
856 THE AMERICAN NATURALIST. [VoL. XXXVI. 
CAUSES OF DISTRIBUTION. 
The waves of the lake wash up great quantities of refuse, 
among which are numbers of insects. These animals may be 
either land or water forms; if the former, they have either 
come directly upon the shore, or have flown lakeward or been 
blown by an off-shore wind, and then been washed in, dead or 
dying. On account of the lake current moving southward 
along this region, specimens collected at Chicago may have 
come from points farther north (13). To this group of 
stranded land forms belong the ladybirds (Coccinellidz), 
Chrysomelidze, leaf-eating Scarabzidz and Carabide, possibly 
the Elateride, Lucanide, and the Rhyncophora among the 
Coleoptera, the Lygæidæ and Pentatomide among the Hemip- 
tera, the Hymenoptera, Neuroptera, Trichoptera, and Lepi- 
doptera, — all of which are herbivorous. Also to this group 
belong some predaceous carabids and one roach. To the 
stranded water forms belong Benacus griseus, Hydrophilus 
triangularis, and two other water beetles. 
These stranded forms may revive and depart, may serve as 
food for predaceous forms, or, if dead, fall to the share of the 
scavenger insects. The flies and ants are undoubtedly scav- 
enger forms, and inhabit this region on account of the food 
supply. In this class I would also place a small carabid beetle 
(undetermined) which occurred for a while in great numbers 
under stones and débris, so as to preclude the idea of its hav- 
ing been stranded during migration. Several small beetles 
seem to have this scavenger habit ; for example, three Staphy- 
linidze, some Scarabzeidze, and several Carabidae. In this latter 
family we find some predaceous forms which seem to inhabit 
this region normally, to feed on the dying insects or on their 
destroyers ; for example, several black forms (undetermined) 
and Galerita janus. The spiders are also predaceous, and feed 
on the flies, ants, and other small living insects. I might 
add that birds come in as a final factor and eat these various 
forms. 
