Like other types of blue-ringed octopus, blue-lined octopuses (Hapalochlaena fasciata) are highly venomous.
Their saliva contains a potent neurotoxin called tetrodotoxin (TTX), which they use to paralyse their prey and protect themselves from potential predators. “When it bites, the TTX-laden saliva immobilises large prey,” according to the study.
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This is the same venom that makes pufferfish so deadly – the fish accumulate TTX in their skin and some of their organs.
Now, researchers at the University of Queensland, Australia, have discovered another surprising use of the venom: during sex. Male blue-lined octopuses (Hapalochlaena fasciata) inject females with venom before mating to avoid becoming lunch, according to a new study in Current Biology.
“Female blue-lined octopuses are about twice the size of males, which bears the risk of males being cannibalised during reproduction,” says the study.
The researchers monitored blue-lined octopuses mating in the lab and found that males used a tiny amount of TTX to subdue the female before getting it on as a way of avoiding becoming lunch once the pair finished mating. The females turned pale and stopped breathing but didn’t die.
“Males use a high-precision bite that targets the female’s aorta to inject TTX at the start of copulation,” the authors say. “Envenomating the females renders them immobile, enabling the males to mate successfully.”
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Sexual cannibalism – when an animal devours its mate after sex – is common among cephalopods. As females stop eating when looking after their eggs, this last supper provides vital nutrients to help develop her young. Male octopuses have evolved ways of avoiding this untimely fate. For example, some species use a detachable modified arm to deliver their sperm to the female without having to get close to her.
Female praying mantis, green anaconda (Eunectis murinus), and redback spiders (Latrodectus hasselti) are also known to consume the male post-coitus. In the case of redback spiders, the males even catapult themselves into their beau’s mouth after they’ve done the deed – possibly to give their sperm more chance of being stored while she’s busy swallowing his corpse.
Although female blue-lined octopuses are able to resist this deadly venom, don’t be fooled into getting too close to one of these golf-ball sized invertebrates. If you’re unlucky enough to be bitten by a blue-ringed octopus, the TTX can cause nausea, paralysis and even death.
Main image: A blue-lined octopus from the study in a monitoring tank/Dr Wen-Sung Chung
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