SPIDERS CAN BE ENTERTAINING

by Whit Gibbons

October 2, 2016

For six weeks, from late summer to early fall, we didn't open our back door. This was not because we had put off fixing a hinge or hydraulic door closer. The decision was completely voluntary.

A giant spider had built a magnificent web across the entire glass door frame, and we did not want to disturb it. It positioned itself waist-high, which offered a perfect view from inside, providing us with a built-in nature show.

Our beautiful black-and-yellow visitor was a garden spider, also known as a writing spider or signature spider because of the conspicuous zigzags in the center of the web.

The exact function of the signature is unknown. One line of thought is that it stabilizes the web; another is that it serves as a visual warning so that birds and large insects avoid it, thus preventing them from destroying the web. Another proposed function of the signature is that the light reflecting on it actually attracts certain smaller insects, which become prey.

An intriguing part of ecology is that any or all of these hypotheses could be correct. Someone may eventually come up with an even better explanation.

Our spider was a female, as the ones that hold dominion over the web always are. The tiny males are seldom seen, and, after mating, they typically disappear entirely, which usually means they have become a meal for the female. In the scientific literature this mating strategy among spiders is referred to as "sexual cannibalism."

A female spider eating her mate is not aberrant but actually makes good biological sense. The male has no other function after mating so for the female to consume it is energetically practical. The male not only provides a meal for her but also does not deprive her of food by eating prey caught in the web.

We watched our impressive performer daily as she snared small moths and other insects. When prey became tangled in the web, the spider would rush over, bite it and then wrap the helpless creature in a shroud of spider web.

She got fatter daily. Then one morning she was thin again, still sitting in the center of the web. Off to one side of the door dangled an egg sac, a brown sphere the size of a golf ball. In late fall, or more likely in the spring, hundreds of young spiders will emerge from the egg sac and disperse.

We got to see an unusual performance during an afternoon rainstorm when she began jumping up and down on the web, taking down all strands that were near the ground.

Was this to keep the lower portion from getting wet and weighting the whole web down? Another ecological puzzle.

Then, one morning she was gone. Did one of the raucous backyard blue jays make a meal of her? Or was that simply the end of her own life cycle?

Upon investigation we found a new, slightly smaller egg sac alongside the first one. Was that her last hurrah?

Autumn is an ideal time to find spiders and their webs in the woods or around your yard. You may even be lucky enough for some to end up around your house. My attitude toward spiders is that unless it is a black widow, brown widow, brown recluse or some other species whose bite is known to be potentially dangerous, having spiders around is a good thing. They are compelling creatures to watch.

And, as with any animal, observing an individual over time can lead to interesting questions and speculations. You do not have to be a scientist to enjoy studying animal behavior. I assure you not everything is known about the ecology of any species, so you may even discover something new.

Now that we can open the door again, I keep eyeing the two egg cases in anticipation of having hundreds of baby spiders to entertain us next year.

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