Notorious sex pest of the animal world has the perfect excuse for serial groping

Pity the poor male greater blue-ringed octopus. And pity his girlfriends as well.

The native of Australia is notorious as the king groper of the animal world, famous for fondling its partners with a specially modified arm before mating. But researchers from California have discovered that far from being a sex pest, poor old Hapalochlaena lunulata has a perfectly reasonably excuse for his behaviour.

Scientists from the University of California discovered that the octopus, who is common to the Pacific and Indian oceans, does not initially know if he is dealing with a male or a female and is as likely to grope one as the other. Finding a partner is a shot in the dark.

The researchers, Mary Cheng and Roy Caldwell, writing in Nature Australia magazine, studied 15 encounters between male octopuses and nine between a male and a female.

In each, the aroused octopus reached out its modified arm, or hectocotylus, and caressed the other octopus.

If the octopus realised he was touching another male, the sexual encounter was quickly, but amicably, halted. But if he discovered he had found a female, the male would insert his arm under her mantle and release his spermatophores in a two-hour copulative effort.

Previous research shows that the female octupus's troubles do not end with this indignity. Soon after mating, the female begins to lay 60 to 100 eggs, which she then guards closely for the next 50 days.

But because she stops eating while protecting the eggs, the mother dies almost as soon as they hatch.

The researchers were taking a chance going so near. The octopus does not produce ink but makes a poison similar to the tetrodotoxin found in deadly puffer fishes. The venom in its saliva will subdue or kill its prey and is lethal to humans.