MOULTING HABITS OF SPIDERS. 101 



conditions. Black wall had already noticed that food and temperature 

 exercise a decided influence, 1 and Wagner has confirmed the fact. Moult- 

 ing is suspended in winter in natural site ; but if spiders be housed in 

 warm rooms the moult may be artificially stimulated, but the 

 Modify- moulting intervals are then longer than usual in natural condi- 

 ,P , tion. If a young brood of the same age be exposed to different 

 degrees of heat they will shed their skins at intervals corre- 

 sponding thereto, the warmer ones earlier, the colder later. The lack of 

 sufficient nourishment retards the moulting epoch, and tends to make the 

 act more difficult and dangerous, so that many spiders die in or after the 

 act from inanition. 



Causes affecting the normal health of the organism modify the moult. 

 Blackwall discovered that young spiders infested by the larva of Poly- 

 sphincta carbonaria, an insect belonging to the Ichneumonidse 

 which feeds upon their fluids, never moult. 2 Wagner notes the 

 effect of the prick of a Pompilus sting upon two male Trochosas ; 

 one stung July 8th remained sick and languid until August 7th, an unus- 

 ually long period, and then moulted. During the act, probably for lack of 

 vigor, the legs were contorted and deprived of motion. Another male, 

 stung at the same time, passed an interval of a month and ten days before 

 moulting, a great retardation as compared with subjects of his own age 

 who had long before that shed their skins. This spider began moulting 

 August 17th, and on September 2d, when it was moribund, it had only 

 achieved the moult of the abdomen and corselet. The legs were with- 

 drawn from the old skin in the morning and appeared to be normal, but 

 in the evening they were bent up and flattened, doubtless the result of 

 imperfect alimentation during the two months succeeding the sting, and of 

 the imperfection of the interior moult. 



Neither of these wounded spiders made any preparation for moulting 

 by stretching supporting frames of silk lines. The normal conduct and 

 periodicity of moulting appears thus to depend upon three kinds of agents : 

 first, the interior conditions of the animal's development; second, the expen- 

 diture of the reserve for the maintenance of internal heat and locomotion ; 

 and, third, external conditions, such as heat and food. 3 



VI. 



After moulting, all spiders, old as well as young, are in a state of 

 greater or less feebleness, proportionate to the difficulty and length of the 

 act. They hang in a relaxed and helpless condition upon their proper 

 snares, if sedentary, or upon temporary scaffolds woven as supports ; one 



1 Zoological Researches, page 309. 



2 Brit. Assn. Advanct. Sci., 14th meeting, pages 70, 71. 



3 Wagner, La Mue, page 357. 



