42 AMERICAN SPIDERS 



MOLTING 



At rather definite intervals in its development the spider casts 

 off the bonds of its stiff outer covering and readjusts itself for 

 life in a more advanced stadium. This molting, or ecdysis, is 

 characteristic of all the arthropods and is ordinarily their method 

 of providing for increase of size when the old cuticle becomes 

 too tight. They emerge from their transformation with shiny new 

 armor, fully set with new hairs and spines, and often even with new 

 structures not represented in their previous condition. In the spiders, 

 metamorphosis brings with it a rather gradual change from the 

 spiderling to the adult, and is comparable for the most part to the 

 changes undergone by grasshoppers and other lower insects. During 

 each molt the epidermis formed under the old cuticle is capable of 

 considerable increase in size before it becomes hardened. A much 

 greater change occurs at the last molt, for it brings to light the fully 

 developed, sexually mature adult. Only some of the more primitive 

 spiders resort to molting after sexual maturity; they are the females 

 that are long-lived and perhaps require a periodical change of rai- 

 ment for other reasons. Apparently postnuptial molts are not neces- 

 sary for growth, inasmuch as the creatures have reached their 

 maximum and may even decrease in size thereafter. Perhaps they 

 are required in order to provide a new and complete covering of 

 spines and hairs, which are the prime sensory equipment of spiders, 

 and without which they remain at a distinct disadvantage. 



Molting is ordinarily preceded by various symptoms that indi- 

 cate the approach of the ordeal. This is particularly true of the 

 later molts, which are of longer duration and more difficult of suc- 

 cessful completion. For hours, days, or even weeks, the spider re- 

 fuses to feed and becomes more and more lethargic. Certain changes 

 in color have been noted, in some instances a darkening of the legs, 

 in others a lightening or darkening of the whole body, owing no 

 doubt to the changes going on under the old integument. Burrow- 

 ing spiders often spin up the entrance of their burrows or block the 

 opening with a plug of earth. Those that normally live in silken 

 nests or leaf retreats use these for molting quarters. Some of the 

 orb weavers hang exposed in their webs and are thus in an especially 

 vulnerable position. 



The details of molting (Plate X) vary little among groups of 

 spiders, but they are of considerable interest. The large American 



