Identify this orb weaving spider.

September 3, 2009 10:05 AM

Spider identification. Outside my ground floor window a spider has set up shop in a corner. It's an orb weaver, but it does something I've never seen before.

It has made an orb web 25-30 cm in diameter. The largest openings at the edge of the orb are about the same size as the spider. It doesn't sit in the orb though. Instead it has also made a sort of blind up against the window frame, and it hides behind it. It backs into the blind and appears to peek out over the top. Whenever something hits the web it rushes out to the center and systematically plucks on the strands. It appears to be testing "sectors" of the web to precisely locate where something has gotten caught. If it's food it wraps it up and takes it back to the blind. If not food it cuts out whatever is stuck and repairs the web. The spider is about 1 cm across. I don't know if it has any markings since it moves really fast, and I can't see it's back. It's behavior is remarkably stereotyped and has incredible economy and precision. Is it an Aculepeira species? That's the closest I could find, but I couldn't find a whole lot of information. The spider and I are in the northwest US.

posted by sevenless to pets & animals (3 answers total)

I have seen spiders "pluck" or vibrate their web like this. Just guessing here, but I think it keeps their prey off balance, bouncing their wings, legs, etc., into contact with more web.
posted by weapons-grade pandemonium at 10:23 AM on September 3, 2009

I took an arachnology class in undergrad (yes, it was awesome), and from experience I can say identifying spiders down to the species can be tough without actually seeing them up close. Indeed, sometimes you need a magnifying lens to pick out certain distinctions.

That said, as an orb weaver, its most likely in the family Araneidae. Your best bet for identifying the spider might be an expert familiar with the local species - and it looks like there is one nearby.
posted by dicaxpuella at 10:39 AM on September 3, 2009

Lots of Araneidae species do this. It's called a retreat. A common genus is Eriophora. If you manage to take a photo, mefi mail me. Aculepeira as well as Metepeira are known to build retreats, so it's possible.
posted by dhruva at 1:05 PM on September 3, 2009