12 



will do the most good and the least harm, while the check 

 kept by the crow on the increase of the robin may prevent the 

 latter from destroying too many ground beetles. If certain low- 

 feeding caterpillars should become so numerous as to be injuri- 

 ous, ground beetles and robins would feed largely on them. The 

 caterpillars would then largely take the place of the beetles in 

 the robin's diet. The beetles therefore would increase in num- 

 bers, and the force of both bird and beetle would be exerted to 

 reduce the caterpillars to harmlessness. This accomplished, the 

 robins would again attack the ground beetles, and thus tend to 

 reduce them to normal numbers. 



Let us now go back to the beginning of our chain of de- 

 struction. Eagles, hawks, owls and raccoons may indirectly 

 swell the numbers of the robins by limiting the increase of the 

 crow. But hawks and owls also prey on the robin, and by 

 dividing their predatory activities between robin and crow assist 

 in keeping both birds to their normal numbers. Whenever 

 crows become rare, robins as a consequence would become very 

 numerous, were it not that hawks also eat robins. (Hawks and 

 owls also eat some species of insects that are eaten by both 

 robin and crow.) 



There are compensations in the apparently detrimental career 

 of the crow. An omnivorous bird, it takes any food that is 



Cutworm moth and its caterpillar, eaten by robins, crows and 

 other birds. 



plentiful and easily obtained. It is a great feeder oit May 

 beetles (miscalled "June bugs"), the larvae of which, known as 

 white grubs, burrow in the ground and sometimes devastate 

 grasslands, and also injure the roots of many other plants, in- 

 cluding trees. 



The crow is also a destroyer of cutworms, which are the 

 young or larvae of noctuid moths or "millers" such as are 

 commonly seen fluttering from the grass by any one who dis- 

 turbs them when walking in the fields. Robins also feed 



