FAMILY SI MU LI I DM 261 



injurious pests and occasion many losses to agriculturists, 

 so that they deserve a paragraph at this point, although for 

 most of their existence they have very little in common with 

 farm life. They have had an added interest in recent years 

 on account of the effort to prove them the carrier of the 

 disease known as pellagra, but proof of such a comiection 

 is still wanting. The adults are short, small, thick-lxxlied 

 insects; the thorax especially heav\', and the humped appear- 

 ance of the whole body has given rise to the name buffalo 

 gnats. They are all small species, scarcely any of them a 

 q-uarter of an inch in length. The larv?e are distinctly aquatic, 

 usually living in swiftly running water. They are so fully 

 adapted for aquatic life that they attach themselves by 

 silken threads to submerged objects and depend for their 

 food upon minute organisms floating or swimming in the 

 water. The pupal stage is also passed under water, a thin 

 cocoon being spun upon the under side of the leaf or other 

 submergcfl object. When the adults emerge from these they 

 rise rapidly to the surface of the w^ater, the wings expanding 

 promptly, and they are ready for flight almost instantly. 

 At times they occur in enormous swarms and the females 

 are very blood-thirsty, attacking all kinds of warm-blooded 

 animals, sometimes with very disastrous results. In the 

 Northeastern States and in parts of Canada, especially in 

 Labrador, there is a species known as the black fly. They 

 occur at times in such abundance as to make it practically 

 impossible to remain out of doors, and domestic animals will 

 seek any possible shelter in order to avoid the attacks of the 

 insect. In the Southern Mississippi Valley there are two 

 common species which have been studied in detail. One of 

 these, the turkey gnat, is said to make its attacks very gen- 

 erally upon poultry, although it is not limited to these animals. 



The other species which is credited with the greatest 

 amount of loss in the Mississippi Valley region may be 

 considered somewhat in detail and as a representative for 

 the family. 



Southern Buffalo Gnat {Simulium pevnarum, Kiley). — The 

 •investigations of 1885-86-87, which have been reported very 



