460 



Larvae that were brought to the laboratory from the reservoir for 

 the supply of city water to Champaign, were subjected to a test by 

 means of freezing. Specimens that were placed in a shallow dish con- 

 taining but a small quantity of water were frozen solid by exposure 

 over night and never recovered, while those that were put in a larger 

 container, and were therefore not so completely frozen, survived in the 

 great majority of cases. This test was made in order to ascertain 

 whether, like many larvse and pupae of other orders, this species could 

 withstand freezing, and the conclusion, though based on rather meager 

 data, was that the larvae could not survive complete freezing. It seems 

 possible, then, where two tanks are available for alternate use, to rid 

 city drinking-water of these larvae in cold winter weather by drawing 

 off all the water from the infested tank, and not replenishing it for five 

 or six days. As the larvae invariably live in cases fastened to the sides 

 of the reservoirs or burrow in whatever detritus may be on the bottom, 

 and are seldom found free in the water, probably but few would be 

 drawn off in the operation of emptying the reservoir. The same ex- 

 pedient of emptying reservoirs, alternating between tanks every five or 

 six days, would, I am sure, in summer prevent the species from breed- 

 ing in these receptacles. Imagines of the species which have been ob- 

 tained from the city water here are of general occurrence throughout 

 the year from April to December, their life cycle in summer occupying 

 about thirty days. As from four to six days are passed in the egg 

 stage, if a reservoir were emptied often during the warmer period of 

 the year, allowing the inside to become thoroughly dry and thus 

 destroying the eggs and killing the larvae, it is possible that the species 

 could be exterminated where two tanks are available for alternate use. 

 It is, however, necessary to indicate that the same species may occur 

 in almost any body of water, clean or polluted, and, in the imaginal 

 stage, travels for considerable distances, accordingly, measures for 

 protection in order to be successful must be carried on without inter- 

 mission during the breeding period. From the first of December to 

 the last of March danger of infestation is remote in this latitude ex- 

 cept in unusually mild seasons. 



The presence of larvae of Chironomidcc in water affords no crite- 

 rion by which to judge of its purity or impurity. They may be found 

 in water that is perfectly safe for drinking purposes, since it usually 

 contains sufficient minute vegetable organisms for their food ; and, 

 finding this, they seem to thrive also in water which is absolutely unfit 

 to drink. The presence of larvae in any body of water simply signifies 

 that it affords them suitable conditions for life and growth. 



