Cabbage white butterfly eggs. Close-up the underside of a leaf with attached eggs of the cabbage white butterfly (Pieris brassicae). This is a pak choi leaf. The eggs are on the point of hatching, with the dark head of the larva (caterpillar) visible through the egg case. These eggs are laid in batches of up to 100 to 150 on the underside of brassica plant leaves, hatching after about 10 days. Once hatched, the caterpillars feed on the leaves, growing in size until they are ready to metamorphose into the butterfly stage that will lay eggs and start the life cycle anew.