The Atavism

Friday, July 13, 2007

Arachnophilia

I like spiders. I mean I really like spiders. So, even though my recent field trip to the Cook Islands was all about the landsnails, and I collected hundreds of them, I wasn't going to miss the opportunity to explore a whole new spider fauna. It would actually have been impossible to avoid sipders in the cooks, blazing a trail through the bush means you find yourself reflexively expelling air and scrapping an unseen web of you every couple of minutes. The web spinning spiders behind these snares are only the tip of the arachnid iceberg though, so today I’m going share some pictures of a spider that takes a completely different approach to getting fed.
A. whitneei, side on
That’s Athamas whitmeei, a widespread pacific jumping spider. Quite often my search for arboreal snails on the leaves of shrubs on Rarotonga’s mountains would also turn up these guys with their wonderful orange spots (which are worn only by the males). The one in the photo was actually stalking around our motel unit while I was taking photos of snails so I guess they’re quite happy to adapt to different environments.
Look into my eyes…
Unlike their passive, web-spinning cousins jumping spiders need to go out and hunt their food. As a result they have very good vision. The two large, forward-looking eyes can resolve and image onto their retina which appears to be have four different classes of ‘cones’ (one more than our red, green and blue tuned cells) which may allow them to see a much greater range of colours than ourselves. Even sharp-eyed hunters can fall prey to other hunters. For mammals and birds choosing where to place your eyes is something of a trade off. Forward facing eyes like Athamas’ help you zero in on your target but limit your ability to see around you. Hence sheep with eyes on the side of their head and wolves with forward looking ones. Athamas as no such trade-off to make, having eight eyes in your body plan leaves a couple spare to point backwards!
Look into my eyes…
Posted by David Winter 2:23 PM

1 Comments:

What a neat looking spider. I've always thought that jumping spiders were more interesting than the orb webs - active hunting make them seem so much more alive. Not that spider webs aren't cool.

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