Animal Magnetism
Cooperative Cobs

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Cooperative Cobs

When I was growing up back in the Middle Ages, some people believed that while orbiform spider webs were woven by spiders, those random “cobwebs” you find everywhere (Walker's Third Law of Spiders: “You will never find the last cobweb in a room”) had nothing to do with spiders—they just spontaneously appeared, like dust bunnies. Now, even as a little kid, I had a strong belief in causality (it's weakened over the years), so it seemed obvious to me that if spider webs were made by spiders, cobwebs ought to be made by cobs! And indeed, I eventually figured out that wherever you found cobwebs, you almost always found either a daddy long-legs spider in residence (when you do, blow on it lightly and watch how it goes into a wild random swinging motion so a bird won't be able to nab it) or evidence of a departed perpetrator in the form of one or more shed exoskeletons. So, I started calling daddy long-legs spiders “cobs”, and I've done so ever since.

Here are two cobs (Pholcus phalangioides) sharing the same web. I thought these spiders were highly territorial. I've seen one kill and suck the yummy parts out of a big ole' ugly black meaty spider with a body five times as big. But these two seem to get along just fine. Maybe they're a happy couple or just good friends. The tiles in the background are 5 cm square.

The reason you always find so many cobwebs is that there are so many cobs—they are extremely prolific. Here's a proud cob mom and her brood, photographed in another bathroom a couple of months later. Yes, I ought to clean the bathrooms more frequently.

Mama cob and the kids
Kids—how many spiders are in this picture?   Don't forget to count mama spider!
Count the spiders     Didn't work?   Try this.

The photo of the two cobs sharing a web was taken by John Walker on July 6th, 2003 with an Olympus C-3040 digital camera with automatic exposure, focus, and flash. The picture of mama cob and the kids was taken on August 21st, 2003 with the same camera in all-automatic macro focus mode. No spiders were harmed in the production of these images.

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by John Walker
August 25th, 2003
This document is in the public domain.