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Spider Spotting


This week's experiment is another that I did as a child. I must warn you that if you are afraid of spiders, you may not want to try this experiment. If you do, you may never leave the house again.

If you do want to try it, you will need:

  • a bright flashlight
  • a dark night
  • your yard

Spotting spiders at night is really quite easy. Go outside after dark. Turn on the flashlight and hold it at the side of your head, even with your eye. You want the beam to be shining at the spot where you are looking, and you want the source of the light to be as close to your eye as possible. Then look slowly around your yard, paying close attention to grass, flower beds, etc.

If you look carefully, you should see some bright pinpoints of light. Examine these carefully. Some of them will probably be drops of water clinging to the plants, but many of them will turn out to be the eyes of spiders. Depending on where you live, the weather, and how carefully you look, you may see a few spiders, or you may see hundreds of them. It is amazing how many spiders there are out there.

Why do their eyes shine? Spiders have a tapetum, a shiny layer behind the retina. Light passes into their eye, hits the retina, reflects from the tapetum and hits the retina again. This makes things look much brighter, making it easier to hunt at night. Many other animals also have this shiny layer in their eyes. That is why dogs, cats, deer, alligators, and raccoons all have eyes that seem to glow when you shine a flashlight at them. As I looked for spiders tonight, I found that many moths also have shiny eyes.

Whenever I point out spiders to people, they almost always ask whether the spider is poisonous. The answer is no. So far as I know, there are no poisonous spiders. There are venomous spiders. Venomous means that the creature's bite or sting is toxic. Poisonous means that it is toxic if you eat it. Surprisingly, in some parts of the world, spider is a delicacy. I wonder how they would taste if they were toasted and sprinkled on ice cream? I think I will stick to pecans and hot fudge.