March, 1912.] DaVIS : DISTRIBUTION OF TiGER BEETLES. 17 



To attempt to define zones or regions for such a group is a hope- 

 less task for scarcely any barrier is effective for all the species, all 

 the time ; even the seas are crossed in the abundance of geologic 

 time; the best one can do is to indicate the avenues of distribution the 

 insects have followed, the sea beach, the river systems, the broad 

 valleys and plains, along which some species have travelled further, 

 some not so far, according to the adaptability of the organism to the 

 new environments it has encountered, and the accidents that have 

 assisted or retarded its progress. 

 * Such avenues of distribution have been outlined in F. M. 

 Webster's paper in Psyche on " Dift'usion " and, though reached by 

 entirely different reasoning, are not very different to those here 

 suggested. 



Turning to Mr. Harris's collection for a last look at Tcfracha you 

 may see what has happened to that genus — the most abundant of the 

 tribe Megacephalini, represented in South America by numerous 

 species, more capable of sustained flight than most, attracted to light, 

 easily spreading through the mainland of Central America to Mexico, 

 represented there by many species, with more difficulty crossing the 

 seas between the West Indian islands and there represented by fewer 

 species. Finally reaching the United States reduced to two species 

 represented by numerous individuals in our southern states but until 

 a few years ago, unknown northward. Then thanks to electric lights 

 perhaps, it became abundant in Cincinnati. Last year, by Mr. Davis's 

 fortunate capture, we learned that it had reached Long Island. 



It is by accident that every beetle in Mr. Harris's box has its head 

 pointed northward, but nevertheless it indicates, as truly as the mag- 

 netic needle indicates the pole, the direction in which these species 

 are moving. 



NOTES ON THE DISTRIBUTION OF SEVERAL 

 SPECIES OF TIGER BEETLES. 



By Wm. T. Davis, 

 New Brighton, N. Y. 



On June 28, 191 1, Mr. Ernest Shoemaker and the writer, with 

 some Washington friends, went to Chesapeake Beach, Md., in search 



