THE RED SPIDER ON COTTON. 9 



material difference iii the lengtli of the joints such as develops in the 

 later stages. The patella? and tibiae are only slightly longer than wide. 

 The onychiuni, which m the adult becomes conspicuously attenuated, 

 appears as a mere abrupt narrowmg of the tarsus in the larva. The 

 larval palpal characters agree very closely with those of the adult, 

 except that the terminal ''jEinger'' 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 

 larvse give the foUowmg 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 n^inphal stages) exhibits an active period and a resting 

 period. The resting stage in South Carolina requires but a few hours 

 for its completion. In 1 898 Von Hanstein designated this resting 

 stage by the term " NymphochrysaUis," which he states lasted from 

 24 to 30 hours at Berhn. 



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 th(^ body. This accomplished, the free legs are used to pull 

 with, and by means of a twisting, wTiggling movement the nymph 

 extricates legs III 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 sitv. 

 'ITk' fourth pair of legs, which become evident with the completion 

 of the larval molt, at first appear atrophied and usek^ss, but in a very 

 ff'W minut(\s the nymph acquires use of its new appendages. 

 r,4:'.wt- I'.iiii. lie. 17 2 



