A colossal squid — the largest invertebrate on the planet — has been filmed alive in its wild habitat for the first time.

For decades, the Kraken-like colossal squid () was more myth than reality: scientists had only a vague sense of its appearance from fragments of its remains found in the stomachs of the whales that eat the molluscs. In fact, it was through those remains that the species was officially described by zoologists in 1925.

Finally, in 1981, fishers in Antarctica accidentally reeled up a live colossal squid in their fishing nets. Since then, the animals have sometimes been killed as fishing bycatch, or have washed ashore dead.

Last month, a vessel from the , a US-based non-profit organisation, was surveying the Southern Ocean near the South Sandwich Islands and live-streaming the footage from their remotely controlled deep-sea cameras, when an online viewer flagged that they might have just filmed a colossal squid.

Acting on the tip, the researchers sent the high-resolution footage to independent squid experts. The experts confirmed that the online viewer’s hunch was correct: the squid had distinctive hooks along the suckers on its eight arms, which are a hallmark of the colossal squid. It was roaming at 600 metres under the water’s surface.

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While colossal squids are thought to grow up to 7 metres in length and 500 kilograms in weight, the squid caught on camera was a mere 30 centimetres in length: a baby.

“It’s amazing that every time we go down into the deep sea, we find something new and exciting,” says of the Schmidt Ocean Institute.

A colossal squid in its natural habitat in 2023 by researchers from another US-based organisation, – but the sighting couldn’t be confirmed because the footage was too low in quality. The new squid recording might suggest the 2023 footage really does capture a colossal squid. “It’s the same size, same colour, similar depths, both in the Southern Ocean,” says at Kolossal, who is still awaiting further confirmation.

However, there is as yet no footage of an adult colossal squid in the wild, and the lives of these gigantic invertebrates are still mysterious, says , formerly at Auckland University of Technology, New Zealand, who coined the name “colossal squid” in the early 2000s. He once touted the animals as “seriously evil denizens of the deep” but is now convinced they are more like “giant gelatinous ticks, simply blobbing around in the water column near the seabed”.

Caribbean box jellyfish can learn from experience, even though they lack a central brain. The discovery sheds new light on the evolution and mechanisms behind learning.

“Learning is the pinnacle of nervous system performance,” says at Kiel University in Germany. Until now, researchers had generally assumed that learning from an experience and adapting a behaviour – like avoiding a hot pan after a burn – was limited to more biologically complex animals with relatively large brains, including mice, birds and primates. But some studies have hinted that simpler creatures may also have this ability, which led Bielecki and his colleagues to investigate learning in jellyfish, a group that represents a very early stage in animal evolution.

The researchers designed an experimental environment that mimicked the Caribbean box jellyfish’s (Tripedalia cystophora) native mangrove-rich habitat. They placed a fingernail-sized jellyfish in a round tank whose walls were painted with white and grey stripes to resemble the vertical mangrove roots through which the species manoeuvres in the wild.

They used grey stripes, rather than black, so that the “roots” would look further away than they were – an optical illusion that initially caused the jellyfish to bump into the tank walls. But after a seven-and-a-half-minute session in the striped tank, each of the 12 jellyfish they tested began pivoting to avoid the walls, suggesting they learned from the collisions and changed their behaviour accordingly. By the end of the experiment, the jellies had cut their crashes in half and quadrupled their successful swerves.

“After bumping into these stripes that were closer than they thought, they learned to stay further away from them,” says Bielecki. He was especially surprised that it took the jellies just a few minutes to learn to avoid the tank walls. “Previously, we thought that it took a highly developed nervous system to be able to learn anything, but now we’ve shown that this very simple, very evolutionarily-early animal is actually able to learn.”

The researchers think that, in lieu of a traditional brain, learning happens in the jellyfish’s four visual sensory organs, called rhopalium, which are embedded throughout its body. Each rhopalium has six lenses that sense light – a total of 24 eye-light lenses – which help guide the swimming jellyfish’s pulses and pivots.

The work demonstrates that “nervous systems in these animals can achieve quite striking functions”, says at the University of Fribourg in Switzerland who was not involved in the work.

We’ve finally seen how even relatively large spiders manage to take to the air. Rather than just spinning out just one or two silk fibres to catch the wind, as was thought, they make “paragliders” from dozens of thin fibres.

“The fibres are very hard to observe with our naked eyes,” says aerodynamic engineer of the Technical University of Berlin, Germany. “This is why, until now, we have not been able to explain the flight of ‘ballooning’ spiders.”

Many kinds of spiders “balloon” with the help of silk fibres that act like paragliders, travelling hundreds of kilometres with the winds. They have been found as high as 4.5 kilometres and are often among the first animals to reach new islands. Some species can also glide or windsurf.

There’s been no mystery about the ballooning of baby spiderlings, which often take to the air soon after hatching to avoid being eaten by their siblings. But it has been hard to explain how larger spiders fly.

They were thought to release only a few relatively thick, short fibres, which in theory should not provide enough lift. Instead, various exotic explanations have been proposed, such as that that exploit the ionisation of the air to provide lift.

Spiders that fly

To solve the mystery, Cho and his colleagues studied ballooning in adult ground crab spiders of the genus , which can weigh 16 to 20 milligrams. They raised some in the lab and watched them take off in a wind tunnel. They also caught some in Lilienthal Park in Berlin and filmed them taking off from a platform one metre above the ground.

They found that the arachnids are advanced aviators. Before taking off, they anchor themselves to the platform with a safety line. They then raise themselves “on tiptoe” and lift a leg to test the wind.

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If conditions are right, the spiders spin out ballooning fibres that are 2 to 4 metres long and form triangular “sheets”. Two of the fibres are made from relatively thick “dragline” silk that is 700 nanometres in diameter on average. These fibres are likely what have observed.

But the spiders also spin 50 or 60 ballooning fibres made from a much thinner silk, just 200 nanometres thick. This array of long, thin fibres should provide more than enough lift to carry heavy spiders into the air, Cho says. Other kinds of spider use these thin fibres to wrap up the prey they catch, but crab spiders appear to use it specially for flying.

If wind conditions change, the spiders sometimes cut and release the ballooning fibres, and start again.

If the take-off goes well and they climb rapidly, the spiders immediately cut the dragline anchoring them to the platform. But in slow take-offs they sometimes keep the safety line until it is 5 metres long. This means the spiders must keep spinning out the safety line as they take off, as silk cannot stretch this much.

What Cho cannot yet explain is how, with so many fibres being spun out at the same time, the spiders prevent them becoming entangled. It might be that they are electrostatically charged after all, so the fibres repel each other.