Uninvited guests coming to a farm near you.
Nine out of 10 producers say vermin problems have worsened over a winter which, despite today's expected snow, has been one of the mildest on record.
Experts claim the trend is set to continue as global warming creates ideal conditions for rats to breed and spread.
Steve Jasper, of Alpha Pest Control, Llangollen, said: "Most farmers act quickly to deal with the problem and we've certainly seen a big rise in call-outs this winter."
Last month the National Pest Technicians Association reported that, in Wales alone, brown rat infestations rose 14% over 12 months and house mice 25%.
Rodenticide manufacturer Sorex says livestock farmers are spending more on vermin control to cope with rising farm assurance demands
It found more than 90% of producers have problems with rats and 65% with mice.
Sorex technician Sharon Hughes said the mild autumn and winter had seen rats multiple rapidly on many holdings.
She said: "The onset of colder weather drives large numbers of rats into farmyards for warmth, shelter and sustenance."
For a free 12-page guide to rodent control, ring Sorex's national Think Rat Hotline on 0151 4207151.