When I was down at TTPBRS on Thursday, it was a pretty quiet day. Not too many birds around, so I spent some time examining the walls of one of the buildings for bugs or other interesting things. One of the creatures I came across was this jumping spider. Jumping spiders are tiny, less than a centimetre long, and fairly stocky. This particular one is a Zebra Spider (Salticus scenicus), so called for the striping on its abdomen. It’s a species with a holarctic distribution, found nearly throughout the northern hemisphere. There are more than 5000 species in this family of spiders, which represents nearly 13% of all spider species, the largest taxonomic family of the arachnids.
Jumping spiders have excellent vision, aided by two giant eyes placed on the front of their head, which gives them strong binocular vision, but in a narrow field of view. They have eight eyes total; two others are also located on the front of the head, but the other four are on their back. These remaining six provide the spider’s peripheral vision. They are also amazing jumpers (hence the name of the group). They don’t have the large leg muscles of some jumping insects (such as grasshoppers). Instead, their spring power comes from a hydraulic-like system that uses their interior body fluid (insects and spiders have their “blood” loose in their body cavity, rather than contained in a vascular system) to rapidly extend their legs.
Some jumping spider species can grow quite large; one African species can reach 14 inches in length. These massive spiders have been recorded to jump as far as 7 feet in a single leap. In the larger spiders, where you can clearly see their eyes, you can watch which way they’re looking. This is because the retina of the spider’s eye sits loose at the centre of the back of the “eyeball”, and the spider moves it around, rather than moving the eye itslef, in order to see. This causes the visible colour of the eye to change, depending on where the retina is. When the eye is blackest, the spider is looking right at you.
All spiders are predators, there are no herbivorous spiders. Zebra spiders feed on other insects and spiders that are their own size or smaller. As I stood there and watched this individual, snapping photos, I noticed a small brown spider crawling up the wall towards the Zebra, apparently oblivious.
The Zebra honed in on it right away. It patiently waited for the brown spider to pass it, actually moving out of its way, to one side, to allow it to do so.
Then, once the brown spider’s back was turned, the Zebra lined itself up, gathered its legs under itself…
The brown spider made it out alive by rapidly letting go of the wall and dropping down on a thread. A happy ending for the brown spider, not so happy for the Zebra.