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Animalia >Arthropoda >Arachnida >Araneomorphae >Araneidae >Cyclosa >

In vertical orb-webs of most spider species, lower radius is larger than upper radius (up-down asymmetry). This is considered to reflect spider's optimal investment of web thread between upper and lower half of web, since spiders can move and reach trapped prey faster downward than upward.

This movie is about an orb-web spider <i>Cyclosa octotuberculata</i>'s assaulting behaviour for upper and lower directions. The spider runs faster downward, perhaps due to gravity. Moreover, the spider takes longer time to locate prey in upper part of web (The spider pulls web thread to locate prey), and it firstly runs to the direction slightly leftward from the prey and costs extra time.

(Data No.momo051103co01b)

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