What has 16 legs, two beaks and has been caught on camera for the first time? Two octopuses having face-to-face sex. This is just one of the unusual behaviours of the larger Pacific striped octopus that have now been documented. These creatures also have some strange hunting tactics, such as capturing shrimp by tapping them on the back, as shown in the video above.
The species was first described by biologist Arcadio Rodaniche more than 30 years ago. But its behaviour was so unlike that of any other octopus that Rodaniche鈥檚 full description was rejected for publication.
In 2012, , so at the University of California, Berkeley, and other researchers got in contact with Rodaniche to take another look at the species. Their research confirms Rodaniche鈥檚 initial observations that these octopuses are a social bunch, hanging about in groups.
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And, unusually, they mate in a beak-to-beak position, with the larger female enveloping the male in the web of her tentacles. That鈥檚 a mating pose seen in some other cephalopods such as squid and cuttlefish, but not in octopuses.
鈥淚 think many cephalopod biologists were sceptical of reports that this species lived in groups and that males and females paired for up to several days mating repeatedly beak-to-beak,鈥� says Caldwell.
This is the opposite of most octopuses 鈥� they are usually solitary creatures, only coming together to mate at arm鈥檚 length. Typically, males stretch out a specialised arm filled with sperm, which is inserted into the female. And the male doesn鈥檛 even need to stick around: during copulation the arm often breaks off and stays lodged inside his partner. The activity can also result in the female killing and eating her mate.
Fatal tap on the shoulder
So what鈥檚 the advantage of beak-to-beak copulation? The way that the octopuses align their arms and their suckers seems to help the male insert the hectocotylus 鈥� the arm that transfers sperm 鈥� says Caldwell.
But there is another reason why a mating pair might adopt the unusual pose. Females tend to deposit their eggs in a safe place, such as the inside of an empty shell, and often mate while they are still brooding a batch of them.
鈥淎t least sometimes mating occurs when the female is in a shell facing outwards while brooding,鈥� says Caldwell. 鈥淭he male approaches with his mouth facing the female. This could be the origin of the behaviour.鈥�
Larger Pacific striped octopuses also hunt with tactics that are much less aggressive than other species. Other octopuses will typically pounce on prey, ensnaring the meal in their tentacles. So Caldwell and his colleagues were surprised to see the larger Pacific striped octopus daintily extend a single arm towards a shrimp. A gentle tap allows it to successfully catch the startled shrimp, possibly by scaring it into the octopus鈥� tentacles.
Exactly why this species is social when others aren鈥檛 is still a mystery. The habitat the octopus occupies in the tropical eastern Pacific might offer some clues, says Caldwell. 鈥淭hese animals live on open muddy plains near the mouths of rivers. Suitable dens are probably in short supply, food scarce and visibility poor,鈥� he says. 鈥淭his could cause them to aggregate.鈥�
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