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Why do the leaves turn colors in the fall and what’s with the woolly bear caterpillar?

Post Date:10/01/2019 4:18 PM

By: Lorelei Elkins

fall 1Every autumn we wait patiently for the beautiful fall color to unfold - the mixture of oranges, yellows, reds and purples that dress mother up in her showiest colors.  A poetic way of saying, it all comes down to chemistry.  When the leaves are green during the spring and summer, they serve as factories where most of the food is manufactured with the help of a marvelous chemical called chlorophyll.

Through photosynthesis, the green chlorophyll absorbs energy from sunlight, transforming carbon dioxide and water into carbohydrate.  Come fall, the length of daylight diminishes and the chlorophyll starts to break down as there is no longer a need for food production.  As the green color begins to disappear other pigments present in the leaves become visible such as carotenes (orange) and xanthophyll (yellow).  Other chemical changes occur at the same time, which provide additional color through the development of red anthocyanin pigments, giving rise to the reddish and purple hues of sumacs and dogwoods. 

The weather also affects the intensity of leaf color, both temperature and water supply.  Low temperatures above freezing will favor anthocyanin formation, producing bright reds in maples, but an early frost will weaken the bright red color.  Rainy and overcast days tend to increase the intensity of fall colors, which means we might now get a great showing this year due to the dry conditions plaguing the southeastern part of the country.  The best autumn colors are seen when there’s been a warm, wet spring, a summer that’s not too hot or dry, and a fall with plenty of warm sunny days and cool nights.

Can Woolly Bear Caterpillars really predict winter weather? 

wolly bearThis fuzzy black and brown larval stage of the tiger moth makes its appearance in the early fall and has a shady reputation of being able to forecast the winter weather.  There’s even a Woolly Worm Festival October 19, 2019 in Banner Elk, NC! 

Whether fact or fiction, here’s how you can read the worm.  Folklore tells us that the wider the rust brown sections, the milder the winter will be.  If the black sections are larger, expect a more severe winter.  Between 1948 and 1956, Dr. C.H. Curran, a curator of insects at the American Museum of Natural History in New York City, set out to prove once and for all if this folktale had merit.  Amazingly enough, his research showed that there was a correlation between brown section length and milder than average winters.  However, Dr. Curran stated that the data sample was too small to be conclusive and it was more of an exercise for fun.  Could this be your child’s next science project for school?

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