Sunday, September 26, 2004

Spiders From Mars

The kids and I were looking at spider webs this weekend. We have a couple of persistent garden spiders in the front yard. One has been building webs near the side of the driveway all summer long. One time it built a web stretched from a shrub onto the side of our minivan. On Saturday its web stretched across the walk to our main entrance. We had to knock down the long end of the web to get by. The web partially collapsed and the spider scurried away. This morning he was back with a new web.

This time his web avoids crossing the walk. He had flung his line up into the ornamental cherry tree. It's amazing how light and strong spider web lines are.

How do spiders create such huge, complex webs working alone at night? It's a clever piece of engineering programmed into the spider's brain. Here's an animation that shows how the spider gets started and lays out the web. The web begins when the spider tosses out a long line and waits for it to stick to something. Wherever it sticks, the web gets built. There's a lot left to chance. The spider's diet depends on a random harvest of bugs flying through its web and getting snared. In a sense, a spider is the ultimate entrepreneur. No bugs and the spider dies. But sometimes they score big.

A second spider has a web between a shrub and our house. Same species. We noticed that he would either stand in the middle of the web or hide under a ledge. In the latter case, he had a line tied to him and whenever anything touched the web he would instantly spring out and investigate. A bug in the web would get wrapped up in seconds and left on the web. A leaf or other debris would be cut from the web and discarded. Last night he caught something really big.

It's a little hard to see. The spider is under the ledge. It's not clear what he caught. It's wrapped up in silk. Maybe a large fly? He still has a line connected to the web but he ignored any web activity. There were a couple of small flies caught in the web. He probably had enough food for the rest of the season.

Talking about spiders reminds me of an essay I read in a Psychology course in college. Scientists gave psychoactive drugs to spiders. The spiders would spin their webs in different ways depending on the drug. Spiders given marijuana made a reasonable stab at spinning webs but appeared to lose concentration about half-way through. Those on speed would spin their webs with great gusto, but apparently without much planning leaving large holes. You can see examples of the drug-altered webs here. Note: The spider specialist from the Natural History Museum in London who's quoted in the article, Paul Hillyard is the brother of someone I used to work with. I remember thinking how odd it was to devote an entire career on spiders. Now, years later, here I am writing about them.
posted by Bob at 9/26/2004 06:00:00 PM  | | digg | del.icio.us | reddit