Usually when we hear Great White, we think of the Great White Shark which has a fearsome reputation. Recently a new Great White has appeared on land, and while it might look like a cute butterfly it has a fearsome reputation too!
Gardeners think of the Cabbage Butterfly (or Small White) as a pest, it seems that the Great White is even more destructive and is a danger to native plants as well as to crops.
It is their caterpillar that is destructive, eating up large amounts of leaves and making it hard for plants to grow. Each type of butterfly favours a different plant, and both the white butterflies like plants in the brassica family. This includes cabbages, broccoli and nasturtiums.
Great White Butterflies have been found in the Nelson Tasman region and will spread further if they aren't found and killed. On my last visit to Nelson I thought I'd do my bit and check out this nasturtium plant - its holey leaves showed it was clearly being eaten by caterpillars. I found caterpillars which are the same green as the stem of the plant, a great camouflage! They looked like Cabbage Butterfly (Small Whites) caterpillars, Ned has illustrated one in In the Garden on page 21. I checked DOCs Great White Butterfly fact sheet to make sure they don't have a similar caterpillar and saw that the Great White caterpillar has black spots and looks quite different.
Later I heard that this nasturtium had already been checked along with other plants in the garden by the Great White butterfly eradication team.
If you live in Nelson/Tasman you can help by looking for host plants, checking butterflies and caterpillars against the pictures in the fact sheet and following the advice from DOC.