PARASITES OF SIMULIUM LARVAE 89 
infection through the ova. Krassilstschik (’96) found that the 
spores of N. bombycis (pébrine) could pass through the intestines 
of birds and be still capable of infecting silkworms. This may 
also be the case with these spores, since many must be ingested 
by birds which drink at the streams. Other insects, frogs, etc., 
may also carry the spores upstream. Perhaps also, Simulium 
larvae themselves move about more than is generally believed, 
and as stated in my previous paper (’11), parasitised larvae are 
more active than healthy specimens. It may be, therefore, that 
such larvae occasionally travel a considerable distance up stream 
before death, and thus prevent the disease from being washed 
out of the stream. 
I found no definite signs of Mermis during the fall of 1911 
although, in one or two dissections of S. bracteatum, I found 
minute worms, measuring about 204 among the masses of G. 
bracteata contained in these larvae. This Mermis should also 
prove of good economic value, since there can be little doubt 
that it is a general parasite which could be readily transferred 
from one species to another. 
SUMMARY 
Although the country in the vicinity of Boston is eminently 
adapted to the breeding requirements of black flies (Simuliidae), 
they do not occur in sufficient abundance in this neighborhood 
to constitute a dangerous pest, er even a serious annoyance. 
Black flies or ‘buffalo gnats,’ are most destructive in the southern 
states, as an example of which Tennessee may be cited, where 
in one year the cattle-raisers suffered a loss of $500,000 through 
the attacks of these insects. Their ravages are not, however, 
confined to the southern states, for in the more northern states, 
as in Maine and Wisconsin, these flies, at certain seasons of the 
year, are extremely abundant, and are very injurious to stock. 
It would thus seem that in the neighborhood above named the 
comparative freedom from annoyance by these small, though 
vicious, flies must be due to some other cause than climatic 
conditions. An examination of the larvae in the small streams, 
which occur so frequently in eastern Massachusetts throws some 
