22 BULLETIN" 329, U. S. DEPARTMENT OF AGRICULTURE. 



THE FOOD OF THE LAKV^E. 



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. 



