Jumping Spider - Habronattus decorus
Family Salticidae - Jumping Spiders

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Live adult jumping spiders photographed in the wild at Edina, Minnesota.
Jumping Spider - Habronattus decorus
Genus Habronattus is a large diverse genus of medium-sized salticids, primarily ground-dwellers and with highly ornamented males that perform complex courtship displays. Approximately 100 species are known, most from North America, the remainder in the neotropics.  Most are ground-dwelling on open ground with sparse vegetation, especially on rocks, dry leaf litter and sand. The arid southwest has many species, but Florida also has many species, and others are known above the Arctic circle and east to maritime Canada.

Identification: The elbowed tegular apophysis ("conductor") of the palp is distinctive. The third leg is much longer than the fourth, distinguishing these from other superficially similar genera such as Sitticus. The epigynum has a triangular or tubular guide. [3]
Jumping Spider - Habronattus decorus
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

Jumping Spider - Habronattus decorus

Jumping Spider - Habronattus decorus

Jumping Spider - Habronattus decorus

Jumping Spider - Habronattus decorus

Jumping spiders have excellent vision, among the highest acuity in any invertebrate. The eight eyes are grouped four on the face 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]


Note: the function of the posterior medial eyes is unknown [4]
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 sits on top of the eyes and brain. [1]
References
  1. Bugguide.net, Jumping Spider - Habronattus decorus
  2. Arthur V. Evans, National Wildlife Federation Field Guide to Insects and Spiders & Related Species of North America (Sterling, 2007).
  3. Maddison, Wayne. 1995. Salticidae. Jumping Spiders. Version 01 January 1995
  4. Jumping Spider Vision David Edwin Hill, licensed under the Creative Commons 3.0 Unported
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Class Arachnida / Order Araneae: Spiders are the largest group of arachnids.  They are easily recognized by their eight legs, and there are few creatures great or small that elicit such irrational fear in mankind. The vast majority of spiders are completely harmless and offer beneficial services, chief of which is keeping the burgeoning insect population in check. I am continually amazed at the resourcefulness of these supremely successful predators.
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