Skip to content

This morning when I was talking on the phone with my sister outside, I noticed a spider wrapping up a fly it had caught in its web. I recognized it immediately as a cellar spider, Family Pholcidae, because of its slender body, long legs and the tangled shape of its web. It also has dark markings on the underside of its body.

The larger cellar spiders common around homes in the Southwest have been introduced from Europe. This one looks like the marbled cellar spider, Holocnemus pluchei, because of the marbled white and pinkish-red pattern on its abdomen.

cellar spidercellar spider 2

We have a community of cellar spiders that live on the outside of one of the windows where we watch our bird feeder. When the feeder is quiet, we watch the spiders instead.

After finding the infrared photographs last week of a cat with hot feet, I started thinking about the temperature of body extremities in cats. You see, there is a “cool” example of how the environment can change what an animal looks like and it involves cats (although the same phenomena is also found in rabbits and mice.)

Ever seen a Siamese cat? These cats are light colored with darker feet, ears and noses. It turns out their color is due to a mutation in the gene that produces brown color (the protein melanin), called the Tyrosinase gene. At normal body temperatures the coat color of an animal with the Siamese variation is light. At slightly lower temperatures, such as occur on the animal’s extremities, the normal dark brown pigments are produced. Conventional wisdom says when a Siamese cat is raised in a cold climate, such as Northern Canada, it will have more extensive brown on its legs, tail, nose and ears than a Siamese raised at the equator.

Now go back and look at the infrared photograph of the cat at the infrared zoo. Are the extremities cooler? Seems to be a contradiction here. Any ideas why? Where do you think this Siamese cat in this picture from Wikimedia Commons was raised?

If you are looking for a way to find some science fun on the computer this week, try this link to the Infrared Zoo at http://coolcosmos.ipac.caltech.edu/image_galleries/ir_zoo/. It is a gallery of infrared images of various animals. I particularly like the Hide and Seek Game, because it gives more details about each image (just click on an image once it appears).

Looking at the images made me think about cold-blooded versus warm-blooded animals. I was surprised to see the cat had warm feet, because I always thought an animal's extremities were the coolest parts. Of course, the extremities give off the most heat when the animal is too hot.

Have fun exploring this site!