Rats, like rabbits, are proverbially prolific. One of the few things, however, that can get their numbers down is a good cold winter, since apparently it makes them less enthusiastic breeders.
Prior to about 1450, Europe enjoyed several centuries of very benign conditions when the climate was significantly warmer than it is now, and this may well have contributed to Hamelin's problem with these loathsome creatures. The story has been nicely documented:
The Rats! They fought the dogs, they killed the cats, And bit the babies in the cradles, And ate the cheese out of the vats And licked the soup from the cooks' own ladles.
According to legend, the solution to the problem arrived in town in the shape of a mysterious piper in a multi-coloured suit who offered to rid it of vermin for a certain sum - an offer that was readily accepted by the townspeople.
The piper fulfilled his contract by piping the rats into the River Weser, where they drowned.
With their problems solved, the good citizens of Hamelin decided to welsh upon the deal, and as we know, the piper took his singular revenge. Some time later - the legend has it that it was 715 years ago today, on July 22nd, 1284 - the piper reappeared and played his pipe again. This time all the town's children followed him:
All the little boys and girls, With rosy cheeks and flaxen curls, And sparkling eyes, and teeth like pearls, Tripping and skipping ran merrily after The wonderful music with shouting and laughter.
The piper led them to a cave, into which all except one disappeared, never to be heard of any more.
Although accurate statistics are almost impossible to gather, there is anecdotal evidence that in various temperate regions of the world rats are thriving these days more then usual. Some zoologists see the recent succession of milder winters as an important contributory factor and have voiced the fear that if global temperatures continue with their present upward trend, the increase in the rat population may accelerate dramatically.
These climatic worries are exacerbated by the fact that the rodents' parasites that carry infections such as the sometimes fatal Lyme disease, also thrive in the warm, mild, moist conditions that might be a common feature of some future climates. At the very least, climatic change would affect the global distribution of Lyme disease and other ailments spread in similar ways.
We may need the Pied Piper once again - and this time we should pay him.