A NUTRITIONAL STUDY OF INSECTS 
From the foregoing observations on Sciarid larvae, it is apparent 
that they do not spin the web or secrete the gelatinous tube which 
surrounds them, but merely become covered with the exudations 
and spores of the fungi on which they live, and these spores, exu- 
dations, and hyphae serve as food for the insect. Upon pupation 
the enveloping drop of mucilaginous material surrounds the last 
larval skin and the pupa forming a cocoon of spores from which 
mycelia grow out. If the larvae are placed on a smooth paper 
under the binocular they are unable to move their long footless 
body. The mandibles with their flat surface cannot grasp the 
small particles of fiber which do not stand out above the surface. 
If a drop of water is placed upon the larva it immediately moves 
about actively by means of a ripple of circular contraction which 
starts at the posterior end and rolls a collar of integument over 
the anterior end. The anterior end is then protracted and the 
process repeated. It is apparent that in such a method of loco- 
motion an enveloping fluid of high surface tension would be of 
great assistance. The function of the 'accidentally' accumulated 
mucilaginous envelope is twofold, first, to serve as a protection 
against evaporation and, second, to assist in locomotion. 
The larval period is about twelve days and the pupal period 
four days. Adults are very active and run about rapidly, the 
male when in pursuit of the female flapping its wings vigorously. 
Adults may be seen to eject a hard white gelatinous body com- 
posed of fungus hyphae, etc. The adults and pupae seem much 
more immune to fungus attack than Drosophila. In the pupal 
stage this protection may be due to the complete envelope of 
gelatinous substance. The female deposits several separate piles 
of light yellow spherical eggs on the medium. These likewise 
seem to be immune to fungus injury as the mold often completely 
envelops them without causing death. The development and 
movement of the embryo can be observed through the egg which 
hatches in three to four days. 
An attempt was made to sterilize the eggs and pupae, but death 
always resulted, probably owing to the soft exterior of these stages. 
The insects grew equally well on bran agar, yeast agar, and banana 
agar, feeding upon the luxuriant fungous growth always present. 
