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 inevidence. There are scorpion-flies (Fig. 153, 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 Theridium frondeum) 
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 (A phrophora). The unicorn 
larva (Fig. 155) (163) feeds on the leaves of the dogwood, and the sphinx 
larva on the Virginia creeper (Fig. 154a). 
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 raccoonis 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 (A griolimax campesiris) 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, 
