title: Upside-down spiders build upside-down orb webs: web asymmetry, spider orientation and running speed in Cyclosa.
abstract: Almost all spiders building vertical orb webs face downwards when sitting on the hubs of their webs, and their webs exhibit an up-down size asymmetry, with the lower part of the capture area being larger than the upper. However, spiders of the genus Cyclosa, which all build vertical orb webs, exhibit inter- and intraspecific variation in orientation. In particular, Cyclosa ginnaga and C. argenteoalba always face upwards, and C. octotuberculata always face downwards, whereas some C. confusa face upwards and others face downwards or even sideways. These spiders provide a unique opportunity to examine why most spiders face downwards and have asymmetrical webs. We found that upward-facing spiders had upside-down webs with larger upper parts, downward-facing spiders had normal webs with larger lower parts and sideways-facing spiders had more symmetrical webs. Downward-facing C. confusa spiders were larger than upward- and sideways-facing individuals. We also found that during prey attacks, downward-facing spiders ran significantly faster downwards than upwards, which was not the case in upward-facing spiders. These results suggest that the spider's orientation at the hub and web asymmetry enhance its foraging efficiency by minimizing the time to reach prey trapped in the web.
authors.affiliation: Faculty of Human Environment, Nagasaki Institute of Applied Science, Nagasaki, Japan. ken@tku.ac.jp
authors.forename: Kensuke
authors.initials: K
authors.lastname: Nakata
authors.forename: Samuel
authors.initials: S
authors.lastname: Zschokke
mesh_terms: D000818:Animals; D008124:Locomotion / Q000502:physiology; D009949:Orientation; D011235:Predatory Behavior; D013112:Spiders / Q000502:physiology*
references.citation: Naturwissenschaften. 2010 Jan;97(1):43-52
references.pmid: 19789847
references.citation: Proc Biol Sci. 2010 Jan 7;277(1678):29-33
references.pmid: 19812081
references.citation: J Evol Biol. 2009 May;22(5):954-63
references.pmid: 19243487
references.citation: Naturwissenschaften. 2007 Oct;94(10):853-7
references.pmid: 17534590
references.citation: Anim Behav. 2000 Mar;59(3):603-611
references.pmid: 10715183
references.citation: Science. 1965 Sep 10;149(3689):1190-7
references.pmid: 17747443