Leeches are parasitic, terrestrial organisms that feed on the blood of other species. In "Genesis", the medical staff of the Terra Nova colony are shown using leeches to remove excess oxygen from colonists' bloodstreams. The buildup of excess oxygen in the human settlers is the result of previously living in a poor oxygen environment.
- Real leeches primarily dwell in leaf litter or murky water. When an animal passes by, they latch on using a powerful suction-cup-shaped mouth full of teeth and begin to suck blood. Their saliva prevents blood from clotting. The only safe way to remove a leech is to pull it off--if salt is sprinkled on it, as a common folk cure states to do, the leech may regurgitate semi-digested blood and its own saliva back into the bloodstream. Despite their reputation, no leech has ever been known to completely suck its host dry of blood.
- Some modern leech species can be very large, though not quite as large as the one in Terra Nova--see this page on the Giant Amazon Leech, or this video, for example.