70 AMERICAN SPIDERS 



hunting spiders the sexes are quite similar in size and seemingly 

 nearly equal in strength. But even with these there are noticeable 

 differences. The abdomen of the male is slimmer, and frequently 

 clothed with somewhat different hairs and patches of setae. The 

 color pattern of the males is almost always somewhat brighter, even 

 though the species be classified as drab. In these spiders of nearly 

 equal size (the Lycosidae, Oxyopidae, Gnaphosidae, Clubionidae, 

 and others), the outstanding feature of the male is his somewhat 

 longer legs, which give him a greater range of sensory perception 

 and are thus important in evading and overpowering the female. 

 This disparity in leg length is presumably maintained because of 

 and correlative to the quite different modes of life of the sexes, and 

 the dedication of the whole adult life of the male to sex. Among 

 the spiders that have quite similar sexes except for the longer legs 

 of the males are the trap-door spiders. We can interpret in various 

 ways the difference in leg length. In addition to the advantages 

 enjoyed during the courtship and mating, it may mean that the male 

 is better fitted to wander about in search of the female. On the 

 other hand, the longer legs may represent the more generalized 

 condition, and the shortening of the legs of the female a response 

 to the burrowing habit. 



Sexual dimorphism manifests itself in pronounced difference in 

 size in many of the higher web spiders. Among the orb weavers 

 exist all intergrades between a near equality of the sexes and a reduc- 

 tion of the male size to an infinitesimal portion of the female bulk. 

 The large humped orb weavers have males that are nearly equal to 

 their females, but in other members of the same genus Aranea the 

 male may be one fourth her size. In Argiope (Plate XVIII), Cy- 

 closa, and many other genera, the male is much smaller than the 

 female, in the first genus being about one fourth as long. The dis- 

 parity is far greater in Nephila, where the female of the American 

 species weighs more than one hundred times as much as the male, 

 and in some exotic species is said to be over one thousand times 

 larger than the male. The male is also a pygmy among such spiders 

 as Mastophora (Plate III), Gasteracantha, and Micrathena. A re- 

 markable sexual dimorphism exists also among the comb-footed 

 aerial spiders, the Theridiidae, and the vagrant crab spiders of the 

 family Thomisidae. 



The smaller size of the male gives it certain advantages during 

 courtship and mating, and perhaps is used to counterbalance the 

 physical superiority of the female. In Mastophora and Nephila it 



