Wednesday, July 31, 2013

Red-backed Jumping Spider

The picture on Friday's blog is a facial view of a spider showing two big eyes like headlights, two smaller eyes to the side (turn indicators?) and four small eyes across the top.  Taken with my pocket Lumix, the picture lacks the clarity of the big league photographers but I suspect some of you recognized it as a spider.  The blue-green structures are the chelicerae, hollow mouth parts which connect the venom glands to the fangs at the tips.

Kevin Firth emailed within 4 hours with an ID as a jumping spider of the genus Phidippus.  I was amazed because spiders are tough except some of the more distinctive species.  I have contacted a lot of entomologists over the last few years, and even they sometimes ask if I know a "good spider expert."

Some species can be narrowed down by their web construction, habitat and body shape.  My specimen jumps dramatically, which is how I spotted it in Brian Edmond's dense prairie plantings. The final ID as red-backed jumping spider, Phidippus clarus, was made from browsing through jumping spiders in Bugguide, and comparing each with my full body photograph.

There is a lot of information on P. clarus on the web, particularly on Wikipedia.  Some of it is highly technical but there is also a lot of gee-whiz facts.
  • Those big eyes really work.  Their vision exceeds that of a cat and is 10 times greater than the dragonfly which is the most acute of all the insects.
  • Their powerful back two sets of legs allow them to jump 50 times their length, the equivalent of my jumping 250 feet.
  • "In an experiment, P. clarus was offered as many fruit flies as it could eat, and in four-hour sessions individuals took 17 flies on average – while one took 41."
  • Males compete for the largest females which then produce the largest number of offspring.  "When P. clarus males compete for females, the winners are those that produce the most vibrations on the surface and those that are largest. Contests between females involve less displaying, and physical fights between females are more likely to end in injury or death. " Mating rituals are complex and the average female produces 135 eggs in her sac.
  • They hunt by sitting at the top of vegetation and pouncing down on their unsuspecting prey.  They, or their egg sacs, are placed sometimes in agricultural settings to feed on plant pests.
All spiders have silk glands which we associate with webs but some have adapted them to other uses.  The jumping spiders make silk shelters for protection of their eggs and a safer place to hang out while they are molting.

You can see a video of male and female P. clarus on this link.  Arachnophobes beware.
An extensive collection of jumping spider videos can be found at this Dick Walton Natural History Services link.