The tiny Wool Sower Wasp stings a fresh young stem and deposits her eggs. The developing eggs use chemicals like hormones to stimulate the tree to produce a very specific growth structure that encases and protects the larvae. This growth is not a normal shape or color or texture of the tree – the growing parasites within the stem tell the tree to do this, and how to do it.
If you open the gall, the larvae look like seeds packed side by side with fuzzy tails. The whole cycle takes two years to complete. Though strangely parasitic, it doesn’t hurt the trees.
Though the gall protects the young larvae from predators, and even pesticides, there are other parasitic wasps that have evolved special ovipositors that allow them to pierce the gall and deposit wasp eggs on the wasp larvae.
Even parasites have parasites.