I still cannot get over the wonder and mystery of what gall wasps can do to plants. This is bio-engineering! The wasp lays her egg and somehow the plant makes a structure that is not a fruit, it is not a seed, it is not a leaf or stem. It's a wholly recombinant architecture customized to the needs of the growing young larva. The plant provides food and shelter-- It's like a cancer, but with a purpose.

How did it evolve? How is it done!?

(Photo by Timothy Boomer, https://wildmacro.com/)