Bold Jumping Spider - Phidippus audax
Also commonly called daring jumping spider. Spider Family: Salticidae
Live jumping spiders photographed in the wild at Winfield, Illinois, and San Antonio, Texas, USA.
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Daring Jumping Spider - Phidippus audax
Jumping spiders have acute stereoscopic vision, thanks to their large, forward-facing eyes. But rather than move the eye itself, as most animals do, the jumping spider moves the retina behind the eye. The iridescent green chelicerae are diagnostic of the genus Phidippus in the jumping spider family, Salticidae.
Daring Jumping SpiderDaring Jumping SpiderDaring Jumping Spider
Jumping spiders do not build spider webs for trapping prey - they use them for hiding and laying eggs only. Prey is stalked and killed much like a cat stalks a bird. A spider silk lifeline is always at the ready; if threatened, these guys rapidly lower themselves into the underbrush. They also use the line to climb back into position should a jump go awry and they miss their target.
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Daring Jumping Spider - Phidippus audax
Come for the sometimes frenetic activity, strange courtship dances, voracious carnivorous habit and stay for the eyes. Oh, those peepers.

Jumping spiders have excellent vision, among the highest acuity in invertebrates. The eight eyes are grouped four on the face (the two big anterior median eyes in the middle, and two smaller anterior lateral eyes to the side), and four on top of the carapace. The two large, forward-facing eyes (AME) are tubular behind the lens, with a well-developed musculature, unique to salticids, that supports and moves the retina - the opposite arrangement of our own eyes. [1]

Spider musculature is also different from ours: in the spider, muscles operate from the inside to move external skeletal elements; our own skeletal muscles surround the elements they operate. But even these glaring differences are nothing compared to the jumping spider's brain and digestive system - their esophagus passes right through the brain, and one branch of the gut (analogous to our intestines) actually overlies the eyes and brain! [3]
Daring Jumping Spider - Phidippus audax
Jumping spider's anatomical points of interest:
  • Esophagus passes straight through the spider's brain
  • Portion of gut overlies the eyes and brain inside carapace
  • Heart extends from abdomen into cephalothorax
  • Leg muscles attached inside the carapace operate legs like a marionette puppet
  • Jumping spider's brain volume to body size proportionate to human, but visual processing region is larger
  • Salticids move retinas inside the eyes to look in different directions, as the lenses are fixed in carapace [3]
References
  1. Bugguide.net, Jumping Spider - Phidippus audax
  2. Maddison, Wayne. 1995. Salticidae. Jumping Spiders. Version 01 January 1995

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