adult Leeches achieve adulthood either when they reach their critical body weight or once they reach sexual maturity, depending on the type. The average adult leech is typically between 15 and 30 mm long, however, leeches as long as 200 mm have been found in tropical regions. Leeches die after reproducing once or, in some cases, twice. Nevertheless, leeches may live for months or a year prior to reproduction and can also survive the same length of time in between feedings.