A dung beetle cuts a ball from a pat, rolls it backwards with its hind legs, buries it, and lays an egg inside. Weeks later a beetle emerges from the ball. To an Egyptian observer that is two facts: something round is moved across the ground by an unseen effort, and life comes out of matter with no visible parent.
Both were used. Khepri is the god of the morning sun, shown as a beetle or as a man with a beetle for a head, and his name is formed on the verb kheper, to come into being. The sun at dawn is the ball being pushed up over the horizon, and the sun's daily return is the same self-generation the beetle appeared to perform. Ra has three forms across the day and Khepri is the first of them.
The biology is wrong, which does not matter to the result. Beetles do not generate from dung; the egg is laid in it. The misreading is exactly the kind of careful, mistaken empiricism that produces durable religious images, and it produced one of the most durable anyone has made.
The name and the verb are worth noticing together. Egyptian did not need a separate word for what the beetle does and what existence does. The scarab is not a symbol of becoming; it is the hieroglyph that writes it.