RELATIONS OF BIEDS TO PARASITIC INSECTS. 89 



Comparisons of the usefulness of parasitic insects and of pre- 

 daceous species, both insects and birds, have been made to the dis- 

 paragement of the latter class and in consequence the benefits con- 

 ferred by parasites have sometimes been exaggerated. But in weigh- 

 ing the importance of these statements it should not be forgotten that 

 essentially parasites are dependents. It is farthest from their object 

 to exterminate their hosts, even in a limited area. This result, which 

 in most cases means disaster to the parasite, is, on the other hand, of 

 but little moment to predaceous insects or birds. The latter always 

 have a wide range of prey and even if one food supply is exhausted 

 usually there are others at hand. The best evidence that predaceous 

 foes of insects are worthy of as high consideration as parasitic ones 

 is afforded by the instance of the extermination, successively, by the 

 ladybird, Novius cardinalis, of the cottony cushion scale in Califor- 

 nia, of the fluted scale in South Africa, and of a congeneric scale in- 

 sect in the gardens of Alexandria. Egypt. These are absolutely the 

 most important services in destroying insects ever rendered to man 

 and were accomplished by a predaceous enemy which is chargeable 

 with the same lack of nice discrimination with respect to parasites 

 attributed to birds. 



However, there is no necessity for belittling the services of either 

 of the two great classes of pest destroyers. Both consume a certain 

 proportion of insects directly injurious to man and it is more than 

 likely that either would be hindered rather than helped by the 

 absence of the other. Everything, indeed, points to the conclusion 

 that from the standpoint of man's welfare the loss of either class 

 would irreparably disturb the balance. What has been said by a 

 noted entomologist concerning parasites, namely, that the presence 

 of both parasites and hosts, continuing through thousands of years 

 to the present, implies that an equilibrium is maintained enabling each 

 to live, is just as true of predaceous enemies, both in relation to para- 

 sites and to their common pre}^ There can be no doubt that, even 

 under the greatly changed conditions induced by man, the inter- 

 actions of these classes tend directly toward the establishment and 

 maintenance of a balance. It is probable that this balance can be 

 secured at a lower level in regard to number of individuals only by 

 direct reduction of the injurious species by man, coupled with the 

 best possible protection of both their predatory and parasitic enemies. 



GENERAL CONCLUSION. 



With respect to food habits it appears that the grosbeaks form a 

 group apart from the majority of the finch family, to which they be- 

 long. The members of this group are by no means the extreme vege- 

 tarians they are commonly supposed to be, since on the average they 

 consume about 25 per cent of animal food. The grosbeaks, however, 



