Karnal is a city of over 1 million people, about 76 miles north of Delhi. And they have a problem with rats. Perhaps not as severe as that faced by the people of Hamelin in medieval times:
Rats!But they were certainly a problem to the police, chewing up vital papers and gunny bags. About a month ago, someone suggested introducing domesticated white mice, which they went and purchased from a laboratory supplier.
They fought the dogs and killed the cats,
And bit the babies in the cradles,
And ate the cheeses out of the vats,
And licked the soup from the cooks’ own ladles! 
Within a month, the black rats had disappeared, and now they are planning to introduce white mice to other police stations in the area.
A local zoologist said that the white mice have genetically more dominant traits than the black ones and eventually they come out on top in the competition.
In Britain and other chilly countries, the Black Rat (Rattus rattus), which carried the bubonic plague, has been largely driven out by the Brown Rat (Rattus norvegicus), which doesn’t. For this reason, my father used to refer to the latter as “The Gentleman who Saved Europe”.
And Hamelin again has a rat problem.
source: Times of India
 The Pied Piper of Hamelin by Robert Browning.