When a female dung beetle finds a nice piece of dung, she digs a tunnel through it and down into the earth below. She then pulls small pieces of dung into the tunnel with her, which she makes into little balls.
Next, she lays one egg into each ball. This is so when the eggs hatch, each larva can feed on its ball of dung in peace.
If a male gets plenty of food early on he will grow big in size with horns to match. However, if a male larva gets little food, he will stay relatively small, either growing horns that are very short or not growing any horns at all.
In mating, females don't have a specific preference for either the big horned male of the smaller hornless males. About half the population of male dung beetles are big and horned, while about about half are small.