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Last week, Glen Wylie, of Spiderman pest control, was called to a South Hill address after a single redback spider was discovered by the property's owner, in a drain sump at the end of a driveway.
Mr Wylie, who has worked as a pest controller in Oamaru for 18 years and 30 years in total, said his investigations confirmed the spider was a redback, not a katipo, which had similar markings and was more common.
It was the first time he had come across a redback in North Otago.
"The guy that's found it has gone to clean the sump and it was just there in the middle. I went to check it out and the web was definitely that style that a redback would have.
"You do get quite a lot of spiders that are similar. They are very common and in exactly the same family as the katipo and the redback spider."
The discovery of the spider was probably "isolated" and did not mean there was a significant population in Oamaru.
He had simple advice for anyone who came across a redback.
"Kill it. They do bite, but it's more worrying for the frail or a child. That could be a wee bit worrying."
According to the Ministry of Health, redbacks would bite only when disturbed or trapped in clothing. A bite felt like a pinprick, and often resulted in localised redness, pain and sweating.
In some instances, pain might spread to the stomach and be accompanied by aches in muscles and joints, nausea, vomiting and increased heart rate and blood pressure.
The redback has been established in New Zealand since the 1980s and arrived initially in cargo from Australia. Small populations have been reported in Central Otago and Twizel, as well as in the North Island.
A Ministry for Primary Industries spokesman said sightings of redbacks did not need to be reported, but people were encouraged to contact the ministry if they discovered a spider they could not identify.