How powerful is leeches sucking blood?
Leeches can suck 2- 10 times their own weight at a time, and almost every leech in the pond has the opportunity and enough time to suck the largest amount of blood in three days and three nights. The total amount of human blood doesn't matter if it is 4000-5000 ml. Once the blood loss exceeds one-third of the total blood in the body, it will be life-threatening.