out of subject but somehow related...
Scienceray has a great, photo-heavy feature on the humble gall, a kind of woody egg-sack that incubates a parasite -- bacteria, mites, fungi and insects. They can look utterly Martian, or like something from the realm of faerie. And they can get to be the size of cats.
The Abnormal, Gruesome Gall - Alien Invader in Your Yard