166 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



eessiou of plant changes before the original condition is again 

 reached. In the region under observation one of the first plants 

 to invade a new area, either fertile or sterile, is the oomraon 

 sweet clover. McUiotus alba Desr., which is shown in figure 22 

 as having become established during the previous year on a 

 gravel bar. Clements (1907) gives a brief statement concern- 

 ing plant succession on flooded soils. Each srage in this series 

 of plant changes must present a related change in the chkracter 

 of animal life present. 



It is of no little importance that floods influence animal asso- 

 ciations directly without actually aftecting tither the physio- 

 graphical or vegetational environment. This is in turn, upon 

 analysis, seen to be capable of accomplishment in two ways: (1) 

 by destroying or removing fonns already in existence and (2) 

 by providing a means of dispersal, i. e., canning forms into 

 new regions. 



While the writer was collecting at the edge of the advancing 

 water he observed great numbers of subterranean caterpillars, 

 many of which do much damage to agriculture. These larvae 

 were seen to climb grass blades and weed stems to keep out of 

 the water which forced them from beneath the soil or from their 

 places of refuge at tlie surface of the soil, only to be overtaken 

 at the uppermost tip of the plant and eventually drowned. Of 

 tliirty-uine specimens taken, twenty-five were the common army 

 worms, Helioplul<i unipwicia Haworth, two were Nocfua c-ni- 

 grum Liuneus, one Prodenia ornithogalli Guenee, ten Apaiitesi"} 

 virgo Linneus, and one Apantesis phyllira Drury. 



Higher forms of animal life were affected by the floods in 

 being forced to flee. "Woodchueks, {Mannota monax Linneus) 

 were driven from their burrows to take to trees, etc., for tempo- 

 rary safety and numbers of field mice (Microtus sp. (?) were 

 seen swimming for refuge to higher points of land. "Wood (1910) 

 records having seen voles clinging to stumps above water and 

 Shelf ord (1913) speaks of mammals as climbing trees under such 

 circumstances. It is most probable that great numbers of these 

 and other mammalian forms also perished during the period of 

 inundation. Wood (1910) thinks that in spite of the fact that 

 they can swim readily, many of these small mannnals perish 

 with each flood. Russell (1898) tells of seeing the deul bodies of 

 drowned rabbits hanging in the willows on the delta of Mackenzie 

 river. 



