THE RED SPIDER ON COTTON. 9 
material difference in the length of the joints such as develops in the 
laterstages. The patellx and tibiz are only slightly longer than wide. 
The onychium, which in the adult becomes conspicuously attenuated, 
appears as a mere abrupt narrowing of the tarsus in the larva. The 
larval palpal characters agree very closely with those of the adult, 
except that the terminal ‘‘finger”’ of the ‘‘thumb”’ seems relatively 
more slender. The larval body bristles are proportionally shorter 
and stouter than in the adult. A large series of measurements of 
| larve *give the following dimensions: Length, 0.151 mm.; width, 
0.116 mm. 
Length of larval instar.—The time required for the completion of 
the larval stage is subject to considerable variation, mainly attribu- 
table to temperature and moisture conditions. The larva is much 
less resistant to adverse minimum temperatures than the egg. While 
in summer this stage rarely requires more than 2 days, in the early 
spring and late fall records as long as 15, 16, and 17 days are fre- 
quently obtained. From data derived from 61 colonies we have 
computed the average interval between hatching and the first molt 
to be 1.94 days. Basing his computations on 6 completed records, 
Ewing (1914) states that the average larval period at Corvallis, Oreg., 
is 3.33 days. Perkins (1897) found 4 days to be the average time 
required in Vermont for the completion of this stage. 
As has been recorded by a few other workers, the larval stage (as 
well as the nymphal stages) exhibits an active period and a resting 
period. The resting stage in South Carolina requires but a few hours 
for its completion. In 1898 Von Hanstein designated this resting 
stage by the term ‘“‘ Nymphochrysallis,’ which he states lasted from 
24 to 30 hours at Berlin. 
Molting.—The five cases of molting observed occupied from 2 
minutes to 4 minutes 20 seconds. The operation is initiated by a 
brief series of struggles which result in the partial rupture of the 
skin at the line of the postcephalothoracic suture. The separation 
is complete over the back and extends laterally down either side, so 
that the two halves of the old skin are merely connected by a ventral 
strip. The primary nymph disengages its forelegs and anterior por- 
tion of the body. This accomplished, the free legs are used to pull 
with, and by means of a twisting, wriggling movement the nymph 
extricates legs ITT and IV and walks out over the front portion of the 
cast skin and is entirely free. The exuvium, as a rule, is left in situ, 
The fourth pair of legs, which become evident with the completion 
_-of the larval molt, at first appear atrophied and useless, but in a very 
few minutes the nymph acquires use of its new appendages. 
51380-- Bull. 416—17-__2 
