When the sun strikes, the worms will vanish, but if collected in time, they will be collected and treated as a delicious delicacy - the caviar of the South Pacific.

Palolo in Samoa, or balolo in Fiji, is a marine annelid worm which lives in the long barrier reefs around Pacific islands and is as mysterious for its sexual habits as it is tasty.

Once a year the worm has sex -- billions of the species all on the same day.

Before dawn on that day the rear portion of the worm, containing eggs or sperm, separates and swims to the surface, discharging its gametes in the sea.

However no-one is able to determine the exact day it will spawn.

Samoa's High Commissioner to New Zealand, Feesago Fepuleai, a keen palolo authority, recalled that as a boy there were old men who claimed to know when exactly palolo would rise.

"There were certain trees that would flower, and certain other signs and they would say when the palolo rising was happening," he said.

And up until the mid 1980s sometimes politician, police chief and fishing expert Alfonso Phillips was reckoned to know.

His record was pretty good but even he had his doubts: "It is very hard to figure out sometimes," he once said.

He has passed away and these days picking the dawn is more democratic and scientific.

It is believed to occur with the October full moon and the first high tide after that between midnight and dawn.

That is also the time of year when the sun is at its zenith, which is considered important because it provides the necessary foreplay for the worm to prepare for its big day out.

The October orgasm is for Savai'i, Samoa's biggest island, while Upolu experiences it in November.

Sometimes, such as in Fiji, the worm gets to climax twice, in October and November.

Thus using the data from Australia's National Tidal Facility the palolo rise this year will be October 20 or 21.

In Samoa the palolo rising is fast breaking news on national radio. For unknown reasons -- some suspect pollution and land use change -- palolo no longer seems to rise on Upolu's populated north-western coast and so the true aficionados take the ferry to Savai'i.

Feesago remembers his boyhood days when it rose and word quickly got around.

"Families used to give it away, but now the cash economy is in and you have to pay for it."

Sometimes the rising is heavy and prices during the morning sink rapidly; but in recent years the rising has often been light. Prices have gone through the roof and there has not been enough to go around.

Feesago, whose diplomatic postings have taken away from Samoa for decades, fondly looks forward to the little parcels that sometimes arrive; palolo in an ice cream bucket.

"I like it fried up in a little butter, and served on fresh toast. Very nice."

The butter gives it a somewhat disconcerting luminous green look to it and eating it requires a degree of faith.

SPACE.WIRE