22 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 
THE FOOD OF THE LARVAE. 
The food of the larvae is entirely microscopic. There are various 
accounts given on this subject by different authors, and they are 
somewhat divergent. Riley says that they feed on animalcules, but 
do not disregard microscopic matter of vegetable origin. He also 
states that larvae kept in a jar were seen to swallow the minute larval 
forms of small crustaceans belonging to the Copepoda and Isopoda, 
and that a number of square diatoms, joined together in chains, were 
found in the alimentary tract. 
Miall says that he has found in the alimentary tract flinty valves 
of diatoms, desmids, and pieces of small crustaceans. 
Kellogg, in his article on the food of Simulium and Blepharocera, 
states that he found thousands of tiny siliceous shells of diatoms in 
the intestines. They caused considerable difficulty in the making of 
microscopical sections for histological study. He also states that the 
larvae feed on the stalked Gomphonema and occasionally on the 
genus Nitzschia. They are also stated to feed on Vaucheria and 
Nothrix. 
The writer has found that the color of the larva varies according 
to the nature of the stream, and that the larvae seem to thrive best 
in streams containing the largest proportion of such organisms as 
Euglena viridis and Spirogyra. Larvae in running water were ob- 
served feeding in specially constructed glass tanks, and were seen 
to reject large Paramoecia and apparently anything except the 
smallest particles of the plankton. A striking fact seemed to be 
the effect of different foods upon the color of the larvae. When the 
tank containing the food of the larvae was filled only with water, 
decaying vegetable matter, and living grasses, the larvae became 
emaciated and starved to death; but on the introduction of green 
algae and Spirogyra, they regained their vitality and the alimentary 
tract changed from a light brownish yellow to a bright green. Dis- 
sections of the alimentary tract showed normally a quantity of green 
rod-like algae, flinty shells of diatoms, and some minute star-shaped 
animalculae. The larva of Simulium pictipes, which lives in the 
larger streams, has the alimentary canal filled with a quantity of 
sand; and the color is always brown corresponding to the brown 
growths on the rocks. The streams in South Carolina, which were 
contaminated by chemical refuse from the cotton mills, were abso- 
lutely free from larvae, and this fact is of economic importance as it 
may be utilized further in the control of the larvae. Pure animal 
sewage is not deleterious to the growth of the larvae, provided the 
other environmental factors are favorable. 
