Natures wonders: Jumping Spider eyes (Introduction)

by David Turell , Saturday, April 15, 2017, 18:43 (2567 days ago) @ David Turell

They've got eight for a very full range of vision:

https://aeon.co/essays/an-enigmatic-spider-and-the-fragile-threads-of-human-memory?utm_...

"P. mystaceus, which lives in North America, is a jumping spider. It is one of about 5,000 species in a highly successful family of arachnids (eight-legged, air-breathing, venom-fanged arthropods) that thrive almost everywhere except Greenland and Antarctica.

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"Some species have better visual acuity than cats, which are more than 100 times their size, and though each of their pairs of anterior eyes has a limited field of view, the full complement of eight allows them to scan large sections of the world around them. (Like most spiders, they also have acute hearing, mediated by tiny hairs on their legs which are sensitive to the smallest vibrations.) They are much more powerful jumpers than cats, able to pounce up 50 times their body length and land with precision. And they have a safety rope: a silk thread tethered to the launch point in case they misjudge their leap and fall short. A jumping spider is a voracious panopticon, bungee-jumper and traceur in one.

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"...the beauty of some jumping spiders is more apparent in their brains than their bodies. Just as we create patterns of the world, searching it for faces and symbols, they are mapping out their own lives in surprising detail. The drabbest genus contains some of the cleverest species known. Among them is Portia labiata, a jumping spider of South and East Asia that lives solely on the flesh of other spiders. P. labiata varies and adapts its behaviour according to the characteristics of the species it is hunting: using trial and error it observes and then mimics rhythms tapped out by species it has not encountered before in order to deceive them, and plots devious lines of attack if a full frontal assault looks too risky. The spider may spend an hour or more scanning the tangles of vegetation and gaps between itself and its intended victim, calculating the best route for a surprise attack. Scientists believe the reason labiata takes so long to do this is because, for all its excellent vision, it has very limited ability to take in and process information. So it systematically scans small sections of the surroundings with its anterior eyes, gradually building up enough information in its memory to build a mental map which it can then use. It’s a little like trying to download a large and fine-grained picture over a very slow internet connection. Once the map is complete, however, Portia will usually execute without fail, rapidly retracing its course if it finds it has started down a blind alley, choosing the correct option and finally swooping on its prey like a special forces ninja."

Comment: The spider obviously uses its brain to plan its attack. It must need all its eyes for the 3-D analysis of how to pounce. Each attack will be different, as circumstances will vary in each chance encounter. So the spider slowly plans each. the issue is not that the brain works efficiently, it is how did this spider reach its current form, bit by bit or all at once? All at once by design seems most logical. It could not live by jumping (pouncing like a cat)without its optical system intact for full 3-D planning.