Wellington's rat problem is causing strife as rodents chew through dishwasher pipes, wires and ducting.
But a predator-free group says this is a sign eradication efforts are working.
The rats are destroying house infrastructure to maintain their teeth, says Wellington Pest Management managing director Darren Labrum.
He says business is up 30 percent since last year, and with more rats, he's seeing more damage.
- Increase in rats being caught by backyard trappers in Wellington
- Hordes of rats the size of cats infest Auckland suburb of Titirangi
"If they don't chew things their teeth will just keep growing, until they grow into their jaw and they die," he told Newshub on Thursday.
He says manmade products are really good for rat tooth maintenance.
"Obviously, they live amongst us so they're going to chew what's closest to them. Pipes, ducting, things like that are really good for their teeth."
Although there are certainly more rats than usual, Labrum says they are not the "monster" rats some say they are.
"They're not necessarily any bigger but there are more of them. We're not talking about super-rats, just well-fed rats in their prime size."
The boom in rodent population is due to the mega-mast, which caused higher forest seeding.
Labrum says there are things residents can do to protect their homes, such as blocking up holes.
"If you can poke your thumb through it, you can get a rodent in it," he told Newshub.
He also recommends securing compost bins, not leaving food out, and trimming back trees which allow roof access. But none of them are guarantees.
"That's why I own a business - because they can just get in anyway."
But Predator Free Wellington says the chewing is a good sign its eradication process is working. The group is aiming to make Miramar Peninsula pest-free by Christmas, and has installed more than 6000 traps and bait stations throughout the area.
A picture posted to the Predator Free Miramar Facebook page shows a bait station chewed to shreds by a "seriously hungry" rat.
"We have had a number of bait stations where rats have chewed through the plastic sides and internal components," said the group.
"This is a really positive indicator for us, we know the devices are installed in the right locations and the rats are coming in and getting comfortable with them."