SEVENTEElSr-YEAR LOCUST SNODGRASS. 
385 
the tubes was loose and might have been easil}^ thus penetrated ; nor 
did they claw their way along with the large front legs in any ordi- 
nary fashion. No ; such is not the cicada's way ; and what is not an 
insect's way it will not do even if it might. The cicada pupa has 
inherited different traditions in the art of digging. To understand 
its method of work we must first study the construction of its front 
legs, for these are its principal tools. 
The front leg of the pupa is composed of the same number of parts 
as any other of its legs, as will be seen in figure 2 at ^. The third 
joint from the base, called the femur (F), is large and swollen in the 
front leg, and has a pair of large spines and a comb of shorter ones 
projecting from its lower edge. The next joint is the tibia {Th). 
It is curved and terminates in 
a strong hooked point. Finally, 
attached to the inner face of the 
tibia, well back from its distal end, 
is the slender foot or tarsus {Tar), 
which can be extended beyond the 
tibial hook when the insect is walk- 
ing or climbing, but can also be 
turned in at right angles to the 
tibia, as shown at 5, or bent back 
against its inner surface. 
Let us now return to the insects 
laboring in the tubes. The use of 
the various implements on their 
front legs will be clearly shown. 
They are using the curved, sharp- 
pointed tibiae as picks with which 
to loosen the earth, the tarsi turned back and out of the way, the 
legs working alternately. When a small pile of loosened material ac- 
cumulates a rake is necessary. This is furnished by the tarsus 
now turned inward at right angles to the tibia. A little pile is 
scraped back toward the body, and— here comes the important part, the 
cicada's specialty— the little pile of rakings is grasped between the 
tibia and the femur, the former closing up against the ventral spines 
of the latter, the leg strikes forcibly outward, and the fistful of 
loosened earth is mashed back into the surrounding earth. The 
process is repeated, first with one leg, then with the other. The 
digging cicada looks like a pugilist training on a punching bag. 
Now and then the worker stops and rubs its legs over the front of 
its head to clean them on the rows of bristles which cover each side 
of the face. Then it proceeds again, clawing, raking, gathering up 
the loosened particles, thrusting them back into the earth wall. Its 
Fig. 2. — A, right front leg of mature 
pupa, inner side (4 times natural size) : 
Cx, basal joint or coxa ; Tr, trochanter ; 
F, femur ; Th, tibia ; Tar, tarsus, with 
two terminal claws. B, Showing the 
tarsus (Tar) beut inward at right 
angles to the tibia (Th), the position in 
which it is u.scd as a rake. 
