http://www.newsweek.com/vampire-bats-mexico-drug-cartels-desmodus-rotundus-medical-treatments-1299094

Mexican drug cartels are hindering the work of a group of scientists who are conducting research into the venom of vampire bats, as part of an effort to identify potential new treatments for a host of serious medical problems.

Common vampire bats (Desmodus rotundus)—which are found in Central and South America—feed exclusively on mammalian blood, often that of livestock, such as cattle. When they feed, the bats produce a venom which stops the blood of their victim clotting, enabling it to flow constantly, thus providing more food.