Some Observations on the Ecological Variation and Development of the Cruciate Zigzag Camouflage Device of Argiope pulchella (Thor.).

Authors

  • J. E. Marson E.Z.S., F.R.E.S.


Summary.

The cruciate zigzag of Argiope pulchella (Thor.) is not specific, considerable variation in form and size occurring in different habitats. In any type of habitat, however, the type of device used is constant.

The intensity of illumination seems to be the factor determining the size and completeness of the device, the device being more complete and larger with an increase in illumination.

The density of the webbing used in the device and the distinctness of the zigzag formation are apparently controlled by two factors, the intensity of the illumination, and the speed at which the device is constructed. These two are, however, inter-related as an increase in illumination, brings a corresponding increase in the speed at which the device is constructed. Increase in these two factors causes an increase in the density of the webbing used and a decrease in the distinctness of the zigzag formation.

This variation with the intensity of the illumination is reasonable as the effectiveness of the cruciate zigzag as a camouflage device decreases with a decrease in the intensity of the illumination, becoming detrimental when the web is in a dark habitat. It would appear then that Natural Selection has not selected this species because of the cruciate zigzag in its web but because of the spider's ability to modify the device according to the habitat in which it spins its web.

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