Caterpillar Meteorologists: Woolly Bear Winter Weather Forecasters

Summary: The myth of woolly bear winter weather forecasters dates back to Colonial America's association of woolly bear middle band length with mild/severe winters.

Coloring suggests mild winter? woolly bear caterpillar (Pyrrharctia isabella); west side St. Paul, east central Minnesota; Sept. 17, 2014: Courtney Celley/USFWS Midwest Region (U.S. Fish and Wildlife Service-Midwest Region), CC BY 2.0, via Flickr

The mystique of woolly bear winter weather forecasters traces to eight annual studies conducted at Bear Mountain State Park from 1948 to 1956 by Charles Howard Curran, Canadian-born insect curator and true flies (Diptera) specialist at the American Museum of Natural History from 1928 to 1960.

On Wednesday, Oct. 27, 1948, American Museum of Natural History entomologists Mont A. Cazier and Charles Howard Curran, accompanied by their wives, journeyed forty miles away from New York City to Bear Mountain State Park. The expedition collected 15 woolly bear caterpillars (Pyrrharctia isabella) at the park and measured the lengths of the caterpillars’ rusty brown middle bands and black end bands. With this carefully obtained data, the expedition’s leader, Dr. Curran, sought to test a popular myth about woolly bears as caterpillar meteorologists.

According to weather folklore dating back to Colonial America, the bands’ comparative lengths predict the mildness or severity of the upcoming winter. Narrow brown bands indicate severity while long brown bands foretell mildness.

The first expeditionary survey was announced in an article by seasoned news reporter John O’Reilly on the front page of the next day’s issue, on Thursday, October 28, of The New York Herald Tribune. O’Reilly’s article about the second annual survey almost one year later reminded readers of the first annual survey’s accurate forecast of “extremely mild” for the 1948/1949 winter. A later headline celebrated woolly bear meteorology: “The Woolly Bears Are 100 P.C. Right -- So Far.”

Woolly bear winter weather forecasters blend with autumn’s colorfully earthy landscapes as they conspicuously pursue a diet of grasses and leaves. Prior to hibernating, woolly bears wander extensively. Undaunted by distances, they are capable of logging speeds of four feet (1.2 meters) per minute. Seldom known as crop or garden pests, woolly bears tend not to disconcert farmers and gardeners.

Woolly bear winter weather forecasters overwinter in such sheltered spots as leaf piles, logs, and rocks. Woolly bear winter weather forecasters freeze along with winter’s freezing temperatures. Cryoprotectant, a natural, sugar-based antifreeze produced in woolly bear tissues, allows woolly bears to survive the plummeting temperatures characteristic of their North American homelands.

With spring’s thaw, woolly bear caterpillars switch to the pupal stage for their transformation into black-spotted orange Isabella Tiger moths (Pyrrharctia isabella).

Last week, on Tuesday, Jan. 19, a woolly bear, curved into a tight comma, greeted me when I opened my home’s east-facing front door. The woolly bear was lying on the cold cement of the front porch, a few inches from the south side of the tan woven jute door mat that has been a favorite of many generations of woolly bears over the past decade. As I picked up the quiet woolly bear to relocate it to safety on the mat’s northwest corner, it slightly moved. I noticed that its brown band accounted for about two-thirds of its 13 segments.

It has been a mild winter so far, in stark contrast to last winter’s three successive huge snowfalls in February. So, no cold winter this year? Is that what you’ve come to tell me? I thought.

The woolly bear was gone the next day. Two days after that, the busyness of modern life came to a standstill as snow fell and fell and fell in fulfillment of the forecast of a Winter Storm Jonas-driven blizzard.

Was the woolly bear winter weather forecaster wrong? Perhaps not. Strong winds never materialized; snowfall measured half the predicted amount; the blizzard lasted one day, not two. On Sunday, temperatures predicted at lower- to mid-30s Fahrenheit, with wind chills, instead rose up to the lower 40s, with clear blue skies, no noticeable wind chill and warming Sun.

woolly bear caterpillar in Montreal, Quebec; Sept. 24, 2006, photo by IronChris: NY State Parks @NYstate parks via Twitter Oct. 27, 2014

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Coloring suggests mild winter? woolly bear caterpillar (Pyrrharctia isabella); west side St. Paul, east central Minnesota; Sept. 17, 2014: Courtney Celley/USFWS Midwest Region (U.S. Fish and Wildlife Service-Midwest Region), CC BY 2.0, via Flickr @ https://www.flickr.com/photos/usfwsmidwest/15091470159/

woolly bear caterpillar in Montreal, Quebec; Sept. 24, 2006, photo by IronChris: NY State Parks‏ @NYstateparks via Twitter Oct. 27, 2014, @ https://twitter.com/NYstateparks/status/526756543971491840

For further information:

1999 Old Farmer’s Almanac. “Predicting Winter Weather: Woolly Bear Caterpillars.” The Old Farmer’s Almanac.
Available @ http://www.almanac.com/content/predicting-winter-weather-woolly-bear-caterpillars

Carver, Susan. “The Folklore of the Woolly Bear.” New York State Parks’ Nature Times > Flora and Fauna. Sept. 29, 2015.
Available @ http://nysparksnaturetimes.com/2015/09/29/the-folklore-of-the-woolly-bear/

CMHARRIS86. “The Legend of the Woolly Bear.” The Ecotone Exchange. Nov. 6, 2013.
Available @ http://theecotoneexchange.com/tag/dr-c-h-curran/

“Dr. Howard C. Curran.” American Museum of Natural History > Invertegrate Zoology > Historical Staff.
Available @ http://www.amnh.org/our-research/invertebrate-zoology/staff/historical-staff/dr.-howard-c.-curran

SiFri. “The Myth of The Woolly Bear.” YouTube. Nov. 7, 2013.
Available @ https://www.youtube.com/watch?v=Ca-XZdSAxzo

NY State Parks‏ @NYstateparks. "Have you seen a Woolly Bear? This caterpillar is thought to predict winter weather. Find out." Twitter. Oct. 27, 2014.
Available @ https://twitter.com/NYstateparks/status/526756543971491840

O’Reilly, John. “Woolly Bear Survey Indicates a Mild Winter." New York Herald Tribune. Thursday, Oct. 28, 1948.