THE AERIAL WEB SPINNERS 159 



almost invariably fix guy lines with sticky globules to hold their vic- 

 tims. The sheet web weavers use both maze and sheets of various 

 forms. The sticky spirals of the orb weavers hold fast an array of 

 jumping and flying insects. Along with the webs, there have de- 

 veloped most interesting techniques for overpowering and enmesh- 

 ing the victims; and the basic factor upon which these techniques 

 depend is the spider's ability to move upon the web. 



The successful venture in silken lines is made possible by the 

 unpaired median claws, which lie between the much longer outer 

 pair and near their base. The median claw in aerial spiders is 

 shaped like a hook, and is provided with a few small teeth. Associ- 

 ated with it are various modified hairs, which, often curved and 

 toothed, are called "spurious" or "accessory" claws. The median 

 claws are used almost exclusively for clinging to the lines of dry 

 silk. They are displaced slightly to the sides, those of the first and 

 second tarsi toward the anterior and those of the third and fourth 

 tarsi toward the posterior outer claw. This facilitates grasping of 

 the threads, which fit into the hook of the claw without requiring 

 a turning of the tarsus. When walking in the web, the spider draws 

 the tarsi across the threads to catch the median claw, which grasps 

 the line at an acute angle and twists it to make the grip firmer. 

 The spurious claws orient the threads so that they can be hooked 

 by the median claw, then act to clear the thread from the notch 

 by uncoupling and hurling it out. With this effective device, the 

 aerial spider moves through deep mazes or across vertical meshes 

 with ease and precision. 



Before passing on to brief sketches of the major groups of aerial 

 spiders, some generalizations can be made that indicate the pro- 

 found differences between them and the hunting spiders (discussed 

 in the following chapter). Both are derived from the same prim- 

 itive stocks, and on their separate roads both have become amaz- 

 ingly specialized. The success of each line is attested by the vast 

 number of species found living side by side, and by the develop- 

 ment in each series of a wide and amazing variety of types. In 

 terms of degree of change from prototypes, the sedentary spiders 

 have outdistanced the hunters. The spinners live in holes under 

 the ground, they live near or on the surface, they live in surface 

 vegetation, shrubs, and high up in trees. They have invaded aerial 

 space with their threads, and claim it as their own by mere place- 

 ment of their three-dimensional webs. As for the vagrants, they 

 are dominant on the soil and in the various strata of plants. They 



