UTILITY OF BIRDS IN NATURE. 9 



The general fitness of the Crow is admitted by all. Un- 

 doubtedh' it has a useful work to perform in the world ; but 

 a careful study of its food habits shows so many apparently 

 harmful traits that it may well leave the investigator in some 

 doubt as to the Crow's value in the general plan. Crows 

 rob the nests of Robins, eating very many eggs and young 

 birds ; they therefore constitute a serious check on the in- 

 crease of this species. Robins feed largely on common black 

 beetles, called ground beetles (Carabidtij), which run about 

 on the ground, hiding under stones and other rul)bish. As 

 these beetles are not quick to fly by day, 

 and are easily caught, they form a consid- 

 erable part of the food of many ground- 

 frequenting birds. But ground l)eetles 

 feed, to a greater or less extent, on other 

 insects. The cpiestion then arises. Is not 

 the Robin doing harm in killing ground 

 beetles, and does it not merit the destruc- 

 tion of its eggs and young by the Crow? pig. 2.-(;n.uiui 

 If the Robin's habit of eating these beetles huetw. 



is harmful, is not the Crow rendering a service by destroy- 

 ing a bird so apparently destructive as the Robin ? Perhaps, 

 if there were too many Robins, they might eat too many 

 ground beetles, and thus l)ecome the indirect cause of the 

 destruction of much vegetation, by saving the lives of the 

 caterpillars and other harmful insects that the ground beetles, 

 had they been left to themselves, might have destroyed.^ 



Many ground beetles that are eaten by the Robin feed 

 much on vegetal)le matter.^ This makes these beetles doubly 

 useful in one respect, for they can maintain their numbers 



^ These questions can be answered only by one having a thorougli knowledge 

 of the food of our ground beetles, — a knowledge which no living man yet pos- 

 sesses ; but enough has been learned to throw some light on their food habits. 

 Insects that feed promiscuously on other insects are generally classed as bene- 

 ficial in so far as tbey take insect food, even though they may destroy some 

 so-called useful insects; for, as the so-called injurious insects far outnumber the 

 useful ones, it is considered safe to regard the habit of feeding on insects a bene- 

 ticial one. 



^ The ground beetles of the genus Calosoma and those of some closely allied 

 genera are believed to feed entirely on animal food, as their structure fits them 

 for that alone. They feed ravenously upon both beneficial and injurious insects, 

 and when too numerous they devour one another. These are not tlie beetles that 

 are generally eaten by tlie Robin, however, but rather by the Crow. 



