86 FOOD HABITS OF THE GROSBEAKS. 
RELATIONS OF GROSBEAKS AND OTHER BIRDS TO PARASITIC 
’ INSECTS. 
As in the previous pages mention is made of the fact that gros- 
beaks to some extent feed on parasitic insects, and as many other 
birds have the same habit, certain phases of the subject are here 
briefly discussed. Parasites are useful to man because they prey 
upon and reduce the numbers of injurious insects. Hence to the 
extent that birds diminish the number of parasites they are inimical 
to man’s interests. But there is another aspect to the interrelations 
of birds, parasites, and injurious insects. The attacks of parasitic in- 
sects, however numerous they may be, do not result in the immediate 
death of their victims, since time is required for the development of 
the larve within or upon the body of the hosts. Hence the latter, 
after receiving the eggs which ultimately are to prove fatal, some- 
times continue their depredations, and may in a few days ruin 
the season’s crop. Under these circumstances the parasites do no 
immediate good, though they serve to prevent increase of the species 
attacked. It is quite otherwise with birds, which instantly stop 
depredations by killing the insects responsible for them. Often in 
a few days birds extirpate a pest over a limited area, and the crop, 
freed from its enemies, makes successful growth. It is true that at 
the same time all eggs and larve of parasites present in the host 
insects also are destroyed. Though this is regrettable, the effects 
of the loss of the parasites must be regarded as of secondary im- 
portance, since the main purpose—getting rid of the pests—is accom- 
plished. 
Precisely the same result follows the destruction of cocoons, the 
burning of caterpillar nests, fumigation by hydrocyanic gas (which 
is exceedingly destructive to all life), and wholesale killing by contact 
sprays (kerosene, whale-oil soaps, and the like). These methods of 
destroying insects are widely recommended and extensively used, re- 
sulting in the indiscriminate destruction of beneficial and injurious 
insects, foe and friend alike. Moreover, there is no doubt that in 
spite of their indiscriminate effect, these practices result in great good. 
As stated above, birds are chargeable with similar destruction of use- 
ful insects along with the injurious, but it is worthy of note that the 
effects of their feeding have not been judged from the same stand- 
point nor given the benefit of doubt accorded to the work of artificial 
agencies. However, since it has been suggested that birds may so re- 
duce the number of parasitic insects as seriously to restrict their bene- 
ficial services, it may be profitable to inquire into the facts of the case. 
There is no record of an instance in which noticeable injury has been 
caused through the destruction of parasites by birds, and there is 
much evidence going to show that this never happens. First, taking 
