A larva (caterpillar) of a large white butterfly, Pieris brassicae, emerging from its egg. The picture, a scanning elelctron micrograph, shows a group of ova (below, ribbed) on a leaf of Pak choi, Brassica campestris. The larva has emerged by eating through the shell; the initial hole produced by a second larva is visible, bottom edge to left. Five simple eyes (ocelli) are visble on the left side of the larva's head, as small hemispherical bulges. Pieris brassicae is a serious pest of brassicas, such as cabbages, kale and brussel spouts, particularly in gardens. The larvae accumulate mustard oils from the leaves as they feed, and this deters many predators, although the parasitic wasp Cotesia glomeratus can kill as many as 20% of the population in some years. P. brassicae is a migratory species and a strong flier, known to cross hundreds of kilometres of open ocean. Mag x 100 at 10x8