A Portuguese millipede at Te Kopahou information centre Photo: RNZ/Mary Argue
Work to explore how to control an infestation of millipedes in Wellington is set to begin, with an expert advisory group due to meet on Thursday.
Residents in the capital's southern suburbs have said they're dealing with an explosion of Portuguese millipedes in their streets and houses in autumn.
In recent years locals have described waking to find hundreds of scaly black millipedes around their homes, discovering them in shoes, bags and even their beds.
At the entrance to Red Rocks on Wednesday there were dozens of dead millipedes on the ground around Te Kopahou information centre, with a few live ones crawling around.
A nearby resident confirmed the creature's numbers had dwindled to only "a handful around the area that would normally have dozens".
Advisory group member entomology professor Phil Lester said the millipedes are most apparent in autumn, when the adults emerge from the soil.
They are not visible at other times of the year as they are typically in the soil eating decaying plant material.
The outbreak prompted Wellington city councillor Nureddin Abdurahman to demand an urgent meeting to discuss how the district and regional councils could better monitor and contain the millipedes.
The Ministry for Primary Industries said because control options were limited, a Technical Advisory Group - including representatives from the Department of Conservation and regional and city councils - had been set up to investigate possible solutions.
If you've been affected by the millipedes contact Mary.Argue@rnz.co.nz
Portuguese millipedes. Photo: Supplied
According to the group's entomologist and an independent specialist in insect biological control, those solutions could include a tiny parasitic worm that kills the millipede from the inside out - like a "horror show".
Managing director of Bioforce Christopher Thompson said his company specialised in controlling insect species using other insects, mites and microbes.
He said the nematode Steinernema feltia, which is naturally present in New Zealand soil, could be an effective biocontrol agent against the Portuguese millipede when deployed in numbers.
"Once they've wiggled their way in through some holes and gaps in [the insects'] body, they're able to start reproducing.
"Eventually they'll get so numerous in there they'll explode out of the host - not something you want to watch just before having dinner."
Thompson said a millipede host could hold tens, or even hundreds, of thousands of nematodes before it burst.
"It is a bit of a horror show to be fair, but it's nature."
He said insects were a particular target of the worm, so it was possible that if used against the millipede population in Wellington, it would jump to other species in the garden - although he believed the weta would be fairly safe.
Larger life forms - such as humans, frogs, skinks, and birds - were unsuitable hosts, he said.
Thompson said pitting the worm against the millipedes was as simple as ordering the parasite in the post, mixing it with water in a watering can, and pouring it around the property.
He said any control efforts would be better sooner rather than later before the "you problem" became a nation-wide problem.
Entomology professor Phil Lester. Photo:
Advisory Group member entomology professor Phil Lester agreed, telling RNZ it would be great if the millipede population plaguing south coast residents could be nipped in the bud.
He said the millipedes was already widespread in Australia and had been in New Zealand for about 20 years.
"So, it seems like they would love the New Zealand climate quite a lot and would have the ability to spread widely if we didn't get on top of it now."
Lester said the goal of the Technical Advisory Group was to investigate control tools for problematic pest species, including what could be done by the public.
He suspected Thursday's meeting would be the first of many and would set the scene for current control options, as well as sparking further research into other methods.
Lester said an Australian nematode species had proven to be an effective biological control against the millipedes and it would be great if something similar could be done for Wellingtonians.
"If we can encourage that... that would be awesome [and] alleviate some stress for many of the residents."
Biosecurity New Zealand manager of pest management Dr Cath Duthie said the Portuguese millipede was first detected at Seaview, Lower Hutt, in 2021 but it was apparent it had been in the region for at least two decades.
She said it was primarily a "nuisance pest" where it had been introduced.
"As management options are limited, a Technical Advisory Group has been formed... to explore potential control solutions for the species and recommend other control methods for existing identified populations."
Duthie said in the meantime, the regional council had information about management options for the Portuguese millipede on its website.
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