Lifesavers in Far North Queensland have shared a video showing just how surprisingly tiny the highly-venomous Irukandji jellyfish are.

It shows the potentially deadly jellyfish swimming over a $2 coin to put its size in perspective. 

“This is what we mean when we say Irukandji really are THAT small!” the post on the Australian Lifeguard Service in North Queensland’s Instagram page reads.  

Cairns senior lifeguard Jon Murray told 9news.com.au that it was almost impossible to spot the Irukandji jellyfish in the water, a fact that surprised many people.

“In some of our huts we have specimens in formaldehyde jars, and a lot of the feedback we get is, I knew they were small, but I just didn’t know how small,” Murray said.

Murray said that, contrary to public perception, the stinger nets set up in some Far North Queensland beaches did not protect swimmers from Irukandji jellyfish.

“The stinger nets themselves are made to stop the box jellyfish, a much bigger, much more lethal type of jellyfish,” he said.

“It cannot, and does not claim to stop the Irukandji.

“That’s why we advise people, especially anyone with any sort of cardiovascular history, to wear a microsuit when swimming inside the net.” 

Researchers had predicted this singer season, which runs from November to May, would be much quieter than recent years because of ecosystem damage from floods from Cyclone Jasper. 

However, this had so far proven not to be the case, Murray said.

“The researchers weren’t expecting much, but we have started catching some stuff that has caught them off guard a bit.” 

“We just want to get the message out that the stingers are actually there, so please swim between the flags, and the stinger net for safety.”

Murray said it was not always easy to tell straight away if a swimmer had been stung by an Irukandji jellyfish, as there was often a delay of about 20 to 40 minutes before the symptoms appeared.

“The sting is not always that giveaway, by any means, with Irukandji,” he said. 

“But as soon as the symptoms kick in, it’s very telling and very obvious.” 

The first true sign of an Irukandji sting was usually a patient reporting they had a sore lower back, Murray said.

“The way that the patients have described it to us. It’s like having a cricket bat slam in your back over and over and over that just starts to spread throughout the body as the poisons hit the lymph nodes,” he said. 

“So as soon as the patient says, I’ve got a sore lower back, that’s when we escalate and close the beach.”