1930 ] 
The Food of Insects 
3 
It may seem idle to speculate concerning the most primi- 
tive type of food habits among the insects, although there 
seems good reason to believe that the earliest insects, like 
their somewhat problematical ancestors, may have subsisted 
upon dead or moribund animals in combination with mis- 
cellaneous plant material, or to speak more concisely, in 
terms of human dietetics, the balanced chop suey ration 
mentioned a few moments ago. 
Such was undoubtedly the diet of the early multitudinous 
cockroaches that swarmed throughout those carboniferous 
forests. These very insects are today a prominent feature of 
the entomological fauna of tropical jungles, and, moreover, 
they have even invaded the overheated tenements of our 
great cities. The cockroaches, therefore, show three char- 
acteristic features: a mixed, more or less indiscriminate 
diet ; great morphological stability over extended periods of 
time, and an adaptability to changing conditions and to 
intensive competition with other, more modern types of 
insects. 
On the other hand, purely carnivorous habits are char- 
acteristic of several very primitive groups, notably of the 
earliest dragonflies. The predatory habits of these insects 
are very pronounced and predatism has attained a wonder- 
ful degree of perfection among the modern dragonflies. 
The imagines are admirably fitted for the capture of prey 
while on the wing, and the nymphs are even more marvel- 
ously adapted for the seizure of prey beneath the water in 
which they live. The mechanism peculiar to the nymph and 
unparalleled elsewhere is a unique, pincers-like, bristly 
organ, known as the mask formed by the highly modified 
labium. The form of this structure is so similar throughout 
the Odonata that there can be no doubt that it was char- 
acteristic of the earliest representatives of the order and 
perhaps of the ancestral Protodonata as well. So far then, 
as structural adaptation is concerned, the dragonflies must 
be rated very high. They have persisted over an extremely 
long period with little more tendency toward morphological 
change or speciation than the cockroaches. Even though 
the nymphal mouthparts are most exquisitely suited for 
the unfailing capture of prey, the diet of individual genera 
and species has not become highly specialized. We might 
