I believe you are thinking about lignin digestion - an action of certain fungi, but its contribution to the end of the Carboniferous is debated. https://arstec

I believe you are thinking about lignin digestion - an action of certain fungi, but its contribution to the end of the Carboniferous is debated. https://arstechnica.com/science/2016/01/why-was-most-of-the-earths-coal-made-all-at-once/ https://arstechnica.com/science/2016/01/why-was-most-of-the-... As interesting as it would be, ants don’t seem to play a big role here.