120 



and oxygen, the temperature, etc., is omitted for simplicity, not 

 because these matters are unimportant. Some of the main features 

 of these interrelations are summarized in the following diagram. Fig- 

 ure 1 6. This shows that the white-grubs living in the soil and devour- 

 ing the roots of plants are preyed upon in turn by an aggressive fun- 

 gus (Cordyceps) and by a wasp (Tiphia) — an external parasite; and 

 that Tiphia h parasitized in turn by Exoprosopa and by the larva of 

 the small beetle Rhipiphorus. The adult May-beetles feed upon the 

 leaves of trees, and although many show a decided preference for trees 

 living in the open, as the cottonwood and willows, others feed largely 

 upon forest trees. Thus the prairie animals exert a direct influence 

 upon the forest community as well as upon the prairie. The differ- 

 ential grasshopper feeds upon the vegetation, and jumps or flies into 

 the webs of Argiope, where it may be killed even if it should not be 

 eaten. The eggs which this grasshopper lays in the soil are devoured 

 by the larvae of Chauliognathus and Bpicauta, and the adults are killed 

 by the fungus Bmpusa,~or mutilated by the mite Tromhidium — an ex- 

 ternal parasite (PI. XXI, figs, i and 2). The rusty digger-wasp, 

 Chlorion ichneumoneum, feeds itpon the nectar and pollen of flowers, 

 and provisions its burrows in the ground for its larva with grasshop- 

 pers (Orchelimum) ; this larva, again, is probably devoured by the 

 small parasitic fly Metopia. The larvae of the soldier-beetle Chauliog- 

 nathus are predaceous, and eat other larvae ; thus they influence many 

 species; the adults frequent flowers as pollen-feeders. Although 

 Bpicauta devours eggs of grasshoppers during its larval stage it feeds 

 upon vegetation in the adult stage. The larvae of Bombus live upon 

 nectar and pollen supplied them by the female or worker, and the adult 

 is also a nectar- and pollen-feeder, Bombus thus being solely sustained 

 by vegetation. They are preyed upon by a host of predaceous enemies, 

 as Phymata and Promachus; and parasites, including the flies Pron- 

 tina, Brachycoma, probably Conops, and the false bumblebee (Psithy- 

 ru-s); their nests, moreover, form a habitation for a great variety of 

 insects, mites, and other animals too numerous to be put in the dia- 

 gram. These bees, then, on account of their large size, their large col- 

 onies, and the large amount of concentrated food which they amass at 

 the nest, combine to make themselves attractive to a great number of 

 animals, and become the hub of a busy microcosm, an extensive com- 

 munity of mutually interrelated kinds. 



The root-louse of grass, Schisoneura panicola Thos. (Forbes, '94, 

 pp. 85-93), through the attention of several kinds of ants, Lasius niger 

 americanus Emery, L,. flavus De G., L. interjectus Mayr, and Formica 

 schaufussi Mayr, is cared for from the tgg to the adult stage; these 

 ants keep the plant-lice on fresh roots from which they suck their food. 



