Pūriri Moth

Pūriri Moth – New Zealand’s largest moth

Aenetus virescens – Pūriri Moths are endemic to New Zealand, found only in the North Island.

Puriri moths in the Tangihua Forest

All stages of the Pūriri Moth lifecycle can be seen in Northlands Tangihua Forest. If you look closely at Pūriri or Putputāwētā trees you may find evidence of the caterpillars tunnels and feeding areas or even a tunnel currently in use.

During the day the moths themselves can sometimes be found resting on trees and in the evening, when they are most active, they may be seen flying around near the Tangihua Lions Lodge or even inviting themselves inside to fly around the lights.

Pūriri Moth Description

Male Pūriri Moth resting on a tree trunk –

His forewings are white, unlike those of the female, and his hind wings are greener than those of the female. Puriri moths are usually green, but the intensity of colour and wing patterning is very variable which can include blue-green, yellow, red and even albino Pūriri Moths have been recorded.

The males have a wingspan of up to 100mm and the females are even larger, with a wing span of up to 150mm.

Puriri moth behaviour

Pūriri Moths are mainly active in the evening, flying around lights and the holes they have made in the Pūriri or Putputāwētā trees. Male moths are more likely to be seen by people as they tend to be attracted to artificial lights more than the females are.

The Pūriri Moth goes through six distinct stages in life:

1. Eggs,
2. Caterpillar litter stage,
3. Transfer phase caterpillars,
4. Tree phase caterpillars,
5. Pupation and moth emergence, and finally,
6. Adult moth

Eggs

After mating the female moth scatters up to 2,000 eggs over the forest floor. The eggs are round and pale yellow when first laid, turning black a few days later.

Caterpillar Litter Stage

12 to 14 days after being laid, litter phase caterpillars hatch from the eggs. They live on the underside of twigs and branches on the forest floor where they feed on fungi. They make tunnels into the thick fungi which they cover with their droppings. This stage lasts two to three months.

Transfer Phase Caterpillar

At the end of the Caterpillar Litter Stage they will moult and become darker as they change to the Transfer Phase Caterpillar. This is when they locate a suitable tree, climb the trunk and bore through the bark and into the wood.

They construct a distinct tunnel shaped like a number 7. See photo opposite. The top of the tunnel goes almost directly into the trunk or branch, sloping upwards just slightly. The tunnel then makes a sharp turn and descends vertically down, creating a safe spot for the caterpillar to rest.

Tree Phase Caterpillars

At the end of the Transfer Phase the caterpillar moults again, turning into the paler Tree Phase Caterpillar. This caterpillar is a delicate, transparent, purplish-pink with a hardened dark-brown head capsule. It grazes on the cambium, the thin layer of cells that the tree develops to regrow its corky outer layer where it has been damaged by the caterpillars tunnelling. See photo opposite

These images show a Pūriri caterpillars’ home in a Putputāwētā tree

To protect itself the caterpillar builds a web over the hole and the area it grazes. see photo opposite. Some refuse and excrement (frass) is used to construct the web and the rest is ejected through a hole at the bottom of the web covering.

As the caterpillar matures it grows larger, up to 100mm long and 15mm in diameter. To accommodate for this growth it enlarges its tunnel, making it wider and longer. Once abandoned these tunnels are often taken over by Weta who make the most of a pre-constructed home.

The caterpillar remains in this stage for an average of two years for males and three years for females, but this interval can be as short as eight months or as long as five years.

Pupation and Moth Emergence

Once the caterpillar has reached full size it removes pieces of the web protecting it, either by making many small holes or removing the entire central portion of the web.

The caterpillar then blocks the top of the vertical burrow with a fibrous disc and transforms into a pupa, something similar to the chrysalis that Monarch Caterpillars form before turning into butterflies.

New pupae can be found between March and November. Pupa that form in October and November develop quicker than those formed earlier in the year but the average duration of this stage is 151 days for males and 173 days for females.

When the moth is ready to emerge the pupa wriggles up the tunnel, pushes up the disc and protrudes through the protective web. The climb up the tunnel is helped by 12 horny ridges, armed with hooklets, on the upper side of the abdomen and five similar ridges on the underside. Once at the exit, the skin of the pupa splits open, revealing a fully formed Pūriri Moth. Adult

Pūriri Moths emerge as moths at any time of the year, although the peak times are October to December with a second, minor peak in March. Pūriri Moths cannot eat as they have no mouths and live for only around 48 hours. During this short time the male and female moths find each other and mate, starting the cycle all over again.

Puriri Moth Distribution and Habitat

Pūriri Moths need areas with plenty of dead wood to provide the fungi the caterpillars need in their first stage of life. In later stages they need Pūriri or Putputāwētā trees to form a home and provide cambium for food.

Puriri moth Forest Role

Abandoned Pūriri Moth tunnels provide ideal homes for Weta. The name of the Putputāwētā trees, a favourite of the Pūriri Moth caterpillars, translates to ‘many weta’ due to the often numerous amounts of weta found living in Pūriri Moth tunnels in these trees. The adult moths make a tasty snack for Morepork s and bats and Kaka have been seen tearing at the wood of trees to get to the caterpillars in their tunnels.

Threats and Conservation Plan

An extensive study into Pūriri Moths found that there are three types of fungi and one bacterium that can harm the caterpillars and pupa. One fungi kills the caterpillar and covers the feeding area, one kills the pupae and one has the ability to kill both.

Possums and cats will eat the adult Pūriri Moths when given a chance but the biggest threat to Pūriri Moths is the destruction of the habitats they need to be able to complete their lifecycle.

The Tangihua forest block is managed by the Department of Conservation (DOC). They currently do not have the funding available to put in place the strategies needed to eradicate pests and protect the forest.

The Tangihua Lions Lodge has set up the following programs that you can be a part of;

Tangihua Community Pest Control Area: Targeting pests on farm land with local farmers and the Northland Regional Council

Conservation on DOC Land: Tangihua Lions Lodge Conservation and Education project

Conservation Education: Creating a high quality, accessible educational center surrounded by a fully functional ecosystem for schools and any one else who may choose to use the facility.

Volunteers Options : How you can help protect our native bush.

References

This article was written by Rachael Mannion

It is very apparent that specific information has been shared online between many organisations. Attributing to the initial source is impossible. As much as possible we have used our own photo’s and the following websites have been used as sources for our information;

• Te Ara The Encyclopaedia of New Zealand,
• Wikipedia,
• DOC website, and
• T.E.R:R.A.I.N Taranaki Educational Resource: Research Analysis and Information Network.