The noble false widow spider has been sighted in Christchurch and Nelson after first being seen in Wellington last December.
Massey University evolutionary ecologist Prof Steven Trewick said the spider had now established itself in New Zealand.
He said the spider was not aggressive, but might bite in self-defence.
Pest Management Association of New Zealand executive councillor Vicki Smith is yet to encountered the spider in the South Island.
However, if it made its way further south, the region was well equipped to deal with it, she said.
"It’d be easy. It’s only like dealing with the white-tails."
Ms Smith pointed to another invasive species that appears to be making its way south, which could soon pop up in Dunedin.
Although there had not been any reports of the Argentine ant south of Timaru, it was on its way, Ms Smith warned.
Prof Trewick said bites from the noble false widow spider would result in mild symptoms such as swelling, redness and pain.
However, some had been linked to more serious effects, including tissue necrosis, nausea, hypotension, impaired mobility and secondary bacterial infections that may be resistant to standard antibiotics.
"It appears to be thriving in urban environments, particularly around gardens and outdoor furniture," Prof Trewick said.
"It is most often found under plant pots, tarpaulin and in fence crevices, while males are seen at night on exterior walls or the ground."
Although considered less dangerous than black widows, the venom of the noble false widow (Steatoda nobilis) contained similar toxins.
"Particularly concerning is its association with antibiotic-resistant bacteria. Infections resulting from bites don’t always respond to treatment, and that’s a significant medical concern," Prof Trewick said.
Originally from the Canary Islands and Madeira, the spider has become well established in Europe, North and South America and now New Zealand.
While the full impact of this spider on native wildlife was yet to be fully understood, its arrival reflected broader global patterns, Prof Trewick said.
"This is part of a wider pattern of biodiversity loss and rapid environmental change. Invasive species like this one highlight how globalisation and climate shifts are reshaping our ecosystems, often at the expense of native wildlife."
Suspected sightings of this spider can be uploaded to iNaturalist NZ to help researchers record the extent of the invasion.
