44 AMERICAN SPIDERS 



Then the legs are freed in slow stages by the usual rhythmical con- 

 tractions, the front ones coming out first and finally the posterior 

 pair. By the time this is accomplished, the abdomen is virtually 

 freed and the spider is suspended in the air by the thread from its 

 spinnerets. The whole process requires ten or fifteen minutes, the 

 length of time apparently being governed by the size of the spider. 

 Young spiderlings suspend themselves, molt, and lengthen their legs 

 in less than half an hour, the molting itself often taking only three 

 or four minutes. Half-grown spiderlings require about an hour, and 

 young males and females in the last molt about two hours. Molting 

 may proceed during either day or night, and seems not to be lim- 

 ited by time as are many other activities of spiders. 



The freshly molted spider is much paler and softer than in the 

 previous instar, and only gradually hardens and darkens its new 

 integument. During this relatively brief period occurs all the in- 

 crease in size of the carapace and appendages until the next molt. 

 Size increase is usually progressive and is determined by the instar 

 and the sex of the spider. In some species the legs increase tre- 

 mendously in length between the instars. Growth commences as 

 the legs are pulled out of the old integument much as fingers are 

 pulled from a glove. It continues during the time the spider is free 

 of the cast skin and hangs suspended. The appendages are bent back 

 and forth in a regular ritual. Pierre Bonnet has demonstrated with 

 some very ingenious experiments the necessity of these calisthenics 

 following the molting. Without such bending movements the ap- 

 pendages become sclerotized even at the joints and remain stiff. 



The number of molts necessary to attain maturity varies widely 

 in spiders. Bonnet has shown rather conclusively that size is the de- 

 ciding factor in most species. Tiny species molt few times, whereas 

 large ones molt a greater number of times. Bonnet noted that small 

 species of 5 or 6 mm. in length (Pholcus phalangioides, Uloborus 

 plumipes, etc.) molted four or five times. Species of medium size, 

 measuring about 8 to 1 1 mm. (Aranea diadema, Pirata piraticus, 

 etc.), molted seven or eight times. The larger spiders, 15 to 30 mm. 

 in length, molt ten to thirteen times (Dolomedes plantarius, Nephila 

 madagascariensiSy etc.). The largest of all spiders, the tarantulas, 

 molt even more often: according to Dr. Baerg, twenty-two times 

 for the male of Eurypelma californica. Further, in these spiders 

 various postnuptial molts make it probable that the females molt 

 between thirty or forty times before they die. At the lower limits, 

 only four molts are credited by Bonnet to the male of Nephila 



