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The Cracker Barrel: Surprising numbers

A few weeks ago, my wife purchased a book by Jim Gilbert titled "Minnesota Nature Notes." According to the blurb on the back cover, Gilbert has been observing the changing Minnesota seasons for more than 30 years, and has done it "with the accura...

A few weeks ago, my wife purchased a book by Jim Gilbert titled "Minnesota Nature Notes." According to the blurb on the back cover, Gilbert has been observing the changing Minnesota seasons for more than 30 years, and has done it "with the accuracy of a trained biologist and the rapt attention of a poet."

Having established a network of friends in all corners of the state to help him keep track of nature's progress, Gilbert then made it his business to share these observations on his weekly WCCO Radio call-in program, and eventually collect them together into this book.

Some of these insights are genuinely mind-boggling. Take, for example, his notes about rain.

"In an average year, thunderstorms will develop on 45 days in southern Minnesota and on about 30 days" in the north. About 90 percent of the moisture that falls upon the state is carried from ocean sources by moist air masses. The greatest amount of it comes from the Gulf of Mexico, but a small portion originates in the Pacific Ocean. Over an average year, he claims, the precipitation varies "from about 20 inches in the northwest to 32 inches in the southeast."

What I found astonishing about this is how much water that actually amounts to, and how much it weighs.

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"Looking at the numbers, it's interesting to see what one inch of rain amounts to on an acre of land. An acre of ground contains 43,560 square feet - that's about one football field of surface. A rainfall of one inch over one acre would mean a total of 6,272,640 cubic inches of water. This is equal to 3,630 cubic feet of water. A cubic foot of water weighs about 62.4 pounds, so the weight of one inch over one acre of land would be 226,512 pounds. The weight of one U.S. gallon of water is 8.345 pounds. Therefore a rainfall of one inch over one acre of ground would mean 27,143 gallons of water."

In parallel fashion, Gilbert's notes about spiders struck me as just plain fascinating.

"Spiders become more noticeable in August," he writes. "We become aware of their great diversity and encounter more webs, although we know that not all spiders construct webs. Those that do not build webs include wolf spiders - large, hairy, swift nocturnal hunters that chase down their prey; crab spiders, which ambush pollinating insects on flowers, usually in the daytime: and jumping spiders, which, as their name suggests, leap onto prey, usually during daylight."

More familiar to most of us are the orb web spiders of which the common garden spider is an example. These spiders weave large, vertical, conspicuous open webs with distinctive spokes. However, as Gilbert points out, "money spiders are probably more significant in control of insect populations. These small and inconspicuous creatures weave dense, often gossamer-like webs of many shapes in nooks and crannies of rock formations, in brush piles, around branches of plants, and in our homes. The cobwebs we see are most often those of money spiders."

Though many humans dislike and fear spiders, the fact is that they energetically pursue, seize and consume large numbers of insects. Without spiders, claims Gilbert, we would be overrun by insects.

"It is estimated that each year spiders eat enough insects to outweigh the entire human population," he writes. "If you think about how many mosquitoes it would take to equal your own weight (about 200,000 mosquitoes per pound), perhaps you would be a little friendlier to spiders."

Related Topics: THE CRACKER BARREL
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