I took this photo on a recent walk along the bank of the River Deben at first we thought the tree was being taken over by some strange parasite. We have since discovered that it is a growth, called a gall is formed by the tree
in reaction to chemicals released by the larvae of the Gall Wasp, which incites plant hormones to form the gall. The hatching larvae live inside the Galls nourishing themselves on the tissue of the galls, well protected from elements. In the Autumn when the tree sheds its leaves the Galls drop as well where it lies until the spring arrives and the Gall wasp emerges.
How amazing is that? That an insect can induce a tree to grow it a safe refuge!
However, the plot does thicken, some other wasps use their long, hardened egg-laying tube (ovipositor) to bore into the gall and lay an egg on the helpless gall maker which in turn becomes food for the larvae of the parasitoid.
[embedyt] https://www.youtube.com/watch?v=CzXccvoJThI[/embedyt]
