The puriri moth is our resident stealth bomber, flying silently under the forest canopy on a mission to drop its cargo: eggs, not explosives, even if for some of the trees there will be damaging consequences.
This generously-sized insect, endemic to the North Island, is a somewhat elusive critter. Most of its early life, in caterpillar form, is spent burrowed deep within a host tree trunk. Once it emerges in its splendid final form as Aotearoa’s largest, most brilliantly-coloured moth, it lives a mere 48 hours. Provided it doesn’t end up as dinner for a hungry ruru or robin.
Those who claim to have seen the puriri moth (Aenetus virescens) up close can vouch that it is quite a sight. Females are particularly eye-catching, with a wingspan of 15cm and distinctive bottle-green and brown patterned forewings, and pinkish underwings. The male is slightly smaller, with white-patterned wings. In the light, the moth’s brilliant green colouring creates an almost transparent look, hence its nickname “the ghost moth”. Though, some moths stand out from the crowd, with turquoise, brick red and even albino colourations.
The moths are typically nocturnal forest dwellers. They are most likely to be spotted on warm spring evenings, not far from areas of native bush (several have been seen at Mount Bruce near the Pukaka Wildlife Reserve, for example). In the past, the males could be found swarming around lights in populated areas bordering forests; however, now that tracts of forest have been cleared, this is less common.
The puriri moth’s enigmatic existence begins with the adult female of the species – whose foremost mission in her brief life is to give the next generation a good start. To achieve this, she flies over as wide an area as she can reach, scattering up to 2,000 eggs throughout the forest, near suitable host trees.
These eggs hatch into caterpillars, which spend their early days eating the soft underside of fungi attached to the side of trees or dead branches on the forest floor. After a couple of months the caterpillar is ready for more substantial fare and more solid surroundings. It makes its way to a tree trunk where it cuts through the bark, and begins work on the distinctive vertical tunnel which will house it for most of its life.
The puriri moth caterpillar makes its home inside about 60 to 70 tree species, both native and introduced – though its preferred lodging is the wood of the maire and puriri trees (after which it is named). Another favourite port of call is the tree known as marbleleaf or putaputawētā – so named for the weta that shelter in the old holes vacated by puriri moth larva.
Once settled inside the tree, the caterpillar doesn’t venture far – emerging only at night to graze the rich tissue under the bark, leaving a scar where the tree tries to repair the damage. The caterpillar tries to disguise its activities by constructing a screen of chewed bark and silk to cover its feeding ground – but not always successfully, as kaka can find it and tear at the tree to get at the succulent grub inside. The larvae were also sought after by Māori, who used them as eel bait (naming them “pepetuna”), after flushing them out of their tunnels with water.
The caterpillar can remain in the tree for up to five years – though males mature more quickly, and can pupate within eight months. Once the larva reaches approximately 10cm in length, it forms a chrysalis at its tunnel’s entrance, and begins metamorphosis – eventually emerging as the magnificent, but short-lived green moth.
Once the adult moth crawls from the tree, they have just enough time to mate and lay their eggs – and so, the process begins again. The moths don’t even have mouthparts; as they gain all the resources they need as caterpillars, feeding in the two or three days they live is not necessary.
How the males and female moths find each other is not known. Chances are, pheromones play a big part.
So elusory is the puriri moth that photos of a moth hatching from a putaputawētā tree, captured on a Waikanae reserve back in 2009, were believed to be a world first. The photos were run in The Dominion Post, and caught the attention of a moth expert from the Buffalo Museum of Science in the US.
A strange little life for such a spectacular creature, but a fascinating one nonetheless!