^68 Home Nature-Study Course. 



Facts for the Teacher. — The orb webs are often vertical or nearly so, as tliey 

 are thus much more likely to be in the path of flying insects. The number of 

 radii or " spokes " differ with the different species, and they are usually fastened 

 to a silken frame work and the frame work is fastened by guy lines to surrounding 

 objects. The thread connecting the spokes is in a spiral. The distance between 

 the spirals is usually the same. There is a hub' at the center of the web which is 

 usually surrounded by an open space before the chief spiral begins. The center 

 of the web may be merely an irregular net work surrounded by a short spiral or 

 it may have wide bands of silk laid across it. The radii or spokes, the guy lines, 

 the frame work and the center of the web are all made of inelastic silk, which does 

 not adhere to an object that touches it. The chief spiral line, on the contrary, is 

 very elastic and adheres to any object brought in contact with it. An insect which 

 touches one line and tries to escape becomes entangled in the neighboring lines 

 and is thus held fast until the spider can reach it. If one of these elastic lines 

 be examined with a microscope it is a most beautiful object. There are strung 

 upon it like pearls little drops of sticky fluid which render it not only elastic but 

 adhesive. Some species of orb weavers remain at the middle of the web, while 

 others hide in some little retreat near at hand ; if in the middle the spider always 

 keeps watchful claws upon the radii of the web so that if there is any jarring 

 of the structure by an entrapped insect it is at once apprised of the fact ; if the 

 spider is in a den at one side, it keeps a claw upon a trap line which is stretched 

 tightly from the hub of the web to the den, and thus communicates any vibration 

 of the web to the watcher. When the insect becomes entangled the spider rushes 

 out and envelopes it in a band of silk, which feat is accomplished by turning the 

 insect over and over rapidly, while at the same time spinning a broad band in which 

 to swathe it. It may bite the insect before it begins to swathe it in silk or 

 afterwards. It usually hangs the swathed insect to the web near where it was 

 caught until ready to eat it; then it takes the prey to the center of the web if there 

 is where the spider usually sits, or to its den at one side if it is a den-making species 

 and there sucks its juices and carefully throws away the hard parts. The spider 

 does not become entangled in the web because it runs upon the dry radii and not 

 upon the sticky spiral lines. During the busy season the spider is likely to make a 

 new web every twenty-four hours, but this depends largely upon whether the web 

 has been destroyed by large insects meanwhile. 



Lesson XX. 



HOW AN ORB WEB IS MADE. 



Notes to be Made by the Pupils. — Spiders may be seen making their 

 webs in the earlv morning or in the evening. Find an orb web with a 

 spider in attendance ; break the web without frightening the spider and 

 see it replace it in early evening, or in the morning about daybreak. An 

 orb weaver may be brought into the house on its web, when the web is 

 on a branch, and placed where it will not be disturbed, and thus be 

 watched at leisure. 



