Spiral orientation ofAraneus diadematus orb webs built during vertical rotation

Summary

Standard spider frames were continuously rotated in a vertical klinostat at different speeds, changed each day, in a rising sequence through 0.3, 0.7, 2.3, 4.9, 10, 20, 30, and 60 rpm. They were also rotated at various speeds between 100 and 150 rpm. Speed of rotation did have a marked effect on a number of web parameters. It is concluded that gravity is an important compass reference for orientation during web construction. The effect was greatest at medium speeds, and less pronounced not only at slower but also at higher speeds. The most striking effect was the complete disorientation of the spider during construction of the capture spiral at 5 and 10 rpm. Surprisingly no comparable disorientation was found in the auxiliary spiral. This suggests different orientation mechanisms for the two spirals. The ability to orient the capture spiral at high speeds may be due to the effect of centripetal forces, but it may also be attributed to an evolutionary adaptation to building in windy environments where the spider might experience linear accelerations of severalg.