Monday, October 10, 2005

Arachno-lunch

At the end of today's lunch on the office patio, my colleague noticed a mysterious object on the frame of the picnic table umbrella. At first it looked like a leaf or empty seed pod, but on close inspection we saw what looked like two spiders joined at the legs. The top one appeared to be dried up and the bottom one was very pale. Perhaps it was two dead spiders.

But after a minute or two, the bottom part of the object moved a little, and we realized what we were seeing: a spider shedding its old exoskeleton (molting). Another minute later, the spider was free. It was quite pale, and slowly pulled itself up to the frame to rest. It was the same type of spider that has been making webs all over my garden and around the office patio. Through some web research, I'm guessing that is Araneus Diadematus, sometimes called 'garden spider.' Later in the day I stopped by to see if anything had changed, and the spider was still in the same place, resting and hiding.

Spiders have an exoskeleton that can't expand as the creature grows, so they periodically shed the exoskeleton and form a new one. The new exoskeleton is folded and somewhat flexible, allowing a burst of growth after the molt. But the flexibility brings vulnerability, so the spider might stay in hiding until the exoskeleton has reached full hardness.

Some excellent photographs of the molting process can be seen at the Photography by 'Pong. There is a more extensive description of the molting process at howstuffworks.

Some other links: Nick's Spiders, nwspiders, University of Paisley Biodiversity Reference, Animal Diversity Web.

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