IT IS 21 days to Christmas, and, if you are Icelandic, you know what that means. In a little more than a week's time, the Yuletide Lads will wake up. One by one, they will leave their cave in the mountains and stealthily slink towards your home, bent on mischief.

The first Lad, Stump, (also known as Sheep-Cot Clod) will stagger down on his peg-leg and make a beeline for the barn to wreak havoc with the sheep. Then, for the 12 days leading up to Christmas, he will be joined, one a day, by his 12 brothers. By 25 December, all 13 will have arrived, slammed doors, stolen food and done unspeakable things to the furniture. Then they will leave again, one by one, until 6 January, in the reverse order of their arrival.

Their homeland has a fittingly raw nature. The island originally boiled up in the rift between the European and American continental plates and, since then, the geothermic activity has produced earthquakes, volcanic eruptions and, less threateningly, geysers. And the Icelanders have tried to make the best of the drama. They harnessed the geothermic energy to heat and power the south of the island; they swim around the year in pools fed by hot springs; and the Althing, their parliament (one of the oldest in the world), used to meet at the cliffs that mark the continental divide.

Iceland was officially Christianised in AD1000, just 126 years after it was first colonised by Norse settlers, but, try as it might, Christianity never really erased the old Viking beliefs. They were too much a part of the landscape, literally. Many Icelanders still believe that elves live in the huge boulders of the lava fields - construction workers are careful to get in someone who can "talk to the elves" before blowing anything up - and officially explain them as being some of Adam and Eve's "hidden children".

Then, of course, there are the Yuletide Lads. An integral part of the country's folklore, Icelanders have had to put up with the Yuletide Lads since the 17th century. They were apparently around before then, but they hadn't yet developed into their current roles. Tradition has it that their mother, Gryla is one of the nastiest, grungiest, scariest ogres in existence. First mentioned in writing in the 13th century, one 16th- century depiction shows her with 15 tails. Each tail has 100 sacks and in each sack are 20 naughty children who she will use to make Bad Kid Stew. In fact, she makes Santa and his little list look a bit wussy.

Like their cave-dwelling mum, the Lads were a product of their environment, rural Iceland. Each Lad did something guaranteed to harass an Icelandic farming family. Apart from the Sheep-Annoyer, there is: Sausage-Snatcher, Window-Peeper, Keyhole-Sniffer, Candle-Scrounger, Door-Slammer, Leg-of- Lamb-Swiper, and half a dozen other siblings so culture-specific that understanding exactly what they do would take a degree in Icelandic socio- cultural history.

Gryla and her boys were too successful as disciplinary tools to melt under the guiding light of Christianity. So, ever practical, the Icelanders simply changed them from an all-year threat to a seasonal hazard, the Yuletide Lads. And, in spite of a 1746 decree declaring it illegal to use them to scare children, they are still the preferred way of keeping children in line during the Christmas period.

Be good and on each of the 13 days leading up to Christmas you'll get a small present. Be bad, and Gryla will make you into stew. In a particularly clever twist, Gryla has a cat whose main job is to go after children who don't get new clothes for Christmas. It makes the young ones love those itchy new socks - you have to admire that level of child psychology.

So, where does that leave Santa? Well, they haven't really figured that one out. For a while, they tried putting the Yuletide Lads in red hats and sweaters, but it didn't really work. It's hard to be threatening and jolly at the same time. So while the Yuletide Lads make appearances in parks and schools and the streets of Reykjavik, Santas are mostly consigned to malls where, as one Icelander put it, "they usually just sing and play harmonica, that sort of thing".

Icelanders have made Christmas their own by seasoning it with beliefs that grew out of their own soil. So what if it is less sanitised and more earthy. Isn't that what belief should be all about?