DISTRIBUTION OF TIGER BEETLES. I I 



The relation of the distribution of Cicindela to the succession of 

 plant societies has been especially studied in the vicinity of Chicago. 

 The area which affords the basis of this study is to be found at the 

 south end of Lake Michigan. Conditions here since glacial times 

 have led to the deposition of large areas of sand, which in the 

 eastern portion of the field of deposit, is stretched over an area of 

 several miles wide. At the point where most of the studies have 

 been made there is a series of ridges v/hich were originally thrown 

 up under water and later added to by aerial deposition. These 

 ridges are separated by long depressions, most of which contain 

 water. The structures are accordingly arranged in a horizontal 

 series, the oldest being, of course, furthest from the lake, and 

 differing from the younger only in age, and in being a little less 

 exposed. 



A definite succession of plant societies has been worked out by 

 the plant ecologists (Cowles and Clements) and this succession is 

 due largely to the conditions necessary for the germination of the 

 seeds and growth of the seedlings of the different plants. In forest 

 development, before the climax stage is reached, the seeds of the 

 trees comprising a given stage do not germinate and their seedlings 

 do not develop in the shade of the forest then present. Each stage 

 accordingly prepares for another and more mesophytic type. The 

 trees of the climax stage of eastern North America, the beech and 

 the maple, produce seeds that will germinate in that forest's own 

 shade. Accordingly the beech and maple will last indefinitely. 



Not all of the conditions herein described occur in the hori- 

 zontal series at any one point, but all are to be found within 

 sandy areas near Chicago. 



Let us start with the strip next to the water's edge, the very 

 youngest deposit. It is frequented by the adults of C. cupras- 

 ce/is and hirticollis. The larvae of the latter are sometimes found 

 here, but more frequently a little further back on the low, wet 

 places on the beach. Other ridges are seen to be formed beneath 

 the water and this margin is accordingly potentially the first 

 depression. 



On the lakeward side of the first ridge, among the young cot- 

 tonwoods, we find the larvae of lepida, the white tiger beetle. On 

 the leeward side where bunch-grass has come in and the cotton- 



