Leeches are important to human being for so many reasons, which are as follows:
As food: Certain fishes, ducks, and other birds, turtles etc. eat leeches. Leeches are also used as bait to catch fish. Thus leeches form food of many animals which arc used as food by man.
As pests : Man faces both direct and indirect problems because of leeches.
(a) The leeches parasitic on fishes cause serious losses to fishery.
(b) Cattles, especially buffaloes, which pass considerable time in ponds, suffer due to leeches. The wounds caused by leeches become infected with bacteria and this causes crippling effect and death of cattle.
(c) Cattles and horses are often blinded by their attacks.
(d) The bite of Indian land leeches (very common in forests) is very painful. Due to their attacks horses are driven wild and men suffer serious loss of blood. The soldiers of Napoleon were put to serious trouble by leeches.
Medical importance: Leeches suck the blood of their hosts without causing pain. Due to this reason leeches were used extensively in the past for blood letting. It was believed in the past that removal of bad blood cures many diseases. Tribals still use leeches for this purpose. Hirudin as an anticoagulant remained in use in hospitals for a long time. However, it is not used now.