INSECTS AND THEIR NEAR RELATIVES 



15 



about one-half an inch in length. This spider is common all over the 

 southern states and occurs as far north as Pennsylvania and Ohio, at least. 



Family Argiopid^e 

 The Orb Weavers 



Few if any of the structures built by lower animals are more wonder- 

 ful than the webs of orb-weaving spiders, but these beautiful objects are 

 so common that they are often considered hardly worthy of notice. If 

 they occurred only in some remote corner of the earth, every one would 

 read of them with interest. 



The webs of the different species of orb weavers differ in the details of 

 their structure, but the general plan is quite similar. There is first a 

 framework of supporting lines. The outer part of this framework is 

 irregular, depending upon the position 

 of the objects to which the web is 

 attached; but the more central part 

 is very regular, and consists of a num- 

 ber of lines radiating from the center 

 of the web (Fig. 31). All of these sup- 

 porting lines are dry and inelastic. 

 But there is spun upon the radiating 

 lines in a very regular manner a thread 

 which is sticky and elastic (Fig. 17, 

 p. 8). Usually this sticky thread is 

 fastened to the radiating lines so as to 

 form a spiral, but a few species make 

 webs in which this thread is looped 

 back and forth. 



Many of the orb weavers 

 strengthen their webs by spinning a 

 zigzag ribbon across the center. This 

 ribbon is made by spreading the 

 spinnerets apart so that the minute 

 threads from the spinning-tubes do not unite to make a single thread, as 

 is usually the case. 



Some of the orb weavers live in their webs hanging head downward, 

 usually near the center of the web; others have a retreat near one edge 

 of the web, in which they wait for their prey. While resting in these 

 retreats they keep hold of some of the lines leading from the web, so 

 that they can instantly detect any jar caused by an entrapped insect. 



When an insect in its flight touches one of the turns of the sticky 

 line, the line sticks to it; but it stretches so as to allow the insect to 

 become entangled in other turns of the line. If it were not for this elas- 

 ticity of the sticky line, most insects could readily tear themselves away 

 before the spider had time to reach them. 



In making its web an orb weaver first spins a number of lines extend- 

 ing irregularly in various directions about the place where its orb is to be. 

 This is the outer supporting framework. Often the first line spun is a 

 bridge between two quite distant points. This is done as described on 

 p. 9. Having a bridge across the place where the web is to be, it is an 



Fig. 31. — Partially completed web of Argiope. 



