Tadpole's Promise by Jeanne Willis
Where the willow meets the water, a tadpole met a caterpillar. They gazed into each other's tiny eyes and fell in love. 'Promise me that you will never change', the caterpillar says. And foolishly, the tadpole promises. But as the seasons pass and he matures, his legs grow, and then his arms - and what happens to his beautiful rainbow friend? As he sits on his lily pad, digesting the butterfly he has just eaten, he little realises that now he will never know!