Origin: English Folklore
About Shervage Worm
The Shervage Worm lived in Shervage Wood, gobbling up anything that came its way. An old woman who lived by picking berries couldn't pick with the worm there. It was as long as "three large oaks," and there's no way she can get around it. 
Then, one day, a woodcutter from out of town came by. She welcomed him, gave him food and cider, and pointed him in the direction of the woods. He didn't know about the worm, so he set off without a worry. However, the way was long and stony, so he eventually sat down on a huge fallen log to eat the meal he brought with him.  He was surprised when it began to wriggle, and he ordered it to keep still. The log didn't pay attention, so the woodcutter brought his axe down on it, and the axe went clean through it. Blood came out. The woodcutter said, "This log be sappy!" 
It was the worm he cut. Half went to Bilbrook and the other to Kingston. It never reunited, so it died.
The wurm was as long as three large oaks. 
- Newman The Hill of the Dragon
- Shervage Wood. Link defunct: <http://www.mysteriousbritain.co.uk/england/somerset/somerset8.html>
For more information on footnotes and references, please see the bibliography.