the scientific name for the swift ("apus") comes from the ancient greek word απους, "apous" which means "without feet". this is because swifts have very small, weak feet. swifts use their feet to hold on to vertical places (for example, the wall of a house, or a cliff). swifts do not want to land on the ground. it is often thought that if they land on ground, they cannot fly up again, but that is not true. they can take off but with difficulty.