412 
Journal of Agricultural Research 
Vol. XXI, No. 6 
the individual larvae and noting the number of pairs of mandibles. Five 
pairs of mandibles, gradually increasing in size (PI. 76, A-E), were thus 
found, seeming to give definite proof of the accuracy of the observations. 
As soon as the young larva hatches, it pushes its head out of the egg¬ 
shell (Pi. 75, B) and immediately begins to feed. It often feeds thus for 
about 24 hours before it completely extricates itself from the shell. In 
this stage it often feeds with only its head touching the host. It appar¬ 
ently slashes away with its mandibles until it has made a slight incision 
in the body wall of the h ost, whereupon it begins to suck up the body 
fluids. The larva feeds almost continuously, if undisturbed, until nothing 
remains of the host larva but the empty skin. When the parasites are 
very abundant, very often several eggs are found in a single jointworm 
cell, but never more than one larva completes its development therein. 
The largest and strongest larva evidently overcomes and destroys the 
others. In moving forward over its host the tip of the abdomen of the 
parasitic larva is touched to the surface of the host, where it adheres. 
It seems to function as an anal proleg and to enable the larva to bow 
the body upward. Simultaneously each segment moves forward as far 
as possible, and the sucker-like mouth is touched to the surface of the 
host, where it adheres and acts as an anchor by means of which the larva 
pulls the body forward. By alternating these movements the larva is 
enabled to move over its host with comparative ease. 
Just before each molt the body of the larva is considerably larger than 
the head. This fact enables one to determine with a fair degree of accu¬ 
racy when the larva will molt. This character is much more apparent 
in the early stages. The later stages are indicated more clearly by the 
increased number of setae. The duration of instars, as is common with 
most insects, varies with the temperature, hot weather accelerating and 
cooler weather retarding development. The first instar lasts from one 
to four days; later instars approximate this period of time, varying 
directly with temperature and the condition of the host. 
Larvae of this species which were reared in glass cells became full- 
grown in from 6 to 24 days. One hundred and thirty-seven larvae 
observed for this purpose at various times during the breeding season 
became full-grown within an average of u days. 
During the season of 1917, 41 larvae became full-grown in glass cells, 
but died during the winter before any of them pupated. In 1918, out of 
more than 100 larvae, which became full-grown in glass cells, only 9 
pupated during the same season. Those that pupated did so within a 
period of from 4 to 17 days after they had completed feeding. These 
individuals were of the first and second generations. Sixteen adults 
emerged from the remaining material, and several others pupated. 
Both first- and second-generation larvae completed development the fol¬ 
lowing spring. Five of this group were kept in the laboratory, and the 
remaining larvae were kept in a cellar during the winter. Cage material 
