COURTSHIP AND MATING 69 



SEXUAL DIMORPHISM 



Spiders are to all intents sexless until they arrive at maturity. 

 There is nothing in the general appearance of immature specimens 

 that indicates with certainty femaleness or maleness, and nothing 

 in their early-life activities of digging, hunting, or web spinning that 

 marks either sex. Many people think of immature spiders as being 

 female, and there is good reason for this since they usually more 

 closely approximate the mature female in general appearance. It is 

 probable that ancestral spiders exhibited little sexual dimorphism, 

 and we note that this is true for some (but by no means all) of the 

 more primitive types. Changes in the sexes have occurred both in 

 the female and male, but they have been far greater in the male. 



The female is specialized for a particular function, and, if we 

 presume to evaluate the sexes in finite terms, is a far greater con- 

 tributor to the race than the male. Whereas the male has completed 

 his assignment when he transfers the sperms to the female recepta- 

 cles, the female maintains the eggs in her body until they are ready 

 to be delivered and fertilized, encases them in a silken sac, guards 

 them in various ways, and often is on hand to protect the young 

 spiderlings for a considerable period. Her body has been molded 

 as a receptacle for nurturing a variable number of developing eggs, 

 and it responds to this need by maintaining a greater size than the 

 male. Perhaps in response to her protective role, she is less con- 

 spicuously colored and far less of an extrovert than her male. On 

 the other hand, because of greater size, she is much more powerful; 

 and she is dominated most of the time by predatory instincts inten- 

 sified by her solitary habits. 



Among spiders, the male is a luxury item, developed for the 

 single purpose of transferring the sperm. He offers no protection 

 to the female or the offspring, as do many other animals, and is 

 usually dead before the eggs are laid. He has changed in various 

 ways to become a specialist, and is modified in many ways to play 

 his part more expertly. The force that sends him into the arms of 

 the female ogre is a very strong one, but he has become conditioned 

 to preserve himself by taking flight should he be unwelcome. He 

 has also become conditioned to overpower the female on certain 

 occasions. 



The specialization of the male has proceeded in several direc- 

 tions, and we find a considerable variety of types. In many of the 



