Cabbage white butterfly eggs. Coloured scanning electron micrograph (SEM) of eggs of the cabbage white butterfly (Pieris brassicae). The sculpted egg shells are made of a protein called chorionin and have aeropyles (breathing pores) that allow air to flow to the developing embryo. 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. Magnification: x100 when printed at 10 centimetres wide.