Quassia, also known as Jamaica Quassia and Bitter Wood, is a small, shrubby tree native to the West Indies. Its species name, amara, is derived from the Spanish word amargo, which means “bitter.” The name fits since the bark of the tree contains quassin, a substance 50 times more bitter than quinine. In fact, it’s the bitterest naturally-occurring chemical known to exist. Although quassia bark is an ingredient in herbal bitters in moderate amounts, the presence of this highly bitter phytochemical makes infusions made with this herb very effective natural insecticides.