Running crab spider - the Philodromidae

I have photographed crab spiders before (click here), but those were flower crab spiders.  Those ones sit atop flowers and wait patiently for dinner to come to them.  The one above, a running crab spider, has a different MO but the same agenda.  It waits patiently for a meal to appear and then chases after it with great agility and speed.

This kind is very different, both in habit and body shape.  Flower crab spiders tend to have a larger abdomen and are not known for wasting energy chasing after prey.  Their front four legs are longer than the rear four and they work together to form a powerful trap which they overpower susceptible insects with.  Many a bee has been made a meal of by members of this spider family.  Running crab spiders, on the other hand, don't sit atop flowers, don't have two long front pairs of legs, and are often mottled shades of brown.  Neither of these groups uses a web for catching or holding prey; rather, they ambush prey efficiently.  Running crab spiders can quickly crawl over a plant; I found two of them and the first one was so adept at avoiding me or my camera that I never got a photograph of it.  Every flower crab spider I have ever photographed has been very complacent and acquiesced to my goals.

Running crab spiders are not true crab spiders at all.  They used to belong to the same family until 1975 and then received a different classification.  There are 90 species in North America, I have not identfified the one above.  One way to tell if a spider is a running crab spider is if the distance between the upper lateral eye and center eye is less than the distance between the two central upper eyes.  Of course, you can't normally see that without some form aid and they are not usually content to wait for your examination to be over.  See the image below.

Running crab spider and distance between eyes helps in identifying it.

These spiders may flatten their legs out to the sides and hug whatever substrate they are on to help them hide from both predators and prey.  

Sometimes the genus is referred to just as the running spiders.

Thanks for reading.

Eric Svendsen     www.ericspix.com

 

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