Hematophagy (sometimes spelle haematophagy or hematophagia) is the habit of certain animals of feeding on blood (from the Greek words, haima "blood" and phagein "to eat"). Since blood is a fluid tissue rich in nutritious proteins and lipids that can be taken without enormous effort, hematophagy has evolved as a preferred form of feeding in many small animals such as worms and arthropods. Some intestinal nematodes, such as Ancylostomids, feed on blood extracted from the capillaries of the gut and about 75% of all species of leeches (e.g. Hirudo medicinalis), a free-living worm, are hematophagous. Some fish, such as lampreys, and mammals, especially the vampire bats, also practice hematophagy.