Other Whanganui women who do the same work include Trieste Neilson and Lou Nation.
She named "colonies" of cats near the Ab Fab florist shop, Pak'n Save, City College, Talbot St and Salisbury St.
A female cat can have three to four litters of kittens a year, and start breeding at four months. That means a group of five cats behind a shop can become 150 cats in just a year, Thomas said.
They cause problems by defecating, fighting and killing birds, and male cats also spray.
She would like the council to provide more cat traps and money to desex the cats that are caught, perhaps in a partnership with the SPCA.
The problem is "horrific", councillor Charlie Anderson said. He recalled seeing wild cats running across farmland too.
The council's proposed three cat limit per household will not touch the problem, Thomas said, but she agrees compulsory microchipping and desexing for pet cats is good.
The SPCA and the council's compliance team leader Warrick Zander have both said people are responsible for cats on their properties and in their care. If the cats are unwanted, the resident should check they are not someone's pet before having them humanely euthanised.
Stray and feral cats are not captured by the council's bylaw on kept animals, Whanganui mayor Hamish McDouall said. He suggested Thomas ask Horizons Regional Council for help.
Horizons' pest management plan does not include feral cats, but people with issues can contact its animal pest team for advice by calling 0508 800 800.
Committee chairwoman Helen Craig asked staff to bring a report about the cat problem to a future meeting.