The Food of Birds. 
99 
the contents of the intestine with a microscope, and 
mounted the material for permanent preservation. These 
larvae were filled with vegetation, some of which was 
recognized as the leaves and rootlets of the grass-like 
weeds of the vicinity, while the remainder evidently con- 
sisted of the leaves of net-veined plants, probably trees, 
by which the ground was overshadowed. The frequency 
with which these tissues were found penetrated by fungi 
showed that this vegetation was in a decaying condition. 
I next looked through my notes of the contents of the 
stomachs of meadow-larks shot at the very time when 
the robins were stuffing themselves with this Bibio larva, 
and found that the meadow-larks had not eaten so much 
as one. As they search the ground more closely than the 
robin, relying almost as fully on insect food, this seemed 
good evidence that the larva occurs here chiefly in situa- 
tions frequented by the robin and not by the meadow- 
lark — that is, in gardens, groves and the like. It was only 
in such situations that I was able to find it myself. There 
is, therefore, no present evidence that this larva is now 
injurious even in the slightest degree, and the robin is 
not entitled to any very positive credit for its destruc- 
tion. There is some probability, however, that if the in- 
sect were allowed to increase indefinitely, it would be- 
come injurious to living vegetation; and if so, the high 
rate of its multiplication would make it a seriously de- 
structive pest. The immense numbers annually destroyed 
by the robin may be inferred from the fact that I have 
counted as many as one hundred and seventy-five from 
the stomach of a single bird ; and as fully half of the food 
of the robin for a month consists only of this insect, 
fifty larvae a day for each robin, or one thousand five hun- 
dred for the month, will be a very moderate estimate. 
About five per cent, of the food of February consisted 
of beneficial insects. 
March. 
Nine birds were shot on four different days of March, 
between the 9th and 31st, six of them in McLean county, 
and three at Galena. Four of these had eaten Bibio larvae 
again, which amounted to thirty-seven per cent, of the 
