Thursday, October 31, 2013

Woolly Logic, Caterpillar Division

We found this guy on a path in Marymoor Park, Redmond, WA.
Just in time for Halloween, here's a caterpillar that dresses up as a tiger but is known as a woolly bear.

Woolly bears are found throughout North America, except in the most northern latitudes. They're one of the most familiar and well-liked caterpillars; it was fondly called a woolly bear even back in Colonial times. (Southerners, however, call them "woolly worms.") Thanks to its fuzz, this larva enjoys an affection not granted to its bare green and brown cousins.

Part of a woolly bear's appeal must also spring from its dogged caterpillar-on-a-mission behavior. Woolly bears catch our eye in autumn because that's when they trundle across sidewalks, paths, and roads, seriously boring ahead as if bearing important messages that must be delivered as soon as possible.

This woolly bear's curled-up self-defense certainly
dissuaded me from devouring it.
Nothing distracts a woolly bear from its task.

If you pick it up, it will coil tightly, under the assumption that you are a bird who wants to eat it but will give up once its potential meal turns into an unappetizing burl of bristles.

It will stay curled up until it figures the coast is clear, then will abruptly straighten out and resume its determined trek.

What these busy caterpillars are actually doing is looking for a safe place to hide for the winter. A woolly bear spends the cold months curled up under bark or tucked among rocks or logs. Its entire body shuts down, even its circulatory system. A natural antifreeze permeates its tissues, protecting it from damage in freezing temperatures.

Adult tiger moth, Wikipedia
In spring, the caterpillar emerges from this hibernation to spin a silken cocoon, shedding its bristles and incorporating them into the fabric, too. From this cocoon emerges the "tiger": a golden Isabella Tiger Moth.

The moth quickly finds a mate and lays eggs. In most of its range, this species hatches out into a spring generation of caterpillars that chow down on herbaceous plants (wild species, not garden plants or crops--probably another reason it's so well liked).

The spring generation then pupates, ultimately hatching into a second generation of moths that produces a second batch of caterpillars.

It's these summer caterpillars that chug across paths in fall, grabbing our attention with their cinnamon-and-black-velvet cloaks. They're also responsible for inspiring a charming bit of folklore: the width of a woolly bear's brown band is said to predict the severity of the upcoming winter. A wide band foretells a mild winter, while a narrow band warns of a harsh season ahead.

There's no scientific basis for this belief; studies haven't revealed any correlation between band width and weather. How much brown is on a caterpillar has more to do with its age: older caterpillars have wider brown bands. Caterpillars that feed in regions where fall weather has been damp tend to have narrower brown bands than caterpillars that frolicked in dry regions.

This woolly bear is not a woolly bear.
One of the first attempts at sussing out the relationship between bristles and blizzards took place in the 1940s and 1950s, when an entomologist named C.H. Curran spent some time collecting woolly bears, measuring their bands, and calculating the average.

According to the Old Farmer's Almanac, Curran was simply larking about while enjoying an excuse to take in the beauty of fall foliage in the Bear Mountain area of New York, knowing his sample sizes were too small to yield useful data. He, his wife, and his friends dubbed themselves "The Original Society of the Friends of the Woolly Bear." Apparently his caterpillars boasted relatively broad brown bands in those years, which were marked by winters that were milder than usual, confirming that the folklore was true in many people's estimations.

Of course, nothing (least of all scientific proof) will stop people from believing what they want to believe. Especially when it involves furry caterpillars. In some places it's thought that not only does the degree of brown banding foretell winter weather--the direction of caterpillar travel is a clue, too. A southbound caterpillar is telling you winter will be terrible, while a northbound one believes that winter will be mild. (That would mean peregrinations precisely prognosticate precipitation.)

"I'm heading south. No! North! No...wait..."
Although woolly bears are probably no better than TV meteorologists at predicting the weather, they're apparently aces at balancing their intake of toxic substances to rid themselves of parasites.

 A recent study showed that woolly bears infected with fly larvae (which rudely devour their host as they grow) increase their consumption of alkaloid-containing leaves, which kills off their unwanted guests.

If you just can't get enough of woolly bears, you can find woolly-bear festivals, complete with costume contests, woolly-bear races, and weather predicting, in several towns nationwide, including Vermilion, Ohio; Banner Elk, North Carolina; Beattyville, Kentucky; Lewisburg, Pennsylvania; and Oil City, Pennsylvania. Or start your own Society of the Friends of the Woolly Bear.

1 comment:

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