It has been assumed that rats spotted in New Zealand supermarkets were Norway rats but could roof rats have been the culprits?
The importance of maintaining a rodent-free commercial premises, especially if it is a food handling establishment, cannot be underestimated. Apart from health and safety issues, reputational damage can be significant. The recent rodent issues at the Woolworths store in Dunedin, New Zealand, is a case in point.
Back in October 2023, rats were photographed in the refrigerators of the Woolworths store. It didn’t need to be much of a “slow news day” for the photos to go viral. As a result, over the following weeks, photos and videos of a variety of pest issues in a number of different supermarkets across the country came to light – mice in the deli at a Christchurch store, pigeons on shelves in an Auckland store.
viral (rat is reflected in the mirror)
Of course, Woolworths and its pest management protocols came under close scrutiny, with the Ministry for Primary Industries (MPI) NZ Food Safety Division launching an investigation.
Whilst an occasional rodent sighting can be put down to the challenges of rodent management – 100% exclusion of rodents from a building as big as a supermarket, filled with a large amount of potential food is nigh on impossible – repeated sightings and the appearance of rodents during the day indicate a more significant issue.
Following the original sighting at the Dunedin store in October, several more rats were captured. Then, following a period of intense pest management activity, it was thought that the problem was under control by the end of January 2024. Unfortunately, a week or so later several more rats were captured, causing the Dunedin store to close for three weeks. The management plan was working on the assumption that the rodents were entering the building from the outside, but during the closedown, evidence pointed to rats nesting in the walls.
Since the store has been re-opened, a small number of rats have been captured, which management claim demonstrated the pest management programs were working as expected. Investigations into the rodent problem are continuing and it is hoped that learnings can be shared at a later date.
It has been suggested that rats at the Dunedin store may have been roof rats (Rattus rattus, main picture above). If this is the case, it follows a developing trend in New Zealand. Previously, the general belief has been that the Norway rat (Rattus norwegicus) is the most common rat in New Zealand, but ongoing market research by the Pest Management Association of New Zealand (PMANZ) suggests that this may not be the case.
“Our ongoing study with PMANZ members indicates mice are the number one pest rodent, followed by roof rats, followed by the Norway rat,” said Gerwyn Jones, vice president of PMANZ. (Similarly, in Australia, the roof rat is more common than the Norway rat.)
Whilst it is unclear whether this was one of the contributing factors in the Dunedin situation, Mr Jones stressed the need to carry out a thorough inspection prior to putting a rodent management plan in place to identify the species present, as well as identifying areas of activity, building entry points and nesting sites.
“By default, many rodent management plans for commercial accounts have traditionally included internal and external bait stations at ground level. This is a fairly sound strategy when the dominant rodents are house mice and Norway rats, but if the pest rodent in question is the roof rat, a different strategy is required,” said Mr Jones.
