This morning's capture will push back the reopening of the troubled Countdown Dunedin South store another day - to Sunday.
The supermarket has now been closed for two weeks and 23 rats caught after staff raised concerns about a rodent problem.
Woolworths director of stores Jason Stockhill said as part of intensive pest-control work the supermarket walls had been investigated.
"This morning, we removed wall cladding in the store and uncovered evidence of old rat nests - but no signs of live nests," he said in a statement.
The news comes as the Ministry for Primary Industries says it will be keeping a close eye on Countdown Dunedin South even after it reopens.
Mr Stockhill said staff had been given updated food safety procedure training and managers had visited stores nationwide.
"We are making progress on reopening Countdown Dunedin South and thank our customers and team for their ongoing patience.
"It’s important that both ourselves and MPI are confident before we reopen to the community."
He apologised to customers for the ongoing disruption.
New Zealand Food Safety deputy director-general Vincent Arbuckle said yesterday when the supermarket reopened there would need to be "increased vigilance" at the supermarket to ensure pest control measures continued to be effective."
This would include ongoing monitoring by food compliance officers and daily updates on rat numbers.
Rats could enter supermarkets from time to time, but stores did not need to close each time as long as they were dealt with promptly and in a manner that minimised food safety risk, he said.
