THE PERIODICAL CICADA 



surface. A good idea of the size and shape of these cham- 

 bers may be obtained by filling the opened holes with a 

 mixture of plaster of Paris in water, letting the plaster 

 harden, and then digging up the casts. Figure 115 shows 

 casts of a number of chambers made in this way. Some, it 

 is seen, are mere cups about an inch in depth, but most of 

 them are long and narrow, descending several inches into 

 the ground, the longest being six inches or more in depth. 

 The width is usually about five-eighths of an inch. All 

 the chambers have a distinct enlargement at the bottom, 

 and most of them are slightly widened at the top. The 

 upper wall of each is separated from the surface by a 

 layer of undisturbed soil about half an inch in thick- 

 ness, which is not broken until the insect is ready to 

 emerge. 



The shafts are seldom straight, their courses being 

 more or less tortuous and inclined to the surface, as the 

 miner had to avoid roots and stones obstructing the 

 vertical path. The interior contains no debris of any 

 kind, and the walls are smooth and compact. Below 

 each chamber there is always evidence of a narrower 

 burrow going irregularly downward into the earth, but 

 this tunnel is filled to the chamber floor with black granu- 

 lar earth. The burrows examined by the writer near 

 Washington in 19 19 were dug through compact red clay, 

 and the lower tunnels here made a distinct black path 

 through the red of the surrounding clay, where some 

 could be followed for a considerable distance. The black 

 color of the earth filling the tunnels was possibly due to 

 an admixture of fecal matter. 



The chambers, as we have noted, are closed at the top 

 until the cicada is ready to emerge. The largest chambers 

 are many times the bulk of the nymph in volume, and it 

 becomes, then, a question as to what the insect does with 

 the material it removed in making a hole of such size. It 

 seems improbable that it could have been carried down 

 into the lower tunnel, for this would be filled with its own 



[189] 



