NATURE OF LAEVAL FOOD 287 



The first yellow-fever commission to Vera Cruz found that, on account of 

 this habit, the larvae are not easily disposed of by pouring out the contents of ^a 

 barrel. '' When the barrel or other container with thousands of larvge is ap- 

 proached and slightly agitated, the insects disappear rapidly to the very bottom, 

 so that nearly all the water can be dipped from the barrel without removing 

 more than a few of the larvae. The barrel may be turned upon its side, and it will 

 be found that about 80 per cent of the larvas will stay in the few remaining 

 ounces of water." 



FOOD-HABITS OF THE LARV^. 



It has been pointed out that the larvae occur most frequently in the clear 

 water in rain-water barrels or in drinking-water receptacles in houses. The 

 water in such receptacles contains more or less animal matter, such as particles 

 of human skin or remains of insects, as well as vegetable refuse, and such 

 probably is generally the food of the larvae. The larvae feed at the bottom, where 

 they mouth over the organic sediment, even when the water is very deep. Larvffi 

 in confinement may be observed chewing vigorously at dead insects or larval and 

 pupal exuWffi. 



C. S. Banks has observed the larvae in the Philippines and says : " They feed 

 largely upon the sediment contained in the dregs, which may be both animal 

 and vegetable in its character, but more frequently vegetable, as it is composed 

 of the bits of decaying nipa forming the roofs from which the rain water is 

 collected. The larvae, in feeding, move forward over the bottom of the vessel, 

 taking in the particles of food with great rapidity and rejecting tiny morsels of 

 undesirable material in a constant stream." 



Goeldi found that the larvae of calopus are cannibalistic, and this has been 

 confirmed by the Brazilian observers at Rio de Janeiro, who state that the larger 

 larvae devour the smaller ones. This habit probably accounts for the develop- 

 ment of the larvae in very clear water, which has been so frequently noted. 



An interesting fact is that the growth of these larvae is greatly hastened by the 

 presence of a small amount of fecal matter in the water. Eeed and Carroll, at 

 Havana, found that calopus bred in the tin cans used for carrying away human 

 excrement and throve remarkably under those circumstances. 



Dupree and Morgan, of Baton Rouge, have also recorded the fact that by 

 adding fecal matter to the water they hastened the development until the life- 

 cycle was completed " in from six to eight days." 



The French commission to Rio de Janeiro found that the larvae develop in 

 clear water, but also thrive in foul water. Water containing alimentary debris, 

 amylaceous or fatty material seems to suit them perfectly. These investigators 

 thought that rain water, on account of the microbes which it contains, seems to 

 be more favorable to their development than spring water. In the laboratory the 

 larvae were easily reared in water in which had been placed excremental pellets, 

 or grains of com or wheat. They seemed to be less at ease in muddy water and 

 in water containing macerated dead leaves and vegetable debris, but they found 

 that the differences in the duration of the different stages of larval evolution in 



