88 FOOD HABITS OF THE GROSBEAKS. 
likely to be eaten by birds, both because they are usually discolored 
or otherwise abnormal in appearance and because often they are in- 
active, and hence escape attention. It should be stated, however, that 
freshly parasitized individuals are of normal appearance, and 
whether or. not they are recognized by birds, it is certain that in the 
stomach such caterpillars can not be distinguished from the unin- 
fested. 
However, it is certain that, in spite of this difficulty of recog- 
nizing recently parasitized larvee, a well-defined tendency on the 
part of birds to avoid these doomed insects is shown by the wholly 
insignificant number found in which parasitism is evident. Only 
the one parasitized caterpillar mentioned above, and one other eaten 
by a hawk, have been found in more than 40,000 stomachs examined 
by the Biological Survey. Hence it would seem that serious diminu- 
tion in the ranks of parasites is much more logically explained by 
some other cause, such as the well-known pernicious activities of cer- 
tain hyperparasites, than by the attacks of predaceous foes. The 
following extract? from “A Study of the Hymenopterous Parasites 
of the American Tent Caterpillar,” by W. F. Fiske, serves to show the 
possibilities of this hyperparasitical activity. 
In 1896 it [the tent caterpillar] was exceedingly common, so much so as to 
attract attention all over the State, and it was consequently assumed that its 
parasites would also have increased to such an extent as to be a considerable 
factor in bringing about a more normal condition in 1897. But strangely 
enough this reasoning was found to be diametrically opposite to the facts of 
the case. In 1896 a great many caterpillars were destroyed by Limneria fugi- 
tira [a parasite], and numbers of the characteristic cocoons of this species were 
collected and bred at this station. These proved in their turn to be almost 
entirely the prey of Pimpla inquisitor [a hyperparasite], and the breeding 
cages in which the cocoons were confined becoming filled with the adults of the 
hyperparasite, it was mentioned in the report of the year, and given credit for 
the destruction of large numbers of tent caterpillars. Thus it was the Lim- 
neria which proved to be the real victim, and as its cocoons were rare the next 
year the primary host, Clisiocampa americana [the tent caterpillar], was indi- 
rectly but decidedly the gainer. ? 
AS one season’s observations succeeded another’s this case from being an 
exception, as was at first thought, was found to be more nearly the rule. The 
comparative abundance of the tent caterpillars varied greatly, it is true, but 
this was obviously due to other and distinct causes than this under discussion, 
and only a certain percentage, varying considerably from one colony to another, 
or to a less degree between different localities, fell a prey to the hymenopterous 
parasites. The parasites as a body were found to exact a certain tithe of blood, 
so to speak, and this being obtained would proceed to fight over its possession, 
passing it from one to another, from parasite to hyperparasite, until often, per- 
haps, there would be little more than enough left of a single large caterpillar 
than that sufficient to support a single small Chalcid. 
It is evident from these statements that we need look no further 
for the enemies which so check the useful services of parasites. 
a Tech. Bull. 6, N. H. Agr. Exp. Sta., 1903, pp. 185-186. 
