty feet long. Immense numbers of insects 



Fig. 8.— Large hopper-dozer, with partitions. After Riley. 



can thus be captured and killed. Formerly a mixture of coal 

 tar with oil, or coal tar alone, was used; this has one 

 advantage, but only an imaginary one, i. e., the farmers 

 operating the dozer actually see the enemy perish before 

 their eyes, while, when using nothing but kerosene oil, only 



Fig. 9. — Smaller hopper-dozer. After Riley. 



one out of about every ten locusts is seen dying in the pan, nine 

 jumping out again. But as these almost invariably perish 

 later it matters but little. As the young and tender locusts 

 are killed whenever they come in contact with such a pene- 



