The Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, narrated to me from Ahmad ibn Muhammad, from his father, from al-Husayn ibn al-Hasan ibn Aban, from al-Husayn ibn Sa'id, from Ibn Sinan, from Ibn Maskan, who said: I asked Abu Abdullah عليه السلام about things that fall into wells. Imam عليه السلام said: "As for a mouse, water should be drawn from it until it becomes clean. If a dog falls into it, and you are able to draw out all the water, then do so. But anything that falls into the well and does not have blood - such as scorpions, beetles, and similar creatures - there is no harm."