25 percent of brown rats in the Netherlands are resistant to rat poison. Even if they eat it, they do not die afterwards, or die only after a long time.
Scientists of the Wageningen University made a nationwide call to send rat droppings in August. Of the 361 packages they received from across the country, 169 samples were suitable for analysis.
NOS.nl reported that in parts of Twente and de Achterhoek, in the east of the country, people found droppings only from poison-resistant rats.