I learned about Trees with Knees from my Girl Scout camp counselor back when I was a very young girl. We were taking a tour of our tent unit when we found a tree similar to the one pictured here. “Pickles” explained that a long time ago, a seed landed on an old stump and began to sprout. Since it had not landed in soil, the roots had to grow over and around the stump to get to the forest floor. Over time, the “nurse stump” slowly rotted away, leaving the roots in their original positions – looking like the legs (with knees) of a strange, long-necked animal.
The first time I encountered this tree with a group at Audubon, I was surprised to discover they didn’t know what caused the “knees”. I had lived with this knowledge so long I just assumed everyone knew. When I gave the explanation and saw how amazed my group was, I realized that I had lots of that kind of knowledge that I could share… that there were plenty of things I had learned about the natural world over the years that might not be common knowledge… things people might be fascinated to know.
Another favorite misconception I love to clear up for people is the nature of that bump in the middle of some goldenrod stems. I’ve heard people call it a seedpod, or a disease… The truth is even more fascinating.
There is a fly that lays eggs on the stems of goldenrod in the summer. When a larva hatches, it bores its way into the center of the stem to find everything it needs to survive: food, water, and shelter. The plant responds to the activities of the larva by growing extra thick layers of tissue in the shape of a ball around it.
When fall comes, the larva creates an exit hole – right up to, but not breaking through the outer skin of the gall, then returns to the center to spend the winter. In spring, the larva will pupate and eventually use the exit hole to emerge as an adult. If you find a gall with a smooth small hole, the adult has emerged.
Sometimes the fly is not so lucky. There are too many creatures out there that know about this secret life. Birds, such as chickadees or downy woodpeckers, may peck holes into the gall to find a tasty lunch.
And, of course, there is the overzealous naturalist who finds a gall with no hole at all and wants to show her charges the contents. (Who me?)
Would you believe there’s more? For example, there are wasps that drill into galls to lay eggs so that the wasp larva can feed on the fly larva. It’s all too fascinating… and I never tire of teaching people about it! (While hiking with the Cub Scouts, we also found oak leaf galls and willow galls.)
P.S. After showing my Cub Scout group the gall, we happened on this water snake – the first I’ve seen in 2007. After I explained that while water snakes are not poisonous, I don’t like to pick them up, since their saliva has an anti-coagulant that keeps your blood flowing after they bite you, which they almost always do… one young Cub Scout decided he wanted to try picking it up anyway. His first attempt made the creature turn it’s head toward the boy, then slither a little way down the bank. That movement was enough to convince the dad that his son was not going to get a second chance.