GEOMETRICAL SPIDERS 85 



insects. In a dry season there is a marked diminution 

 in the dragon-flies and the robber-flies that hunt 

 insects on the wing. Similarly will the insectivorous 

 birds be reduced in numbers, and each species will 

 affect each other species in the complex web of life. 



The mode of construction of the snare is similar in 

 these two species of Epeira ; yet it is obvious that 

 Araneus has a decided preference for suspending its 

 web in the vertical and Tetragnatha in the horizontal 

 plane. This wonderful architecture has often been 

 described, yet I here take the liberty of again display- 

 ing the method of work in order that the subsequent 

 experiments that I made on the snare may be found 

 the more intelligible. 



I isolate an Araneus on the tip of a blade of grass 

 standing in a shallow pool. The spider is cut adrift 

 from land ; it is marooned and cannot escape. I sit 

 down to see how it will act. The hour of work is at 

 hand, so the spider soon sets about the construction of 

 a snare. A series of successive stages now follows, 

 each stage a definite step in the architecture, a 

 preparation for the succeeding stage. The first 

 essential are some foundation-lines to serve as a 

 framework for the snare. The spider begins. It 

 climbs to the tip of the blade of grass ; it elevates its 

 abdomen and from its spinnerets emits a silken 

 filament to the wind. The light filament is wafted to 

 the shore, becomes entangled in another blade of 

 grass, and the first foundation-line is in place. Back- 

 wards and forwards runs the spider along its line, 

 adding each time a new filament, doubling, trebling, 

 quadrupling the line until it is strong and sound. 

 The first foundation-line is secure, For the second 



