NORTH AMERICAN GEOTRUPINAE — HOWDEN 303 



along with an egg of Geotrupes. After hatching, the larva began feed- 

 ing on the leaves without any hesitation, feeding on any part of the 

 leaf it encountered, vein and all. All the specimens he treated in this 

 way were reared to normal-sized adults. Fabre then elaborated upon 

 this experiment by taking a dead-leaf-feeding Cetonia grub and rearing 

 it successfully on cow dung. The implications in Fabre's work on 

 adaptability of various insects to then' food and even the fundamental 

 similarity of the seemingly different materials have been neglected by 

 subsequent investigators. 



I found several cases that substantiated Fabre's findings. Geotrupes 

 splendidus adults, when put in a cage containing only cow dung, con- 

 structed a few larval cells using the dung; when put in a cage contain- 

 ing both dung and dead leaves, they used only the dead leaves. The 

 larvae feed indiscriminately on the food at hand. From this it seemed 

 that not only did the larva develop on different foods, but the adult 

 habits were not as inflexible as has formerly been believed. 



This same flexibility of habit was noted to a lesser extent in Geotrupes 

 blackburnii. The larval food provided by the adults in the rearing 

 cages consisted of cow dung, even though leaves were in the cage. 

 Larval cells of blackburnii found at Faison, N. C, seemed to be at least 

 partially composed of dead leaves and grass, but, as much of the cells 

 had already been consumed by the larvae when they were discovered, 

 the major component of the cells, whether dung or leaves, could not 

 be determined. 



The above remarks on variability of food utilization should be kept 

 in mind while reading the subsequent discussion on the habits of the 

 American species of Geotrupes, as future investigation may indicate 

 an even wider variation in food and other habits than is at present 

 known. Considerable interspecific variation has been found in the 

 time of oviposition, length of life cycle, and depth and type of burrow. 

 While known larval morphology differs, several structural and devel- 

 opmental characteristics are common to all species. AU of the eggs 

 found, while differing slightly in size, are yellowish white, elongately 

 oval, and wider near one end. Plate 14, figure 2, showing an egg of 

 Geotrupes blackburnii, illustrates these characteristics. The eggs of 

 the European species have been described as having the same general 

 elongately oval shape. After hatching, initial larval development 

 usually is quite rapid, taking perhaps a month for each of the first two 

 stadia. In the species studied, the development of the third instar 

 took much longer. The minimum time noted was about three months 

 in the case of blackburnii and splendidus. The third-stage larvae of 

 hornii overwinter, taking a much longer time to complete their devel- 

 opment. Adult emergence from the larval cell occurs largely in the 

 summer and fall. 



