Thursday, 23 August 2007
Gasteracantha fornicata is an Art Noveau brooch of a spider, a blend of curves and spikes enamelled in black, red and yellow. The combination of colours makes it stand out from its background. Advertising this way might not seem like a good strategy for a predator. Hello, here I am in the middle of this almost invisible orb web is not the best way to trap unwary insects.
Or is it?
By manipulating the colour of G. fornicata from the Daintree region of Far North Queensland, Mark Hauber found that brightly-coloured individuals had greater success with prey than soberly-dressed ones. Perhaps there's something about the contrasting colours that entices the more reserved insects to their doom?
Hauber also noticed that the spiders sit on the undersides of their webs, so their darker derrieres are viewed against vegetation and their gaudy tops against the light. He suggested that this behaviour might be part of the trap — maximising the chances of intercepting insects as they fly up from nearby plants.
I photographed this individual at the Flecker Botanical Gardens in Cairns. This is how the colour patterns appear to us. I'd love to see how they'd appear to insects.
Hauber, ME. (2002) Conspicuous colouration attracts prey to a stationary predator. Ecological Entomology 27(6): 686–691. (Abstract available at Blackwell-Synergy)
* This was the first spider species described from Australia. Johann Christian Fabricius named it in 1775 from material collected by Joseph Banks from the Endeavour River region. I haven't seen the original description, so I'm not sure why it received that curious specific epithet. Probably best not to inquire.