TAMARACK FOREST COMMUNITIES 195 



Ground stratum: On the sphagnum, which sometimes occurs in the 

 pools, various insects and spiders occur, including, according to Hancock 

 (40), two species of sphagnum crickets. On the higher ground numbers 

 of typical moist forest animals occur sparingly. Frogs are often numer- 

 ous. The common frogs (Rana pipiens and clamata) and the marsh 

 tree-frog (Chorophilus nigritus) occur in summer. The wood-frog and 

 Pickering's tree-frog (Rana sylvatica and Hyla pickeringii, Fig. 150) are 

 regular residents; probably both breed in the pools (139) between the 

 hummocks. Farther north the hermit thrush nests on the hummocks 

 amid the dense undergrowth. This is also the typical haunt of the 

 varying hare (Lepus americanus Erx.) (83, 142, 143), which is white in 

 winter and brown in summer; it is common in tamarack swamps farther 

 north. The lynx (p. 15) was probably once common near Chicago and 

 is most likely to have frequented these swamps. Adams (83, 42) records 

 its tracks on the hummocks of the tamarack swamps on Isle Royale in 

 Lake Superior. Judged by its tracks it wanders far. It feeds largely 

 on hares, the numbers of which fluctuate (inversely) with the numbers of 

 lynx. The otter (Luira canadensis Schr.) and Cooper's lemming mouse 

 might be added as probable former residents (143, 21). 



Field stratum : This is confined to hummocks supporting herbaceous 

 plants. Insects, spiders (159), etc., are common; some characteristic 

 species occur. 



Tree stratum: The brindled grasshopper (Melanoplus punctulatus) 

 (Fig. 146) has been found on the low branches of the tamarack and 

 deposits its eggs on the bark of the trunk or on stumps. Several other 

 insects have been recorded as common on the tamarack, among which 

 are a sawfly, an earwig (Fig. 147), a lappet moth, and a woolly aphid, 

 but we have not taken all of them. (See 137, II, 838, and I, Plate 18.) 

 The tamarack is infested by bark beetles. In the swamp at Mineral 

 Springs, Ind., we found one (Polygraphus rufipennis) (137), sometimes 

 also Dendroctonus simplex Lee, common under the bark of partially dead 

 trees (Fig. 149). The larvae of the clerid beetle (Thanasimus dubius) 

 (Fig. 148) (137) occur with the bark beetles and feed upon them. 

 The adult of the clerid (137) appears in spring, having wintered over 

 as adult or in the late larval or pupal stage. It goes about on the 

 bark of trees, seizing the bark beetles and later laying eggs at the 

 openings of their galleries. The larvae invade the galleries and feed 

 upon the eggs and larvae of the bark beetles. Felt states that two 

 other bark beetles attack the tamarack (160). In this marsh the bark 

 beetles have killed a number of trees. In summer the area of dead ones 

 may be seen a mile away. 



