I think this is not a problem with the rats growing in size but the stupidity of people who leave plenty of food around for them to eat. Rats reproduce quicker than many species. Where there is plenty of food and they still get excercise (eg from field to shed where food is) they will get bigger and bigger and their bodies will adapt. Same thing with mice.. except most people deal with those. Quite frankly I have no issue with mice other than they're noisy little critters when scampering along the ceiling at night. Oh and they got under the sink to where SWMBO keeps the "bag for life" bags and chewed them to bits (also dragging a few bags up the pipe box into the loft )
I need a new signature... i'm bored of the old one!