Charles Darwin's last book, The Formation of Vegetable Mould Through the Action of Worms, was about the importance of worms. Taking a page out of Darwin's book, Pro-Organic Belize invited self-described worm farmer Graham Herbert to talk on Earth Day about his 100% organic fertilizer, made in Belize, worm castings. The 'wormiculture' expert explained that use of worms to build up soil is properly called vermiculture.