PARASITES OF SIMULIUM LARVAE 87 
From no other locality in North America have these, or sim- 
ilar parasites, been recorded. As mentioned earlier in this paper, 
Simulium larvae have been carefully and extensively studied in 
several sections of the country, notably at Ithaca, New York, 
and in Maine, but in none of these places has a single case of 
parasitism been recorded. It is evident, as will be seen from the 
illustrations of parasitised larvae, that such individuals could 
hardly escape the eye of the observer, especially as, in streams 
in which infection is heavy, the greatly distended and whitened 
larvae can be readily seen from a distance of several yards from 
the water. We thus have evidence, though by no means con- 
clusive, that these parasites are not widely distributed through- 
out the United States. Other evidence is found in the fact 
that in this neighborhood the black flies are not a serious pest, 
although the nature of the country is eminently suited to the 
requirements of their larval life. In surrounding states, in every 
direction, these flies are not only a great nuisance, but also a 
dangerous pest. The southern states, especially, suffer from 
these blood-thirsty flies. In the interesting report of Professor 
Lugger, of the University of Minnesota (’96), it is stated that 
in the State of Tennessee alone, these flies were responsible, 
in the year 1892, for the loss of $500,000, through their attacks 
on cattle. But their ravages are not confined to the southern 
states, for in the northern state of Maine, and in New Brunswick, 
one hears of the death, of animals due to the attacks of these 
flies, while in the same localities it is impossible at certain seasons 
of the year to enter forests, unprotected, in the neighborhood 
of streams. It would therefore seem that we owe our deliver- 
ance largely, if not entirely, to the fact that a large percentage 
of these flies is annually killed off before maturity. 
I have made no experiments upon the transference of these 
parasites from one Simulium species to another, but, as far as 
can be seen, there should be no difficulty in accomplishing this, 
for in all cases observed the parasites infected all species of larvae, 
present at that time, in the stream where the former occurred. There 
is, however, a seasonal variation of parasitism, for the species 
found in the spring were not retaken in the fall, and vice versa, 
