Great white butterflies lay their eggs on the leaves of plants that contain mustard oil. The caterpillars feed on the leaves and use the mustard oil to produce their own chemical compounds that give them an unpleasant flavour. This flavour together with their distinctive coloration gives them some protection from potential predators.
Mustard oils are found in many plants in the Mustard family (Brassicaceae) but also in some plants in other families too. The mustard family includes many common vegetables, some important crops, some common weeds and 79 species of New Zealand native cresses.
Below are some of the plants favoured by the great white butterfly on which its caterpillars and eggs can be found. Some of these plants may be growing wild in your garden without you even knowing.
New Zealand Weeds - Massey University website