INSECT FOOD OF THE BLUE GROSBEAK. 81 
weeds, a work of which the blue grosbeak assumes a proper share 
and the value of which in the aggregate is immense. 
Before leaving the subject of vegetable food, it should be mentioned 
that one blue grosbeak, collected in the District of Columbia, had fed 
largely upon the seeds of wild rice (Zizania aquatica). This plant 
is an important source of food for many larger birds, especially ducks 
and geese, but is not generally sought by the smaller species. 
ANIMAL Foop. 
The blue grosbeak consumes more than twice as much animal as 
vegetable food, and it consists of snails, spiders, and various insects. 
The latter constitute 65.7 out of 67.6 percent, the entire amount, and 
while comprising for the most part injurious species, include a few 
forms generally considered useful. These will be discussed at once. 
A certain family of ground-inhabiting beetles, the Carabide, on 
account of their predaceous habits, are 
usually classed as beneficial. They have been 
detected, however, feeding upon vegetable 
‘matter, and in many places even upon culti- 
vated crops. These facts should make us 
slow to condemn a bird for picking up a few 
of them. The present species manifests very 
little liking for ground-beetles, only 4 birds a ea atau gh 
of the entire number having taken them, and tai ied te. viridis). 
in no case did they constitute more than 10 eae 
per cent of the stomach contents. j 
One other predaceous insect was captured. This was a robber fly 
(Asilide). Flies of this family capture grasshoppers, beetles, other 
flies and bees, and at times do considerable mischief among honey 
bees. They are not wholly beneficial, therefore, although probably 
the balance is in their favor. If it is the rule, however, as appears 
from the present examination, that not more than 1 blue grosbeak in 
50 takes a robber fly, the resulting damage need not disturb us. 
Besides the insects of predatory habits, there are others which are 
useful as parasites. None of these were taken directly by any of the 
blue grosbeaks examined, but about 20 eggs of a parasite, probably 
a tachina fly, were attached to the body of a purslane caterpillar eaten: 
by one of the birds. Had these parasitic flies been allowed to com- 
plete development they would have attacked and destroyed other 
caterpillars, but probably not so many as the grosbeak which fed upon 
them, one-tenth of whose food would have consisted of these creatures. 
Caterpillars and adult lepidoptera (moths) compose 9.77 percent 
of the food of the blue grosbeak. The purslane caterpillar (fig. 38) 
mentioned above is eaten by adults and is fed also to the nestlings. 
