(Genesis 37:24:) "And they took him and cast him into the pit, and the pit was empty; there was no water in it." There was no water in it, but there were serpents and scorpions in it. What did Simeon do? When they put him into the pit, Simeon would give the command, and they would cast great stones upon him in order to kill him. But when he fell into Joseph's hand, Joseph would throw fattened fowl upon him.
Serpents in the Pit and Joseph's Mercy Toward Simeon
Midrash Tanchuma Buber, Vayeshev 13:10
ויקחהו וישליכו אותו הבורה והבור רק אין בו מים. מים אין בו אבל נחשים ועקרבים יש בו, מה עשה שמעון כיון שנתנו אותו לתוך הבור היה שמעון מצווה ומשליכים עליו אבנים גדולות כדי להורגו, אבל כשנפל הוא ביד יוסף היה יוסף זורק עליו פטומות.