許多種水蛭以脊椎動物或無脊椎動物的血液為生，有的或多或少地固定生活于一個動物的個體上，圭接近于體外寄生蟲；有的只是一時性的侵襲一下寄主，吸飽血液后掉下來；但也有屬于普通的掠食性或腐蝕性的。
以海南山蛭例，它的覓食行為如下:當(dāng)牛漸漸接近山蛭時（1. 5；米范圍），牛的身體發(fā)出的輻射熱、特殊的氣味和呼出的暖濕氣流刺激山蛭，它頭部開始轉(zhuǎn)向運動，身體前段左右擺動進行探測。
Hainan mountain vermiculite example, foraging behavior is as follows: when cows gradually close to mountain vermiculite (1. 5 meters range), bovine radiant heat from the body, special smell and exhale warm current stimulation mountain, it is turning to sports, head body swinging around the front.
隨著牛邊吃草邊接近，刺激越來越強，山蛭身體前段搖動加快，最后轉(zhuǎn)向牛的方向快速擺動，感覺到牛的方向和位置時，山蛭即停止擺動并快速向牛的方向爬行，幼體、亞成體或饑餓的個體爬得較快。
As the cattle are eating grass and close to stimulate more and more strong, mountain vermiculite recently moved to speed up the body, and finally to the direction of the cow fast swing, feel the direction and position, mountain vermiculite swing and quickly stop crawling towards the direction of the cow, larva and adult individual climb faster or hunger.