Jumping Spider - Phidippus otiosus
Family Salticidae - Jumping Spiders
Live spiders photographed at eastern North Carolina.
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Jumping Spider - Phidippus otiosus
Salticids, with rare exceptions, do not build webs to snare prey, they only spin small silken retreat webs for moulting or hibernation. When hunting, jumpers always trail a silken strand from their spinnerets. If they are disturbed, they will rapidly descend on this lifeline to the ground and out of sight, or if they miss their jump, they can climb the thread back to their previous perch. These little guys are very adept at hiding, and if they do not want you to see them, you won't.  You can find an extensive article on the family at the Tree of Life Website.

Although a jumping spider can jump more than fifty times its body length, none of its legs has enlarged muscles. The power for jumping comes from a quick contraction of muscles in the front part of the body increasing the blood pressure, which causes the legs to extend rapidly much as the hydraulics in a low-rider car.


The fangs are the red pointed objects, used to inject venom.
Jumping spider's anatomical points of interest:
  • Esophagus passes straight through the 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 marionette puppets
  • 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 the carapace

Note: the function of the posterior medial eyes is unknown [2]
Jumping spiders are easily distinguished from other spiders by their four big eyes on the face and four smaller eyes on top of the head. The diagram above shows how the different focal lengths among the different eyes provide almost 360 degrees of coverage, while still allowing a field of very acute vision directly in front (like most predators). This explains why it is so difficult to sneak up on a jumping spider from behind; almost invariably, they will spot you and turn immediately in your direction.
References
  1. Bugguide.net, Jumping Spider - Phidippus otiosus
  2. Jumping Spider Vision, David Edwin Hill, via Creative Commons Attribution 3.0 Unported
  3. Arthur V. Evans, National Wildlife Federation Field Guide to Insects and Spiders of North America
  4. Clark Kimberling, University of Evansville, "Thomas Say, Father of American Entomology"
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