They drop by night

Camels are called Daughters of the Night.

-The Life of Animals, Kamal al-Din al-Damiri (1341-1405)

Al-Damiri doesn’t explain the origin of this sobriquet, but since he immediately continues by saying they are also called Ba’īr, Round Dung Makers, I can only wonder if he meant that each pile of turds dropped by a night-couched camel reminded him of a big family of girls.