KEPOBT OF THE BUREAU OF ANIMAL INDUSTRY. 457 



whose life during its adolescent stages is so thoroughly dependent 

 upon the current of a stream, should select as its home those streams 

 whose sluggish movement is 6nly broken at intervals by shoals or 

 jams of logs and other vegetation, is rather surprising, until we find 

 that the food supply of the larvae is nearly, and perhaps exclusively, 

 confined to alluvial streams. Although these larvse are strictly 

 aquatic, they can only make their way with difficulty in the water in 

 search of food, and must remain, to an extent, stationary, and secure 

 only so much sustenance as the current brings within their reach. 



ADULT GNATS. 



These make their appearance annually, in greater or less numbers 

 throughout their breeding grounds, from about the 20th of February 

 until the 10th of May, the season of greatest abundance, in extremely 

 favorable years, being from March 20 to May 1. Often, however, this 

 period of extreme abundance is reduced to a week or ten days, but 

 on the other hand, a very few will probably be found as late as 

 August 1, as I observed full-grown larvse and pupae only a few days 

 prior to that date. 



The adults which make their appearance first are much larger 

 than those coming later, and it is the former to which the greater 

 portion of the destruction of stock is due. This is the Simulium 

 pecuarum, which Dr. Riley has described and figured (Report of the 

 Commissioner of Agriculture, for 1886, p. 512, Plate VIII, Figs. 1, 2, 

 3), and is the true Buffalo gnat. These are soon joined by several 

 other forms, which may or may not prove to be distinct species. The 

 Turkey gnat, S. meridianole, Riley (loc, cit.,p, 513, Plate VIII, Fig. 

 4), and another undescribed form will, however, probably prove to 

 be valid species. 



These adults emerge from the pupte beneath the surface of the 

 stream, and the number which win develop in a very limited area is 

 simply astonishing As soon as they leave the water they betake 

 themselves to the bushes and other vegetation about and overhang- 

 ing the stream, and remain there until nightfall, when they move oft 

 or are driven away by the winds, and appear suddenly and without 

 warning in localities far distant from their breeding places. So im- 

 mense are their numbers that for weeks the vegetation in the vicinity 

 of these breeding places will be black with them each evening, and 

 these numbers are replaced again, day after day, until one will almost 

 wonder that the stream could have held them all. This nomadic 

 habit, however, only appears in the females, and males are found 

 away from the locality where they originate only in isolated cases, 

 the mouth parts of this sex being so constituted as to effectually pre- 

 vent the sucking of blood, thereby rendering them harmless on that 

 score. The blood-sucking gnats, then, are all females, and in the 

 case of the larger and most venomous, these females seem to be ster- 

 ile, or, at least, there is no indication that they over deposit eggs. 

 Egg-laying females of S. pecuarum, and also of at least one other 

 species, have been observed, and one of them was observed oviposit- 

 ing in great numbers. 



PLACE AND METHOD OF OVIPOSITION. 



In all cases where female Simulium were observed in the act of 

 ovipositing, they selected some locality where the current was not 



