Historic millipede outbreak sparks fresh research

There are several reports of millipede infestations in Hawke's Bay, Tauranga and in the Wellington suburb of Kilbirnie from more than 75 years ago.

Photo: National Library of New Zealand

The black, wormlike creature - about two inches long with hundreds of "hairlike" legs - crawls up walls, drops into food and causes general "havoc" in the home.

Residents say they're alarmed but also annoyed by increasing numbers of the "sinister-looking" millipede invading their homes in spring and autumn.

It could be a report from Wellingtonians who, over the past couple of years, have described hordes of black Portuguese millipedes in and around their south coast homes - showing up in bags and even beds.

But these alarmed residents are in Napier, and in the year 1949.

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The article in the Hawke's Bay Herald-Tribune is one of several reports of millipede infestations in Hawke's Bay, Tauranga and in the Wellington suburb of Kilbirnie from more than 75 years ago.

The historic accounts have sparked a fresh line of inquiry for those investigating Portuguese millipede control in Wellington, with researchers claiming it could yet offer hope for residents.

Potato slices and poison

"All you can do is sit and watch the invasion."

The quote from a Kilbirnie resident appears in a 1947 April edition of the Evening Post, where they describe millipedes crawling up the walls as "flies' play", compared with the thousands in the garden.

"Every handful of soil yields its quota. We wish we knew how to rid ourselves of them."

Another article from the same time, but in the Bay Of Plenty Times discusses possible eradication methods for millipedes affecting residents in Tauranga.

A mixture of bran, Paris Green (a highly toxic copper-arsenic insecticide), molassases and water is recommended to be dusted under houses and along walls - "wherever millipedes were causing trouble".

On the morning of March 16, 1949, black millipedes are seen in Napier "near the back premises of a town hotel crawling about the yard and clinging to walls".

The Hawke's Bay Herald-Tribune reports the hotel staff have experienced "great difficulty" trying to keep the creatures out of the building.

A Portuguese millipede at Te Kopahou information centre.

Photo: RNZ/Mary Argue

Potato slices "impregnated with Paris Green" are suggested as a possible control method.

In recent years, Wellingtonians on the south coast have also pursued methods to quash a booming millipede population.

According to the Ministry for Primary Industries (MPI), the invasive Portuguese millipede has been in the Wellington region for more than 20 years. It is considered a nuisance species rather than a pest and is therefore not subject to official pest control measures.

In April last year, Chris Picking told RNZ he'd found the millipedes in every nook and cranny of his home on the south coast.

"We've had them in the lounge, in the bed, we've had them crawling on the dog, hanging from the walls and the ceiling.

"I've had one on me in the bed [and] I've woken up and it's been on my face. Anywhere you can think, I've seen them."

Millipede numbers surged again in autumn this year, with an Ōwhiro Bay resident telling RNZ in March there was "less concrete more millipedes" outside the house.

"They're just pouring out of the soil - [it's] probably got to do with the [recent] rainfall. It's essentially like a millipede graveyard right now."

The infestation of Portuguese millipedes has triggered pleas to the authorities for help, public meetings, and the establishment of an advisory group to investigate suppressing the insect's numbers.

Entomologist and Victoria University professor Phil Lester, who has been leading the research, last month broke the news that a parasitic nematode was ineffective at killing the nematode.

Some Ōwhiro Bay residents had been spraying the microscopic worm, Steinernema feltia - which naturally occurs in the soil - around their homes in the hope it would suppress millipede numbers, but Lester said trials showed it would not work as a biocontrol agent.

However, he said the collection of historic articles that recently landed in his inbox has sparked a new research project.

'Boom and bust' cycle piques interest

The similarity between accounts of millipede infestations seven decades ago and present day Wellington, is striking, Lester said.

"These are black millipedes that are crawling up walls and they're seen twice a year, in spring and in autumn and they're everywhere and they're driving the residents absolutely crazy. We haven't seen any of the pictures, but they sound an awful lot like Portuguese millipedes."

The "nasty pesticides" used on the millipedes all those years ago, could have reduced their numbers, Lester said.

"But we do see in a bunch of other pest species like this, boom and bust cycles.

Potato slices "impregnated with Paris Green" are suggested as a possible control method.

Photo: National Library of New Zealand

"They suddenly boom and then they die away and they aren't a problem anymore. Unfortunately, we don't get in the newspapers, 'Hey, these things aren't a problem anymore.'

"So, we don't know precisely when they stopped being an issue for people. But certainly, nobody's complaining about them now."

Bay of Plenty and Hawke's Bay regional councils had no recent reports of millipede infestations in the area.

MPI said it did not track populations of Portuguese millipedes and could not confirm whether the historical reports referred to the species.

Lester said the mystery of why millipedes peaked and suddenly vanished was worth exploring.

"It's tempting for people like me who study parasites and pathogens to say ... all of a sudden a parasite or pathogen caught up with them and knocked back the populations. But that's just a hypothesis at this stage, we don't know for sure."

He said it could provide some hope for those plagued by millipedes in Wellington.

"If there's been a boom and a bust somewhere, why can't there be a boom and a bust here?"

The question is so compelling that it's become the prioity for one of Lester's research students who will head to Tauranga this summer to conduct fieldwork - with both Greater Wellington Regional Council and Wellington City Council contributing money to fund it.

Lester said it would be tricky, but the ideal scenario would be to find a population of Portuguese millipedes and identify pathogens or parasites in it that could be introduced in Wellington.

"We'd just love to know what the heck happened up there that caused this crash in populations. Why aren't they a problem anymore? And why are they a problem here, what's the difference?

"It's hard work to do but I think the residents in Ōwhiro Bay would be pleased if we could find that."

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