Thirteen flies become tasty snacks in this clever reverse counting book about subtraction, predators, and prey. Thirteen flies become tasty snacks in this clever reverse counting book about subtraction, predators, and prey. Science meets subtraction in this fresh and funny STEM picture book with plenty of ewww factor to please young readers. A swarm of thirteen flies buzzes along, losing one member to each predator along the way. Whether the unfortunate insects are zapped or wrapped, liquefied or zombified, the science is real--and hilariously gross. Includes a guide to eating bugs, complete with nutritional information for a single serving of flies.