Pale crab spider

Posted: Wednesday 23 April 2014
by Richard Jones

Here’s one for the arachnophobes. Not because I want to scare anyone, or offend, but in the hope of some progress towards reconciliation.


Here’s one for the arachnophobes. Not because I want to scare anyone, or offend, but in the hope of some progress towards reconciliation. The pale crab spider, misumena vatia, is about as far from dark, menacing, long-legged creepy-crawly as you can get; in fact, it’s really just a flower with legs.
 
That’s the point, of course, because miseuma is a sit-and-wait predator, and its pale hues particularly suit it when perched on a similarly pale-coloured flower. The usual colour range is anywhere from pure white to pistachio ice-cream green, so the bright yellow one in the image above is right in the middle.
 
On a dandelion it would have been all but invisible, as is the white form on an ox-eye daisy; however, like many camouflaged animals, it isn't just the colour-match that hides it, but the colour juxtaposition which confuses the eye of prey or predator. When I saw it, sitting brazenly on a large shining ivy leaf in the slanting rays of the afternoon sun, I did a double take. It took me a squinting moment to recognise what it was, even though this is a widespread and familiar creature.
 
Against the glossy green leaf, the spider’s seemingly bright lemon bon-bon colour made it look very un-spiderlike; most spiders are dark, after all. Then there was the asymmetric leg pose, which cleverly disguises the eager waiting claws ready to grasp a hapless fly up to the deadly jaws. My first, not quite fully formed subconscious thought was of a flower bud, or fallen calyx, and it was only as I shifted position for a closer look that recognition dawned.
 
Apart from being beautiful, misumena is fascinating because it can change its body colour to better match the exact colour of the flower upon which it finds itself. Granted, it takes a few days to complete this chameleon feat, but that’s pretty damn impressive. Intuitively, this suggests the spiders are deliberately adjusting their body colour to better hide amongst the petals; but insects see flower colours differently from us. There is experimental evidence that colour-matching actually makes no difference to prey-catching success rates (the experimenters had fun swapping spiders between different flowers to study this). So exact shade may be less important than simply being an unlikely pallid blob in the herbage, just as in the case of my leaf-perching specimen.

 





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oldchippy 24/04/2014 at 11:49

Hi Richard I had one last year on the flat flower head of a dogwood,The flower had pick a tinge on white and the spider matched the colours at first I didn't see it as I was looking at a butterfly.