196 



NATURAL HISTORY. 



in habits, are the leaf-eaters, mostly brightly colored, hemispherical beetles 

 which feed exclusively upon vegetation, and some of which on this account 

 become of considerable importance. 



Possibly the best known of all the species is the celebrated Colorado 

 potato-beetle, which a short time ago was a subject of such great dread to 

 the fanner. The species was first made known many years ago (1824) by 

 Thomas Say, the naturalist of Long's expedition. He found it upon the 

 upper Missouri, where it fed upon the sand-bur. Gradually civilization 

 spread west, carrying with it the cultivation of the potato. At last this 

 plant reached the territory occupied by the beetle, which at once left its 

 old food and attacked the new. At first its eastward spread was slow, not 

 exceeding on the average fifty miles a year ; but after the Mississippi was 

 passed its rate rapidly increased, so that, in 1874, just fifteen years after it 

 began its travels, it reached the Atlantic coast. It was a noticeable fact 

 that its progress was most rapid on the line of the railroads. It appeared to 



Fig. 183. — Eggs, larva, and adult of the Colorado beetle {JJoryphora decemlineatu) . 



travel on the cars, either climbing upon them or being put inside them 

 with the freight, and thus at times it appeared in localities remote from 

 any other district ravaged by it. In this way it rapidly spread over an 

 area of a million and a half square miles. 



At first its ravages were very considerable, — for there was nothing to 

 check them, — and the farmers feared that the clays of the potato were num- 

 bered. Gradually it was learned that certain arsenical poisons, like Paris 

 green and London purple, could be used against the beetle ; but it is 

 doubtful if this alone would have had any considerable effect in checking 

 the pest. Others, ami far more efficacious agencies, were at work. We 

 have already alluded to the balance in nature, and this stepped in here to 

 avert disaster. The rapid increase in the number of potato-beetles was 

 accompanied by an almost equally rapid development of insect-eating forms. 

 Such an abundance of food allowed individuals to live which otherwise 

 would have perished. Lady-birds ate the eggs and the young, flies feci 

 on them, and bugs sucked their juices, while birds and the despised toads 



