Brian Patrick, Central Stories Museum director, of Alexandra, said the spiders are spread over an area that includes Alexandra, Bannockburn, Wanaka, Hawea and down to Te Anau.
"They are not uncommon. We get a few brought in [to the museum] every year. We've had two so far this year," he said.
He was commenting on the latest findings by AgResearch scientist and spider authority Dr Cor Vink and fellow scientist Dr Craig Phillips in an international journal, Biological Invasions.
Mr Patrick said the spiders seem to like the Central Otago climate, possibly because the hot summers are similar to summers in Australia.
"They originally came in on [shipping] containers and it didn't take them long to become established."
Dr Vink said the Australian redback was first found in the South Island near Wanaka, at the base of Mt Roy, in the early 1980s.
In the early 1990s, it was found at Bannockburn and Alexandra.
"The populations in those areas seem to be stable. They are definitely there, because I've found them myself. They are not easy to find, but I know where to look. In Alexandra, you can find them in among the rocks and thyme under the clock on the hill. They've also been found in Letts Gully."
Although extremely painful, a redback bite is unlikely to be fatal, Dr Vink said.
"There have been supposed reports of deaths in Australia but there is now an anti-venom available.
"Often, people don't feel the bite. It's only about half an hour later, when they start to feel extreme pain, they realise they might have been bitten. Unfortunately, it doesn't respond to pain medication," he said.
Anyone who thinks they have been bitten by a redback should seek medical treatment and, if possible, catch the spider for identification, he said.
The remains of chafer beetles had been found in the webs of redback spiders, Dr Vink said.
However, these were more likely to be the Alexandra chafer beetle rather than the endangered Cromwell species.
