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Marcus Ranum says
It’s interesting to try to infer predator/prey relationships and practices from the arrangement of the eyes.
Where are the sparassids, dammit?!
They are all predators, do you mean predation method? Pretty much all of them involve sitting in a web of some sort and waiting for prey, but notice the salticids, with the giant central pair of eyes dwarfing the rest. That binocular vision is good enough for depth perception, which is particularly suited to say… jumping.
Those are eyes?
And here I was thinking that they were footprints.
Since you are on holiday you might want to take a little collecting field trip to Lake Vistonida.
Marcus Ranum says
They are all predators, do you mean predation method? Pretty much all of them involve sitting in a web of some sort and waiting for prey, but notice the salticids, with the giant central pair of eyes dwarfing the rest.
Yes “predation method” was what I was looking for. Presumably some of the spiders are keeping one eye on their prey and another eye out for birds and I don’t know what all else with the other 6. So it’s a predator/prey balance thing.
I was thinking a spider that generally hunts along the ground might have eyes in different places from one that sits in a web and looks for things that fly around.
I like your point about the jumping spiders.
PZ Myers says
Sparassid, for those who don’t know them.
I got my start in grad school studying Salticid sensory physiology. Another cool thing about them is that their main eyes are not orbs at all — they’re long cylinders, more like a telescope. Watch them some time, they make these herky-jerky movements of their whole prosoma as they swivel their whole head around to track objects.
The lycosids (wolf spiders) also show a similar arrangement, with a pair of prominent eyes they use in binocular vision for hunting.
A lot of spiders don’t rely much on vision, using tactile senses to detect prey in their webs, so the arrangement might be less about functional optimization than chance organization of generic threat detectors.
By the way, spiders generally have 8 eyes, but they seem to arise developmentally from a single pair of primordia, or eye fields, that subsequently divide and migrate to their final destination.
yes the eyes are very different. spider webs also very a lot so I would guess that each type of web functions in a different way as well so that would suggest different details with predation methods as well as prey are expressed in the spider’s eyes and their whole body shape as well as the web.
Holms @2: You want “giant central pair of eyes dwarfing the rest”? I give you giant central pair of eyes dwarfing the rest! I wonder what the orange/red color patch containing the other eyes is all about?
I quite like the aesthetics of the Ctenizidae. It’s almost like the eye pattern also doubles as an icon for spiders. On the other hand, the Agelenidae 2 gives me a warm nostalgia because it reminds me of the aliens in Space Invaders.
3 sets of duplex eyes. In this area it is the consistent positive identification method for my nemesis, the brown recluse.
I wonder developmentally what became of the other pair? Probably traded them to the god of evolution for its venom and hard claw on the end of its legs to walk over poison dust.
I am amazed that they can use 8 eyes for vision. I can sometimes get confused just with my two eyes and optical illusions. Are they all functioning eyes or are the non-central ones more like threat detectors to signal a need to focus the central eyes on something to identify it? I am an arachnophobe, but the whole idea of spider vision with multiple sets of eyes is quite fascinating to me, as are other aspects of spiders. I just can’t watch them, or think of them in certain ways.
They actually can’t, kinda. Research has shown that most of their eyes are very poor, especially for the web spinners. Only the central pair of eyes on the roving, hunting types of spiders have well developed vision, the rest are just for peripheral warnings of motion.
Akira MacKenzie says
Arachnids aside, “In Your Eyes” is my favorite Peter Gabriel song.