192 WET FOREST COMMUNITIES 



The insects feeding on the leaves are numerous on all the trees. The 

 following are common to the three trees mentioned (137): the cater- 

 pillars of the hickory tussock-moth, the American dagger-moth, the forest 

 tent caterpillar, the white-marked tussock-moth; each has a preference 

 for one of the trees. The larvae of several other common moths occur 

 on two of the trees, a few are confined to one. Beetle and sawfly larvae 

 also attack the leaves. Each tree has its characteristic gall insects and 

 galls; for example, on the elm, the coxcomb gall (Colopha ulmicola Fitch), 

 on the ash, the midrib gall (Cecidomyia verrucicola O.S.). These are 

 believed to be confined to particular tree species. 



According to Wood (21) such forests are the chief haunts of the gray 

 squirrel. The green heron is especially likely to nest on the low trees 

 of such a forest if they are near water. 



2. OTHER TYPES OF SWAMP FOREST COMMUNITIES 



The swamp forest formation is well developed in the Skokie marsh 

 area. We have visited these woods at a point west of Dempster Street, 

 Evanston. This was originally characterized by trees very much larger 

 than those at Wolf Lake. The soil at Wolf Lake is sand, while that at 

 Evanston is clay, which is probably more favorable for trees. However, 

 the most important cause of the greater luxuriance is greater age. 

 The subterranean stratum has not been studied. 



The ground stratum: Here we find, in addition to those species 

 of the temporary ponds at Wolf Lake, a snail (Aplexa hypnorum Linn.) 

 which is characteristic of very transient ponds (100). 



On November 27, 1903, the condition of the animals of this stratum 

 was noteworthy. In the lower moister parts of the wood we found the 

 mollusks, especially Pyramidula alternata, in groups under logs. One of 

 these groups contained 1 2 individuals. Under another log was a group 

 of about 50 ground beetles (Platynus sp.). Under one small piece of 

 bark were found three ground beetles, three rove-beetles, one slug, and 

 two snails. Under another, one tetrigid or grouse locust, several ground 

 beetles, and a rove-beetle. Under the bark of a log on the above date 

 we found the hibernating parasitic hymenoptera (Ichneumon extrematatus 

 Cress., galenus Cress, and mendax), also a queen white-faced hornet 

 (Vespa maculata), which with its colony builds a large spherical nest 

 in a tree in summer. 



Most noticeable of all was a group of several hundred small blue 

 chrysomelid beetles (Haltica ignita Illig.). They were under the leaves 

 at the base of a tree down the sides of which individuals of the same 



