An artichoke gall on an oak tree photographed by DKG last week. The artichoke gall wasp (Andricus foecundatrix) lays its eggs in the leaf buds of an oak tree; the egg and the growing larva produce chemicals that force the tree’s extraordinary outgrowth.
Southwick Country Park Nature Reserve 
How does the oak tree do this, it’s unlike anything it would normally produce?
I have changed the post slightly to reflect that fact that the growth of the gall is initiated by the egg and larva, not by the tree. The egg and the larva produce hormone-like chemicals that force the tree to make the gall; the gall’s purpose is to provide nutrition and shelter tailored to the species of the wasp. Think of it as hacking: the egg and the larva have hacked into the tree’s growth. The products of photosynthesis are hijacked and concentrated into the gall’s tissue for the larva to feed on. Very clever.
This is fascinating! I’ve just been googling to find out more!
Google is your friend if you are an enquirer after biological truths but if your questions are political, approach with caution.
Agreed.
I figure I’m safer with trees than politicians lately…
These are the delicate interactions between species that we mess with at our peril. We are destroying stuff before we even know how it works.