A South Beach resident finds a deadly blue-ringed octopus lurking in her swim trunks

A beachgoer has survived a fatal encounter with a deadly blue-ringed octopus after finding one in her swim trunks after a swim.

Lisa Bryant was swimming at South Beach in South Fremantle, southwest Perth, when she made the shocking discovery on Thursday.

A 7cm blue-ringed octopus emerged from a shell she had just placed under her swim trunks for safekeeping.

The quick-thinking local caught the creature in a coffee cup and removed it from other swimmers, but not before snapping a picture of it.

A blue-ringed octopus bite has venom powerful enough to kill over 20 people, although the sea creature is small, typically around 8cm long.

Luckily, Lisa Bryant was not bitten by a blue-ringed octopus (pictured) who was found in her floats crawling out of a shell she found in South Beach, southwest Perth

Ms Bryant frequently collects seashells and puts them under her floats, claiming she always shakes them to make sure there’s nothing in them.

She didn’t see the squid until about 20 minutes later, when she started to feel the shell irritating her.

“When you swim in South Beach, don’t be tempted to pick up shells from the seabed,” Ms Bryant wrote in a Facebook post.

‘[I] pulled out said shell and flopped out a blue ringed octopus – my lucky day.’

According to the Department of Biodiversity, Conservation and Attractions, a bite does not cause pain and tracks are often difficult to find.

“I quickly checked to see if there were any marks and I had a small scratch,” Ms Bryant told Perth Now.

“I started freaking out and everyone on the beach freaked out and told me to go to the hospital.”

The blue ringed octopus contains venom powerful enough to kill over 20 people in minutes despite the creatures only being 8cm long (blue ringed octopus pictured).

The venom, called tetrodotoxin, causes paralysis and slows the body to the point where it can’t breathe and doesn’t get enough oxygen.

There is no antidote for tetrodotoxin, and victims of a bite can only outlast the toxin on a ventilator until its effects wear off.

Although the danger is serious, there have only been a handful of confirmed casualties from a blue-ringed bite, as the creatures tend to hide in small crevices rather than attack.