From the website:
The nightmare ram is the living spawn of a parasitic plant. It subsists on the salt of creatures which it metabolizes to power the glowing bulbs that grow atop its tough horns and the large lantern organ on it carries outside its body. They are sensitive, lonesome creatures that carefully cultivate beautiful, hidden gardens containing the plants that produce them. They will often beat trespassers into a pulp and use them as salt-rich fertilizer.
Like any fruit that has been picked, their life span is short.