100 ‘THE PERIODICAL CICADA. 
trunks was quite audible, particularly vigorous pup ascending the trees to the 
height of 30 feet. 
Plate V, showing empty pupal shells clinging to leaves, still further 
illustrates the large number of these insects which often emerge. 
As noted by Mr. Farmsley, of Louisville, Ky., the cicadas do not 
appear very numerously on tops of mountains within an infested area, 
but gradually decrease in numbers as one ascends, the greater scarcity 
being noticeable both to the eye and the ear, the rattling chorus 
growing less and less strong. 
On the authority of Dr. Hopkins, the diminishing of the Cicada in 
numbers as one ascends to higher elevations is apparently not always 
true. Dr. Hopkins describes driving for a day through the Cicada 
district of West Virginia in 1897 on the occasion of the reappearance 
of the 17-year Brood V, and states that as he approached the eastern 
Fic. 40.—Exit holes of the periodical Cicada at surface of soil. The rule shows the large number o! 
holes occurring, in this instance, in a square foot of ground 
borders of Preston County the cicadas became more numerous, and 
as the mountain west of Cranesville was ascended the Cicada was 
found, at an elevation of 2,600 to 2,800 feet, to occur in far greater 
numbers than at any point previously traversed. The leaves and 
twigs of the trees were literally covered with the insects, and the twigs: 
were bending from their weight. This point seems to have been the 
eastern border of the swarm, and a few rods farther up the cicadas 
became very scattered and soon ceased altogether. 
They often also appear in greatest number in rather well-defined 
districts within the general range of the brood, or, in other words, 
are irregular in local distribution. This variation in abundance is 
due in some cases to differences in the character of the soil and in 
others, perhaps, to varying surface conditions, as of timber growth, 
etc. They prefer, apparently, white-oak groves, and are most abun- 
