232 



THE AMERICAN ENTOMOLOGIST. 



all the months mentioned taken together 

 (except September), I invite especial atten- 

 tion. Being derived from a much larger 

 nvmiber of specimens than any of the 

 monthly averages, they are much less likely 

 to be affected by accident or error. They 

 give, furthermore, the basis for an estimate 

 of the total effect of the bird, year after 

 year ; and from this we should be able to 

 predict the probable effect of a destruc- 

 tion or diminution of the species. 



Taking up first the injurious insects de- 

 stroyed, we find that these include 24 per 

 cent, of Lepidoptera, nearly two-thirds of 

 which were recognized as Noctuida, 3 per 

 cent, of leaf-chafers, i per cent, of curcu- 

 lios and 1 2 per cent, of Orthoptera, — chiefly 

 grasshoppers, — a total of 40 per cent, on 

 this side of the account. On the other 

 hand the ichneumons amount to 4 per 

 cent., the Carabida: to 9 per cent., soldier 

 beetles to 2 per cent., soldier bugs to 3 per 

 cent., and spiders to 9 per cent. — a total of 

 27 per cent, of predaceous and parasitic 

 forms. Other elements are, ants 4 per cent., 

 Diptera only a trace, Aphodii 7 per cent., 

 TcnebrioiiidcB i per cent., lulidm 2 per 

 cent, and vegetable food 15 per cent. 

 The edible fruits amount to about only 

 I per cent, of the food of these 86 speci- 

 mens. 



Comparing with the Turdidce, we find 

 that the Bluebird is essentially a thrush in 

 food. From the robin it differs principally 

 in the larger number of Hymenoptera (8 to 

 i), and Lepidoptera (24 to 18), the lack of 

 Diptera (robin 18 per cent.), the excess of 

 Aphodii (7 to 2), oi Cydttidcs {rohm only a 

 trace), of Orthoptera ( 1 2 to 5), and of spiders 

 (9 to a fraction); but especially in the mat- 

 ter of edible fruits (i to 28). These differ- 

 ences are but little greater, however, than 

 those among the thrushes themselves. 

 Compared with the thrush family as a 

 whole, its salient peculiarities are its 

 neglect of Diptera and garden fruits, and 

 its preference for cutworms, grasshoppers, 

 CydnidcB and spiders. 



What now shall we say of the economi- 

 cal relations of this bird ? According to 

 the estimate of Mr. Walsh, previously cited. 



the Bluebird does at least twenty times as 

 much harm as good, — that is to say, the 

 beneficial insects destroyed would them- 

 selves have made away with twenty times 

 as many injurious insects as the birds them- 

 selves have eaten. Admitting that Mr. 

 Walsh's estimate was exaggerated, it surely 

 was not twenty times too large; and, even 

 if it were, we could merely look upon the 

 Bluebird as harmless, indeed, but as useless 

 also. 



And yet, in the face of this, I venture to 

 doubt that a case has yet been made out. 



In the first place, nothing has been 

 learned of the food of the young ; and 

 there is some reason for supposing that 

 birds select for their young the softer kinds 

 of insects. This supposition, founded 

 chiefly upon the statements of M. Florent- 

 Prevost, of Paris, is contradicted, it is true, 

 by observations of the food of the young 

 mocking-bird;* and whatever deficiency 

 of credit may be due to this neglect of the 

 food of the young is compensated in part, 

 at least, by the fact that the number of 

 caterpillars eaten is doubtless over-esti- 

 mated, in comparison with hard insects, as 

 their flexible skins remain in the stomachs 

 of birds longer than the hard structures of 

 insects. This is exactly contrary to the 

 usual supposition; but the frequent occur- 

 rence of numbers of the emptied and 

 twisted skins of cutworms in the stomach, 

 still recognizable as Noctuidce, when not 

 even a fragment of a single head remains, 

 is sufficient evidence that the hard parts 

 break up and disappear before these deli- 

 cate but yielding skins. 



Secondly, while our knowledge of the food 

 of Arctians, cutworms and grasshoppers ; 

 is sufficiently definite and full to enable us ' 

 to predict with certainty exactly what would 

 happen if those eaten by bluebirds were 

 allowed to live and multiply, we have not 

 the same complete and certain knowledge 

 of the food and habits of the different 

 genera of IchneumonidcB, the ground 

 beetles, the soldier bugs and soldier 

 beetles. 



One hundred bluebirds, at thirty insects 



* Trans. 111. State Hortic. Soc, Vol. xiii.. p. 1S8, footnote. 



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