The fear of going into the sea after the movie Jaws has long-since ebbed away. But watch out – a very real, tiny terror is lurking in the shallows.

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Teenager Sam Kanizay’s legs and feet were left pouring with blood after he spent half an hour standing still in the sea in Melbourne, Australia. He said he felt tingling in his legs when he was in the water, but assumed it was because he was sore from playing football earlier that day.

But the bleeding wouldn’t stop and the 16-year-old spent several nights in hospital, where he was found to have hundreds of pinprick-size bites all over his ankles and feet.

His dad Jarrod returned to the beach where his son was bitten and, wearing a wetsuit and with pieces of steak as bait, he used a net to capture thousands of tiny creatures which are thought to be sea fleas or sea lice, aka amphipods.

Abundant throughout the world

But don’t think you’re safe just because you’re not going on holiday to Australia – sea fleas and their relations are found all over the world.

Aquarist Alix Harvey of the Marine Biological Association says she thinks amphipods like sea fleas probably were responsible for the Australian attack, as she has just tested their biting ability by keeping her hands very still in a tank of water containing hungry sea fleas for a few minutes.

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“I kept really really still, and they did start nibbling my skin. I did feel one take a bigger bite out of my skin, so I do think they have the capacity to bite.

“I’ve spoken to other people who’ve felt a couple of nips when they’ve been swimming late and the only things they could see were amphipods.

“The Australian boy was out at night when they come out to eat on things like seaweed and dead animals, and he kept so still for so long, so they didn’t realise he was alive and they started biting him.”

Wrong place, wrong time

She says his wounds probably wouldn’t stop bleeding as the sea fleas have an anticoagulant in their saliva.

“It probably was the amphipods, but it was a combination of factors: he was in the wrong place at the wrong time, and he stayed really still for a long period.

“It normally wouldn’t happen, and people don’t need to be scared of going in the sea on holiday. Amphipods have always been around, they’re usually very shy, and this is the only time I’ve ever heard of them actually drawing blood.”

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10 things you should know about sea fleas:

1. Sea fleas are amphipods, related to crabs and prawns.

2. They can be found “everywhere” - from the ocean to freshwater and even in back gardens.

3. There are 9,900 species of amphipods.

4, They usually measure between 1mm-20mm.

5. They’re easy prey so they like to stay hidden under rocks and seaweed.

6. They are extremely unlikely to bite, and are not normally predatory.

7. They usually feed on detritus like rotting seaweed, or sometimes scavenge on carcasses.

8. Amphipods are an important part of the ecosystem because they break down dead material which stops it piling up on beaches.

9. They are extremely abundant and usually only come out at night.

10. They are not related to dog and cat fleas.