Some orb weavers do not wait upon the hub but have a retreat near one edge of the net, in which they hang back downwards. While resting in these retreats they keep hold of some of the lines leading from the net, 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 adheres 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 elasticity of the sticky line, most insects could readily tear themselves away before the spider had time to reach them. In running over its net the spider steps upon the radii, carefully avoiding the sticky line; otherwise it would destroy its own net. The rapidity with which a spider can cross its net without touching the sticky line is remarkable. In making its web an orb weaver first spins a number of lines extending 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, as the branches of two separate bushes. How did the spider cross the gulf? It has no wings. [Illustration: _Fig. 93. Nearly completed orb-web._] The bridge building can be easily seen on a warm summer evening, the time at which the spiders are most active repairing their old nets and building new ones. The spider lifts the hind end of its body and spins forth a thread; this is carried off by the wind, until, finally striking some object, it becomes fast to it. The spider then pulls in the slack line, like a sailor, and when the line is taut fastens it to the object on which it is standing, and the bridge is formed. After making the outward framework, the radiating lines are formed. A line is stretched across the space so as to pass through the point which is to be the center of the orb. In doing this the spider may start on one side, and be forced to walk in a very roundabout way on the outer framework to the opposite side. It carefully holds the new line up behind it as it goes along, so that it shall not become entangled with the lines on which it walks; one or both hind feet serve as hands in these spinning operations; for, as the spider has eight feet, it can spare one or two for other purposes than locomotion. When the desired point is reached the slack is pulled in and the line fastened. The spider then goes to the point where the center of the orb is to be, and, fastening another line, it walks back to the outer framework, and attaches this line an inch or two from the first. In this way all of the radiating lines are drawn. The next step is to stay these radii by a spiral line, which is begun near the center, and attached to each radius as it crosses it. The turns of this spiral are as far apart as the spider can conveniently reach.