Sunday, April 07, 2013

Eyes in the back of her head

This zebra jumper was waiting for us on the wall by the door the other day.

An active little critter, constantly turning to get a better view of the camera.

And around the corner, on an Oregon grape, I found this red-brown jumping spider.

A smaller spider, even more alert, jumping from leaf to leaf to bud, checking me out.

I noticed, browsing through BugGuide once again, how many people described their jumpers as "cute". It was the word I had used, to myself, about this second spider. Smaller than the zebras I see more often, and very interested in my camera, staring it down. I think it's the big "headlight" eyes, too big for the spider's tiny face, that we find appealing.

But I was trying to get a look at the other six eyes. The jumping spider has the two big eyes at center front, then two smaller forward-facing eyes beside them.

Typical arrangement of Jumping spider eyes. From BugGuide.

The other four eyes are on the side and top of the cephalothorax, the combination head/chest of a spider. These eyes are much smaller, and often very hard to see. On the zebra at the top, I can pick out three of them; on the brownish spider, only one gleaming red eye is visible.

These eyes don't have the acute vision that the big eyes do, but they do pick out motion, which is why you can't sneak up on a jumper from behind; she'll immediately turn to stare you in the face.

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