Where do Darwin's box jellyfish actually go from June to September?
When the question 'Where do box jellyfish actually go from June to September?' won Curious Darwin's November voting round, it posed a difficult challenge.
Box and Irukandji jellyfish are collectively responsible for upwards of 30 publicly listed deaths in the Northern Territory.
Despite this, the deadly creatures are still deeply misunderstood.
The questioner, a Darwin-based doctor who vividly recalls seeing his first body after a young boy was stung, remarked that it was odd that so little was known about strange, seasonal beasts.
Theories upheld by flimsy scientific evidence come in and out of vogue, and hearsay is common in fishing circles.
Even CSIRO's Dr Lisa-Ann Gershwin, a widely renowned jellyfish researcher, is stumped.
She's dedicated nearly 25 years of study to the creatures — which she describes as mysterious and otherworldly with an infectious joy — and the question still prompts raucous debate.
"There have been some observations here and there," she says over the phone from Hobart.
"Some of the observations have been by scientists who are paying attention, but most of the observations have been a fisherman here or a fisherman there.
"It does give us a little bit of a picture, but it doesn't answer it in the way, you know, that I as a scientist who enjoys lots of evidence would like."
Intent on broadening these disparate pieces of information into a full picture, the ABC gathers some of the most common theories and takes to the waterways of Darwin to see how they hold up.
Theory one: They die
Jim Miles can occasionally be found in a full-body stinger suit peering into the water off East Point Reserve.
Here, he dabbles in a particularly unusual sport — recreational jellyfish catching.
"In this particular spot, there is literally a plague of jellyfish behind me," he says, standing in water just a few metres out from the shore.
"I can't go more than probably four metres or five metres without seeing them or feeling them hit me on the leg."
"So yeah, plague proportions just behind me."
A group passing by shouts that there's a crocodile in the water at the other end of the beach, but Mr Miles enters the ocean unperturbed.
He wades into the knee-deep water, peers into it, and winches out a baseball-sized jellyfish as if he were retrieving a dropped hat.
On the afternoon the ABC joins Mr Miles, about half a dozen of the freshly caught creatures have got their opaque brown and lilac tentacles into a tangle in a plastic tub.
(In the course of making this story — in which no jellyfish were harmed — the ABC learned that jellyfish have well-developed eyes with lenses and retinas, much like our own.)
The larger ones will go back into the waters they were hauled from, while the smaller creatures may wind up as pets.
"When you get them in a fish tank with a nice black background and a good filtration system, they're actually really beautiful creatures," Mr Miles says.
This hobby has led him to what he believes is one reason for the vanishing population.
He has watched as the jellyfish move through their breeding cycle, getting larger and larger as the ones in wild would before reproducing.
"And then they just die," he says.
"They are basically protein-based and they basically just rot away."
"I've had one die in my fish tank, for whatever reason, and it rotted away like rotten meat."
So where are the carcasses?
While the image of dead jellyfish blooms washed ashore is a familiar one, this theory is difficult to prove with certainty.
"The evidence we have is that they don't all die — some may, but we don't know, because we've never found large numbers of carcasses year after year after year," Dr Gershwin says.
Theory two: They seek deeper water
One well-publicised incident lends credibility to the idea that the gelatinous blobs seek refuge in the deeper, calmer waters that slow their metabolisms — like hibernating deep in the sea.
In 2015, CSIRO researchers located a school of box jellyfish far off the Kimberley coastline in what is believed to be the first recording of the species in deeper water.
"This was the first true confirmation. This was incontrovertible. We had the depth, we had the … longitude and latitude," Dr Gershwin explains.
"We had all the right information that a scientist would look for to be able to confidently say 'Yep, that really happened, here's the evidence'."
The theory is appealing but there is a caveat.
There have been no official deep water observations in the Northern Territory, although Dr Gershwin says she has no reason to doubt that it occurs here.
Mr Miles, who works as a commercial diver, says he has never come across any jellyfish at depth.
But there is immense difficulty associated with tracking the population.
Sue Horner, one of the Museum and Art Gallery of the Northern Territory's natural science officers, says researching jellyfish in the Top End is deeply challenging.
Her office is stacked with jars and containers, each of them filled with preserved jellyfish, parasitic worms and other marine life, most of it pulled from the Timor Sea.
Part of the reason this vast collection has to be preserved is that jellyfish are extremely difficult to keep alive.
"They're a swift, powerful hunter in their natural environment but when you get them into an aquarium, they are quite delicate," Ms Horner said.
"It's quite tricky to get the water currents, the shape and size of the aquarium into something that will keep them alive long term."
As such, it's extremely difficult to monitor the same populations over successive dry seasons to find out what conditions they favour.
Added to this is the difficulty of monitoring water-based populations in the dangerous north.
"The territory coastline is vast, it stretches out a fair way, it can be difficult to work in, and the local wildlife doesn't help as well," Ms Horner says.
"You have to take advantage of any bits of information that come to you."
"Another theory is that [jellyfish] are only reproducing in the mangroves, which is quite possible — that is a favoured habitat for them — it just makes it a bit difficult to study up here with the crocodiles."
Theory three: They travel upstream
The final theory the ABC looked at gained traction when a north Queensland researcher stumbled upon a large number of box jellyfish polyps — the infant stage of the species — stuck to the underside of rocks in a mangrove habitat.
It gave rise to the idea that jellyfish travel upstream at the beginning of the breeding cycle to reproduce in estuaries, even though the finding was never repeated.
"Everyone you talk to says 'Oh, they breed up the rivers', but it's based on one teeny tiny piece of data that was never reproducible," Dr Gershwin says
There's also anecdotal evidence that people see baby jellyfish emerging from estuaries in spring, or in the Northern Territory, after the first big rain of the wet season.
But Ray Medlicott, who runs the kiosk at local fishing spot Buffalo Creek, which stretches into mangrove habitat, isn't convinced.
He deals with three to four stung fishermen each week, but can't say for sure if the stings are occurring upstream.
"There have been times over the years here that they've been rather late coming through the creek system, so I would say that's possible," he says.
"I did notice that during the last set of high tides we had here, I did notice a lot of jellyfish up in Buffalo Creek."
In sum, Dr Gershwin says evidence for this theory is patchy at best.
"People do say 'I caught this and it was near the river mouth'. Okay, but is that the same as coming out of the river? No, not really."
So which is it?
Bad news: there is too little concrete evidence to say for sure where the jellyfish go.
The most likely bet is some combination of all three theories.
"I actually think it's quite possible that the population does sort of divide up — some die, some go to deeper waters, some go up the waters and estuaries. That is possible," Dr Gershwin says.
Ms Horner, who leans more toward the theory that the vast majority die at the end of their breeding cycles, agrees.
"We're just really not sure where they're going and what they're doing at that time," she says.
For now, the mystery may continue to be challenged with wildcard theories and standalone anecdotes — at least until these mysterious, deadly creatures deign to reveal more of themselves to us.