USEFUL INSECTS EATEN BY THE BLACKHEAD. 



69 



members of this order are the parasitic Hymenoptera, which lay 

 their eggs in the eggs or young of other insects. Remains of insects 

 of this class from the stomach of one grosbeak were identified and 

 they amounted to 22 percent of its contents. Two bees were found 

 in another stomach, one of which was a worker honeybee. These 

 are the only beneficial species of Hymenoptera from stomachs of 

 this grosbeak positively identified, but it is probable that many of 

 the unidentified forms belong in the same category. In all, 58 gros- 

 beaks fed upon wasps, bees, and ants, very many of which selected 

 large wasps, which were most probably workers of some social 

 species the loss of which would not 

 be noticed. Eleven blackheads ate 

 ants, including both pupse and 

 adults, for which the birds are to 

 be commended, as many ants are 

 prejudicial to the interests of man. 



Summing up the relations of the 

 black-headed grosbeak to beneficial 

 insects, Hymenoptera constitute 2.56 

 percent of the food, not all of 

 which, as just noted, is to be set 

 down against the bird. The wholly 

 useful fireflies amount to 2.38 per- 

 cent, the mainly beneficial ground 

 beetles to about 1 percent, while the 

 ladybirds are a mere trace. Thus 

 only about 5 percent, or a little 

 more, of the bird's food consists of 

 insects the destruction of which is 

 prejudicial to the welfare of man. 

 Even were the bird not useful other- 

 wise, this showing would hardly jus- 

 tify reprisals. 



As a matter of fact, however, the 

 blackhead is far from useless, since the remainder of the animal food, 

 which is fully 11 times the bulk of the useful insects, consists of pests 

 upon some of which no other bird is known to prey so extensively. 

 Beetles of various families constitute about half the bulk of these 

 harmful insects, and 28.71 percent of the total food. A much greater 

 number of grosbeaks preyed upon leaf beetles (Chrysomelida?) than 

 any other family, these composing 17.98 per cent of the diet. One 

 hundred and seventy-two blackheads, or almost four-fifths of the 

 total number examined, captured leaf beetles, which are said to in- 

 clude among their ranks more enemies of crops, shade trees, and 

 ornamental plants than any other family of beetles. 



Pig. 33. — An Australian ladybird 

 (Rhizobius ventralis). (From Mar- 

 latt, Bureau of Entomology.) 



