They should use BSFL instead. The grubs move a lot faster and will entertain the kids more. I hope they do this (worm racing) in the shade. Six minutes under the sun will harm the worms.

This is done in a covered pavilion. The article states:

The truth is, unlike horse racing, or even the pig racing that attracts standing-room-only crowds, the worm races aren�t really about racing. They're about education and agriculture, the sometimes overlooked parts of the fair.

The children learn that Red Wigglers are vermicomposters. They live on the fair year round, eating scraps from the kitchen that never make it to the public. Their droppings become rich fertilizer that the staff can use throughout the year.