Charlotte’s Web

“Fern was up at daylight, trying to rid the world of injustice. As a result, she now has a pig.”

From Charlotte’s Web, by E. B. White

Intermediate Physics for Medicine and Biology never mentions spiders like Charlotte, does it? It does! Chapter 1 has a homework problem about the strength of a spider’s thread. Steven Vogel discusses this in his terrific book Life’s Devices.

Anything with a strength at or above 100 MPa has to be considered a good tensile material-wood with the grain and collagen have about this value. Nylon [1000 MPa] is outstanding… and spider silk [2000 MPa] is superb-one can only wonder why, if one kind of creature can make a protein this good, the others, with the same synthetic machinery, don’t do as well.

The analysis of spiders in IPMB cites the paper:

Köhler T, Vollrath F (1995) “Thread biomechanics in the two orb-weaving spiders, Araneus diadematus (Araneae, Arcneidae) and Uloborus walckenaerius (Araneae, Ulobordae),” Journal of Experimental Zoology, Volume 271, Pages 1–17.

Their introduction (below, with references removed) explains how biomechanics is critical for spider webs.

Orb-weaving spiders within the Araneoidea are some of the most diverse and abundant predators of flying insects. As such, orb-weaving spiders depend upon their webs to stop the massive kinetic energy of flying insects and retain those insects long enough for the spiders to attack and subdue them. An orb web consists of a framework of stiff and strong radial threads that supports a spiral of sticky capture silk, the primary means by which prey adhere to the web. In addition to being covered with viscous glue, capture silk is also highly extensible, which allows the silk to gradually decelerate intercepted insects, thereby preventing prey from ricocheting out of webs. Thus, the potential for an orb web to retain prey long enough to be captured by the spider depends intimately upon the mechanical properties of these capture threads. Araneoid capture threads are composite structures that consist of two parts: a core pair of axial fibers spun from flagelliform silk and a surrounding coating of aqueous glue spun from aggregate silk glands. The aggregate silk secretions make capture threads sticky and can modulate the mechanics of the flagelliform axial fibers. However, it is the core axial fibers that provide the primary tensile mechanics of araneoid capture threads.

One of Garth Williams’s radiant drawings from Charlotte’s Web (above) makes me suspect that Charlotte was an orb-weaving spider.

When Charlotte’s children were babies, Wilbur (some pig) witnessed them engaged in biological physics.

Then came a quiet morning when Mr. Zuckerman opened a door on the north side. A warm draft of rising air blew softly through the barn cellar. The air smelled of the damp earth, of the spruce woods, of the sweet springtime. The baby spiders felt the warm updraft. One spider climbed to the top of the fence. Then it did something that came as a great surprise to Wilbur. The spider stood on its head, pointed its spinnerets in the air, and let loose a cloud of fine silk. The silk formed a balloon. As Wilbur watched, the spider let go of the fence and rose into the air.

“Good-bye!” it said, as it sailed through the doorway.

Mark Denny describes this behavior in Air and Water.

The young of some spiders exhibit a remarkable behavior in which they climb to the apex of a blade of grass, extend their abdomen into the wind, and pull from their spinnerets a skein of very fine silk fibers. The drag on the fibers is sufficient to carry the young aloft, and Darwin reported having these “ballooning” spiders land on the while still many miles at sea.

I also enjoyed the animated musical of Charlotte’s Web with Paul Lynde as the voice of Templeton the rat.

When I was in third grade, my teacher Miss Sheets read Charlotte’s Web to my class, one chapter each day. I remember sitting at my desk crying when Charlotte died.

E. B. White was an excellent writer. In addition to his children’s books Charlotte’s Web, Stuart Little, and The Trumpet of the Swan, he was coauthor with William Strunk on the famous writing manual The Elements of Style (“Omit Needless Words”).

The closing line of Charlotte’s Web reminds me of Barry Bowman, my humble friend who helped me become a better writer.

“It is not often that someone comes along who is a true friend and a good writer. Charlotte was both.”

Originally published at http://hobbieroth.blogspot.com.

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Brad Roth

Brad Roth

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Professor of Physics at Oakland University and coauthor of the textbook Intermediate Physics for Medicine and Biology.