202 WET FOREST COMMUNITIES 



the cutworms from the field stratum, the stinkbugs and leaf-bugs from 

 the river margin, and large white-faced hornets (Vespa maculata). 



Field stratum: In early summer the forms of the field stratum are 

 most in evidence. There are scorpion-flies (Fig. 1 53, p. 200), the males of 

 which have curious clasping organs at the posterior end of the abdomen. 

 Bittacus, the long-legged insect, closely related to the former, flies about 

 among the nettles; it has the curious habit of seizing flies with its hinder- 

 most pair of legs and holding them while they are being devoured. In 

 their breeding both of these insects belong to the ground stratum. 



The harvestmen, or daddy-longlegs, are always in evidence, crawl- 

 ing over the nettles (Liobunum dorsatum and ventricosum being most 

 common) . Several spiders (Leucauge hortorum and Theridiumfrondeum) 

 occur. Numerous bugs including Reduviolus annulatus, syrphus flies 

 (Syrphus americanus), and aphids, with the various enemies which occur 

 with them, are common here. After rains we find many animals of the 

 ground stratum on the nettles and the trunks of trees. We have noted 

 the slugs (Agriolimax campestris) and the snails (Polygyra profunda and 

 thyroides) here. 



Shrub stratum: The shrub stratum is well developed. The dogwood 

 is one of the characteristic shrubs, and in early summer its leaves usually 

 are covered with small bunches of foam which upon inspection are found 

 to contain a small insect, the spittle insect (Aphrophora). The unicorn 

 larva (Fig. 155) (163) feeds on the leaves of the dogwood, and the sphinx 

 larva on the Virginia creeper (Fig. 1540)- 



Tree stratum: The tree stratum has not been especially studied. 

 The trees above the level of the shrub stratum are inhabited by many 

 borers, lepidopterous larvae feeding on the leaves, and many birds nesting 

 in the branches. The raccoon is especially fond of nesting high in hollow 

 trees of the flood-plain forest. The opossum, which was never abundant 

 near Chicago, found a suitable place in the trees of the flood-plain with 

 its wild grapes and tender herbs. Under natural conditions this is one 

 of the chief haunts of the gray squirrel, now familiar in our parks (21). 

 For birds frequenting the flood-plain, see Baker (100, pp. 476-78). 



The most striking peculiarity of the flood-plain forest is its frequent 

 inundation. In the spring of 1908 we found the flood-plain of the north 

 branch of the Chicago River inundated at a time when the nettles were 

 but a few inches high. On the small nettles we found the common small 

 slug (Agriolimax campestris) and the snails (Succinea avara and retusa) in 

 great abundance. Caught in a corner behind a tree in some driftwood 

 we found a carpenter ant (Camponotus), some flood-plain cutworms, 



