Jumping

December 27, 2021

Since it was warm last week, I thought it might be a good time to do some cleanup in my garden and refill the bird feeders.  As I suspected, all five of my feeders were empty, although there was a bit of corn log left that I had attach to the side of the squirrel feeder box.  As I approached the box to refill it, I noticed a flash of white on a small black spider.  The spider had just come out of the entrance hole in the side of the box and was working its way around toward the back.  I had seen these spiders previously but thought they had all gone into hibernation for the winter.  Apparently, the warmer weather had brought this one back into the open and it was hunting for a meal.

When I looked online, I found there are a variety of species of black and white jumping spiders of the family Salticidae.  The Jumping Spider (Phidippus audax) is the most common species and is found around the house or in gardens.   As of 2019, the Salticidae family contained over 600 described genera and over 6,000 described species, making it the largest family of spiders at 13% of all species.  Jumping spiders have some of the best vision among arthropods and use it in courtship, hunting, and navigation.  Although they normally move slow and unobtrusively, most species are capable of very agile jumps.  These jumps are usually when hunting but can also occur in response to sudden threats or when crossing long gaps.  Jumping spiders have both book lungs and a developed tracheal system and they use both (bimodal breathing).  Jumping spiders are easily recognized by their eye pattern, as all have four pairs of eyes with the anterior median pair being particularly large.  Jumping spiders are generally carnivorous but many species include nectar in their diets.  They are not venomous to humans.

Jumping spiders use their excellent vision to stalk their prey.  The eyes cannot move which causes the spider to move (sideways hop) its entire body to look at what it wants to see.  However, it can move the retinas of its two main eyes on the inside of the eye, so the center of the eye’s picture can be moved.  This trait gives the jumping spider binocular vision.  Very few species of jumping spider make a web, and instead use their silk for a safety rope while hunting.   The silk is also used to make a kind of tent where they sleep at night, shed their skins (molt), lay their eggs, and hibernate during winter.  This one was awake.

Thoughts:  Jumping spiders can climb glass and other smooth surfaces using the sticky hairs (scopulae) on each foot that hold onto the surface.  The ends on each hair are held to the glass by Van der Waals forces.  The van der Waals force is named after Dutch physicist Johannes Diderik van der Waals and is a distance-dependent interaction between atoms or molecules.  This adhesive force is also used by geckos who have microscopic projections (spatulae) which cover the hair-like setae found on their footpads.  In May 2014, Defense Advanced Research Projects Agency (DAPRA) demonstrated the latest iteration of its “Geckskin” technology by having a 220-pound (100 kg) researcher with 44 pounds (20 kg) of recording equipment scale a 26-foot (8-metre) glass wall using only two climbing paddles. Tests are ongoing, but DARPA hopes one day to make the technology available for military use, giving soldiers Spider-Man-like abilities in urban combat.  Now if we could only develop those cool shooting webs.   Follow the science.  Change is coming and it starts with you.