This is from the onion, it's not really happening.
http://www.theonion.com/video/teens-migrating-from-facebook-to-comments-section,35583/

Actually he is doing a great deal of damage to those trees. The only part of the tree that is actually alive is the outer inch or so of the tree under the bark. That is where the nutrient and water transport system of the tree is located. So by hacking away a large portion of the tree he is essentially choking the tree by reducing the amount of water and nutrients that can be pulled up from the ground by the roots towards the upper branches. It is termed girdling. http://en.wikipedia.org/wiki/Girdling

Those aren't parasites, they are maggots.