Monday, June 25, 2012

Jumping spiders

This is a woodland jumping spider, Thiodina sylvana.  They are members of the family Salticidae, which contains all of the jumping spiders and is the largest spider family.  Like all spiders, these little guy have eight eyes, but their eye arrangement is slightly different then other spiders.  Their eyes are in a single row around their head, with two large eyes right in the middle.  Those eyes have a movable retina, and are able to focus very well, but have a very narrow field of view.  They also posses 4 different photoreceptive layers which each focus at a slightly different plane.  By comparing the focus of the different colors against the perfectly-focused deep layer, they can get a sense of how far an object is away from them [1].

They use this knowledge to stalk their prey and jump out at them.  As their name implies they are superb jumpers and can jump up to 30 times their body length.  That would be like a human jumping 180 feet (or 54 meters)!  They often attach a dragline before jumping, just in case they miscalculate.

This spider is preparing to jump up to the leaf above it.
They also have a fairly complex courtship, with males displaying different colors on their body, including UV patches, and producing sounds to entice the female to mate with them [2.3].  Several sources seem to imply that there is a color-based sexual dimorphism in this species, with the females being lighter in color then the males.

Male woodland jumping spider?
Since these pictures were taken on the same plant, and the lighter markings were the same, I'm inclined to agree that this was a male female pairing.  Enjoy some video of these guys in acton... and in the second clip, look for the dragline as the male jumps down stalks his prey.

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