Spanish Moss is an epiphytic plant, which grows on another plant, but does not rely on the host plant for nutrients; epiphytes make their own food by absorbing nutrients (especially calcium) and water from the air and rainfall. Spanish moss is colloquially known as “air plant”. It can grow so thickly on tree limbs that it gives a somewhat “gothic” appearance to the landscape, and while it rarely kills the trees it lowers their growth rate by reducing the amount of light to a tree's own leaves. It also increases wind resistance, which can prove fatal to the host tree in a hurricane. See my 1/21/10 photoblog pictures of trees with Spanish Moss.