ORB-WEBS 345 



As has been said, the spider can throw into play a varying 

 number of spinning tnbes at will, and in point of fact those 

 used in laying down these foundation-lines are either two or 

 four in number. The spider, however, often finds it necessary to 

 strengthen such a line by going over it afresh. 



Every one must have noticed that orb-webs frequently bridge 

 over gulfs that are clearly quite impassable to the spider in the 

 ordinary way. They often span streams — and Epeirid spiders 

 cannot swim — or they are stretched between objects unattainable 

 from each other on foot except by a very long and roundabout 

 journey. When this is the case, the animal has had recourse to 

 the aid of the wind. A spider of this family placed on a stick 

 standing upright in a vessel of water is helpless to escape if the 

 experiment Ije tried in a room free from draughts. With air- 

 currents to aid it, silken streamers will at length find their way 

 across the water and become accidentally entangled in some 

 neighbouring object. When this has happened, the spider hauls 

 the new line taut, and tests its strength by gently pulling at it, 

 and if the result is satisfactory, it proceeds to walk across, hand- 

 over-hand, in an inverted position, carrying with it a second line 

 to strengthen the first. This is exactly what happens in nature 

 when a snare is constructed across chasms otherwise impassable, 

 and it may be imagined that the spider regards as very valuable 

 landed property the foundation lines of such a web, for, if de- 

 stroyed, the direction or absence of the wind might prevent their 

 renewal for days. They are accordingly made strong by repeated 

 journeys, and are used as the framework of successive snares, till 

 accident at length destroys them. 



A single line which finds anchorage in this way is sufticient 

 for the purposes of the spider. It has only to cross over to the 

 new object, attach a thread to some other point of it, and carry 

 it back across the bridge to fix it at a convenient spot on the 

 surface which formed the base of its operations. Between two 

 such In'idge-lines the circular snare is constructed in a manner to 

 be presently described. Sometimes the tentative threads emitted 

 by the spider travel far before finding attachment. In the case 

 of the English Ei^eira diademata the writer has measured bridge- 

 lines of eleven feet in length ; and with the great Orb-weavers of 

 tropical countries they frequently span streams several yards in 

 width. 



