Large white

The female Cabbage white butterfly lays batches of 20 to 100 yellow eggs on plants in the brassica family and can be a pest on food crops. They seem to have a preference for cultivated varieties of Brassica oleracea such as cabbage and brussel sprouts. The caterpillars are yellowish green with yellow lines and black spots and feed in groups in plain view on the leaf surface. They gain protection from predators by possessing distasteful chemicals.

Protection
Attacks are worst during hot, dry summers, but the risk period is any time from April to October. Inspect the underside of leaves for patches of yellow eggs, if found, crush the eggs. Chemical sprays can be used, but to prevent their need cover your plants with a fine netting such as enviromesh or voile net curtain.