Great white butterfly hunt steps up

Date:  27 February 2013

The Department of Conservation is calling on the public to help kill great white butterflies as efforts ramp up to eradicate the pest from Nelson Tasman.

The request comes in anticipation of a spike in great white butterfly numbers as they emerge from pupae in the autumn.

“’Kill the butterflies please’, is what we’re saying now,” says DOC Motueka Area Manager, Martin Rodd.

“It sounds harsh but it’s crucial to stopping their spread.  We need to destroy the butterflies before they lay their eggs.”

Butterfly nets or tennis and badminton racquets can be used to catch the butterflies, which should then be squashed. People should not be concerned about killing the smaller but similar looking white butterfly by mistake, as this is also a garden pest. 

“We still want people to report findings of eggs and caterpillars to the Ministry for Primary Industries (MPI) hotline 0800 80 99 66 but now we really need people to catch and kill the butterflies too if we are going to have a good chance of eradicating it.” 

The next month or so will be a critical time in the great white butterfly eradication operation, which has been progressing well, says Rodd. 

“We’ve had great support so far with dozens of people ringing in each week over the summer, many with positive identifications of caterpillars and eggs, which have since been destroyed.” 

Work to remove uncontrolled nasturtium plants, a breeding favourite with the butterfly, has also been underway. Nelson residents have been asked to report patches of wild, uncared for nasturtium to DOC’s Nelson office, ph (03) 546 9335 or email motueka@doc.govt.nz. 

A single dead caterpillar was found in Upper Moutere two weeks ago, 20 km beyond the known range of the great white butterfly. However, a thorough search in the surrounding area revealed no further signs of the pest.

“This find reinforces why it’s so important for residents in Tasman, as well as Nelson, to keep a look out for eggs, caterpillars and butterflies,” says Rodd.   

The tiny, yellow eggs and caterpillars are found in clusters on host plants particularly nasturtium, honesty and brassica vegetables such as broccoli and cabbages. The caterpillars are very small when young and in later stages they are speckled black and greyish-green with three yellow lines along their bodies. 

DOC is leading a multi-agency effort with Vegetables New Zealand, MPI, Tasman District Council and Nelson City Council to eradicate the butterfly species to prevent it becoming a major pest in New Zealand. First found in Nelson City, the great white butterfly poses a major threat to commercial and home brassica crops and to native cresses. It is known in some countries as the large white butterfly.

Great white butterfly identification information

The adult great white butterfly looks similar to the small white butterfly, though about twice the size, and it is easier to tell the difference between them by their caterpillars and eggs. The great white’s caterpillars and eggs are mostly in clusters whereas those of the small butterfly caterpillar are mostly found singly. 

The great white butterfly caterpillar’s appearance changes through five growth stages. When very young, the tiny caterpillars are yellowish with a shiny black head. Then dark spots begin to appear on the body. In later stages, it is speckled greyish-green and black and has three yellow lines along its body. Larger caterpillars have lots of pale hairs and, when fully grown, are 50 mm long. 

In contrast, the small white butterfly caterpillar is uniformly green with a faint yellow line along the top of its body and is about 30 mm long when fully grown.

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