It's time that I introduce you to the guests of honor of my posts, the jumping spiders, known to biologists by the name "Salticidae". Imagine a miniature cat, 5 millimeters long, spotting prey with keen eyesight, walking carefully toward the prey, then crouching down, inching forward stealthily, tensing its legs, then pouncing with deadly accuracy. That pretty much describes a jumping spider. They hunt like cats, using their acute vision and jumping ability.
Like most spiders, jumping spiders have 8 eyes. Six of these look all around, like our peripheral vision. The two other eyes, in the front middle, are like our fovea, our central vision: narrow field of view, but high resolution. These are the great big eyes in the middle of their faces. You can see photos of these special eyes and how they move in my account of a transparent jumping spider from a recent expedition to Ecuador. What's remarkable is that they can achieve such an acute visual system in such a small package.
As for their jumping, you might wonder: to jump, why don't they have big muscular back legs like a kangaroo or a grasshopper? The answer is surprising. Jumping spiders don't use muscles in their legs to jump. Muscles elsewhere in their bodies contract to raise the blood pressure suddenly, which causes the legs to inflate abruptly and snap straight. A hydraulic jumping mechanism.
Jumping spiders live all around the world except the extreme polar regions. They live in forests, deserts, prairies, and in cities. There's a good chance there is one within 100 meters of you right now.
Previously in this series:
Text and images © W. Maddison, under a Creative Commons Attribution 3.0 license (CC-BY)