Monday, October 1, 2012

ORB WEB SPIDERS (Family Araneidae)

Orb webs are the quintessential circular spider webs built between two trees or under the eaves of a roof.  Most of the spiders in this family build some variation on this design.
This is a very diverse family with spiders of all shapes, sizes, colouration, and behaviours.   Females are often almost 1000 times the size of the male.  The orb web is used to trap prey and is often a very beautiful structure.
All members of this family are completely harmless to humans.  Most of them are bound to their webs and will not leave it unless the web is destroyed.
 Above: Caerostris sexcuspidata - BARK SPIDER.  These spiders build a new web every evening after sunset and take it down each morning before sunrise.  During the day they use their superb bark-like camouflage to hide on one of the trees to which their web is attached.
 Above: Cyclosa sp. - GARBAGE LINE SPIDER. These spiders construct a regular orb web but place random debris in a line across the web and hide somewhere amongst it.  Their irregularly shaped abdomen and colouration conceals them perfectly.  Even when the web is disturbed, they do not move, further aiding their camouflage.
 Above: Cyrtophora citricola - TROPICAL TENT WEB SPIDER.  These spiders come in many sizes and colour patterns (the one pictured above is more dull than others).  Their webs are built as large, messy space webs, often amongst long grass next to water or in low Acacia trees.  At the base of the web is a variation of the typical orb-web; a horizontal orb, pulled up in the centre to create a small canopy (as seen in the unfortunately blurry picture below)
 Above: Tropical Tent Web (Cyrtophora sp)
 Above: Gasteracantha falcicornis - KITE SPIDER.  These beautiful, colourful spiders build large, typical orb webs and hang upside down in the centre.  It is thought that their large spikes help to deter predation from birds (although yet unproven).  Despite their somewhat menacing appearance, these beauties are completely harmless to humans.
 Above: Gasteracantha sanguinolenta - KITE SPIDER
 Above: Isoxya tabulata - BOX KITE SPIDER
Above: Neoscona sp - HAIRY FIELD SPIDER.  Similar in size and superficially in appearance to the Bark Spiders (Caerostris spp), these spiders also build large orb webs between trees and under the eaves of roofs to catch nocturnal flying insects.

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