|Jumping Spider - Platycryptus undatus|
Family Salticidae - Jumping Spiders. Also commonly called daring jumping spider.
Live jumping spiders photographed at Ogle County, Illinois.
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Jumping spider vision allows complex communications such as the elaborate courtship dances that males perform. Salticids are perhaps as old and diverse as mammals, though not many humans know their world. Many salticids are colorful, they take on a variety of body forms, and some have disguises, looking like ants and other organisms. The bright colors and elaborate forms of some jumping spider species are involved in courtship.
Jumping spiders are small to medium in size, stout-bodied and short-legged, with a distinctive eye pattern. The body is rather hairy (pubescent) and frequently brightly colored or iridescent. Some species are antlike in appearance. The jumping spiders forage for their prey in the daytime. They approach prey slowly and, when a short distance away, make a sudden leap onto the unfortunate animal. They are good jumpers and can leap many times their own body length. 
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. 
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! 
|Jumping spider's anatomical points of interest:|
Male jumping spiders have an unusual method of sexual intercourse: they use their palpi, the little "feelers" beside the face - in females, these palpi are simple and leg-like. Both males and females use them like little hands, to manipulate food and to clean their faces. But adult male palpi are larger and much more complex (that's one way to tell a male spider: adult and sub adult males have the palpi swollen like boxing gloves).
When the male is ready to mate, he spins a small web and deposits a drop of sperm on it from the underside of his abdomen. He then places the tip of the palp into the sperm, and draws the sperm through the palp's opening into the sperm duct, where it is stored. He then goes cruising for chicks. If he finds one, he performs a courtship dance for her, during which she assesses his fitness. If she accepts him, he places his palp against an opening on the underside of her abdomen (her epigynum), and guides it into place by putting a thumb-like projection, the tibial apophysis, into a groove in her epigynum. The palpus then expands, locks in place, and injects the sperm. 
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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