Jumping spiders have excellent vision, with some of the highest vision clarity out of all the invertebrates. You may not already know this, but not all Spiders have eight eyes. However, the Jumping spider does. Four of which are grouped on the face (the two big eyes in the middle, and two smaller Lateral eyes on the side), and four extra eyes on top (two medium-sized eyes toward the back, and two very small eyes in front of them). The two eyes located in mid portion of the front of the face has extremely high clarity but a small field of view, and the remaining six eyes acts more like our peripheral vision. Instead, with a lower resolution but broad field of view.
The Two eyes in the middle front side of the face are long and tubular, which assists in their resolution (longer focal length which in turn helps with adding more magnification) but which means they have a very narrow field of view out of those two eyes. Since those two have such a narrow field of view, the spider needs to point them in different directions in order to be able to view different things. This is partially accomplished by moving the carapace, but the eyes can move too. This is not done by moving the whole eyeball, like we would, since the lenses of the eyes are actually built into the carapace. Instead the whole retina is what moves around, while the lens stays in the same fixed position.
Since the retina is the darkest part of the eye and it moves around, you can sometimes look into the eye of a jumping spider and see it changing color. When it is darkest, you know the spider is looking directly at you because then you are looking down into its retina. It’s kind of creepy in a way, but awesome to see for yourself.
I found this video online which shows you a spider looking around while it is eating a fly.
video credit: zxgirl’s photostream on flickr
Type of Spider: Magnolia Green Jumper, Lyssomanes viridis