The leech feeds on liquid food, and the blood from the animals is not enough. While still in the cocoon, embryos feed on coconut organic matter, babies and young leeches feed on aquatic plant mucus, unicellular cilia, aquatic insect larvae, worms and small shells.
The adult leech feeds on blood, as their teeth can now pierce the skin with more mucus, as well as the hard skin of all animal species. Leeches are extremely greedy and can drink blood even when their stomachs are full of undigested blood. When not fed, hungry leeches lose weight quickly.
Centuries of practice with leeches show that adults have difficulty consuming anything other than blood. They are adapted to withstand prolonged periods until the right food appears. In clean water, leeches lose more than a quarter of their body weight when not fed, but cannot live without food anyway. When they are hungry, they throw themselves at the first piece of rotten or dead meat, or at another leech, despite the unpleasant odor it acquires after the blood is processed in its body. This is why such leeches are prey. other hungry leeches immediately after being fed. Cannibalism is especially common in horse leeches. When they are hungry, they attack larger animals, consuming their blood, sometimes until the latter's death.
Medical leeches can suck blood from all types of vertebrates. When some of their blood is drunk, in many cases the victim dies. For this reason, leeches belong to the group of predators. It is said that ten hungry leeches are able to kill a horse. When they have nothing else to eat, they attack fish or frogs, very rarely reptiles.
Leeches have extra wide stomachs, which serve as reservoirs for excess blood. Therefore, when the leech is well fed, it must process the blood it has drunk for at least half a year. In medical leeches, this period is the longest. It can live from 1 to 3 years without eating.
Leeches can suck three times more blood than their body weight. It feeds even when there is still a lot of undigested blood in the stomach. Sometimes a leech happens to die from food if it does not grow. The blood is processed in their body very slowly, because it takes a long time for their own enzymes to break down the protein in the stomach and intestines. When their blood supply is depleted, they can continue to live a long time without any food, due to well-developed connective tissue, which is rich in reserve substances. It all depends on the age and condition of the leech, how much blood it sucked, the season, etc. Hungry leeches grow very slowly and therefore need to be supplemented with artificial growth.