Behold, the virgin birth (and yes, it's a son)

The world's largest lizard has astonished biologists by being able to produce offspring by an "immaculate" conception without the help of a male.

Two captive female Komodo dragons have had virgin births by a process called parthenogenesis, when an unfertilised egg develops into a normal embryo without being fertilised by a sperm.

The eggs of one of the lizards - a female called Flora at Chester Zoo - are due to hatch early in the new year, said Kevin Buley, one of the zoo's curators.

"Although other lizard species are known to be able to self-fertilise, this is the first time this has ever been reported in Komodo dragons," Mr Buley said.

"Essentially what we have here is an immaculate conception ... and it is a possibility that the incubating eggs could hatch around Christmas time," he said.

"We will be on the look out for shepherds, wise men and an unusually bright star over Chester Zoo."

The other female, called Sungai, lived at London Zoo until she died earlier this year of natural causes. However, DNA fingerprinting has shown that some of her offspring born in 2005 were the result of parthenogenesis.

"The fact that it has happened in two separate Komodo dragons, at two zoos and under different conditions suggests that parthenogenesis in Komodos is a lot more common than we realised," said Richard Gibson, curator of herpetology at London Zoo.

"If it can happen in captivity then the question is: can it occur in the wild?" he said.

All the offspring produced by parthenogenesis are male which, unlike mammals, are the result of two identical sex chromosomes - in reptiles it is the females that have two different sex chromosomes. The study is published in Nature magazine.

A clutch of Sungai's eggs hatched in August 2005, two years after she had been kept with a visiting male. The zoo's keepers thought that she must have stored his sperm - a common occurrence among reptiles.

However, Mr Gibson was not convinced and decided to use DNA fingerprinting to resolve the mystery. The male offspring turned out to have the same genetic profile as their mother.

"I am delighted that the mysterious parentage of our Komodo dragon babies has been solved and that we have discovered something new to science at the same time," Mr Gibson said.

"This discovery also raises important questions about the natural history of dragons in the wild and will therefore help to safeguard the future of the species," he said.

Komodo dragons can grow up to 10ft long and are the only lizards that can eat prey that are bigger than themselves. They live on several islands in Indonesia but the wild population is small, fragmented and endangered by habitat loss.

One theory is that parthenogenesis allows Komodos to establish breeding colonies from sole females that have swum to distant islands. Although the parthenogenic offspring will be all males, they would be still able to mate with their own mother to produce both males and females in subsequent generations.

"Theoretically, a female Komodo dragon in the wild could swim to a new island and then establish an entirely new population of dragons," Mr Buley said.

The saliva of a Komodo dragon contains up to 50 species of bacteria and is virulently toxic - it often kills its prey by injuring the animal first and then guarding over it until septicaemia sets in.