Scientists investigate venomous spider 'hotspots'

Researchers are investigating "hotspots" of a venomous spider throughout the country this summer.

The invasive noble false widow spider was first spotted in Porirua last year with further sightings in Christchurch, Nelson, Waikato and Northland.

It's not an aggressive spider, but it bites in defence and the toxins in its venom cause swelling, redness and pain.

In July, Massey University ecology professor Steven Trewick put the call out for suspected sightings to understand how widespread they are.

"We thought that with the level of interest in this spider, we would hear a bit more from people, perhaps slightly panicky kind of responses saying they found some spiders," he said.

"And in fact it's been surprisingly quiet."

That could be because people have not recognised it, he said.

"The other possibility is that in fact, this new invasive species is not as widespread as ... early indications suggested.

"So it could be that it is very locally abundant, possibly in a number of places around the country ... and hasn't spread sort of uniformly across the landscape."

This summer, Massey researchers will search the "hotspots" where they've already been found, beginning in Porirua.

They'll gradually move away from urban areas - metre by metre - to see if the spiders are still present as they head into grass, shrub and bush.

"It could be that they're hotspots because that's just where we've paid attention, or they're real hotspots because there are relatively high densities of these spiders just in those places," Trewick said.

Their locations could also be determined by the wind, he said.

"When the hatchlings pop out of their little bundle of eggs, this little sort of cocoon, very, very tiny, the first thing that they do is let out a little strand of silk ... and that catches the wind and is enough to lift them off and take them away.

"Many of them, of course, will land up somewhere useless, but some might find just a nice little spot to make their first web."

Researchers will also do population genetic work to understand how many spiders arrived in New Zealand, and which country they came from.

PhD students in the British Isles, Europe and Chile are undertaking similar efforts, Trewick said.

"It becomes a really interesting multinational effort dealing with, sort of a common problem."

Biologists wanted to know whether the spider was moving into native environments, and interacting with other native spiders and animals, he said.

"If that happened, then that would be a bigger ... biodiversity conservation issue."

What to look out for - and where

The noble false widow is a pale reddish colour with distinctive white markings on the abdomen, "the big blobby part of the body," said Trewick.

They have a large spherical abdomen, smaller "front end" and long, naked legs, Trewick said.

"Sort of a classic cartoon spider, not your hairy tarantula-y kind of spider at all," he said.

The spiders are about a centimetre long, and the legs are another couple of centimetres, said Trewick.

They've been found around people's homes, under pot plants, tarpaulin and in fence crevices.

The spiders are most active at night, and they're speedy, so can disappear quickly once they've been disturbed, said Trewick.

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