Bug Day (12): Jumping Spider

Red-backed Jumping Spider (Phidippus johnsoni)

The Red-backed Jumping Spider (Phidippus johnsoni) weaves a tubular web close to the ground or even underground where it lays its eggs, sleeps by night, and hides out in bad weather. It doesn’t use its web normally for catching prey. It hunts using its excellent eyesight — some observers say that its eyes follow them — and its ability to leap. They have four pairs of eyes that give 360 degree vision and highly accurate distance measurement.

The spider doesn’t have muscles to extend or contract its legs for jumping the way mammals and some other insects do. Instead, it uses blood pressure. It drops its internal blood pressure suddenly, contracting its legs, and then manages an explosive blood pressure rise which extends its legs and projects the bug up to 50 times its body length. Given that its body length is only about a centimeter, that’s not a fearsome jump by human standards, but it’s easily enough for the spider to capture all kinds of bugs to feed on. Before it jumps, it attaches a silk line to its starting point and spins it out as it leaps. In case the jump fails, it climbs back up the thread to safety.

Females are bigger than males and males have to be careful when their mate invites them for dinner. The spiders are a favorite food for birds, but the spiders look very similar to mutillid wasps that have a very painful sting, and they may be confused with the highly venomous Redback Spider  (Latrodectus hasselti), so the birds need to be careful.

The Red-backed Jumping Spider is not aggressive to humans unless forced to defend itself; its bite is annoying but not serious. This spider has an affinity for grape vines and is a bug of concern for the grape industry. There is an active commercial trade supplying people who keep spiders as pets. For reasons not immediately clear, NASA sent one of these spiders into space in 2012.

More about them: Wikipedia (1) Wikipedia (2) USA Spiders SpiderIdentifications JumpingSpider.net TableGrapes Phipps

Tomorrow: Warrior Grasshopper

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