Olms – amphibious salamanders that live in the western Balkans and Italy – are extreme divers, reaching depths in excess of 100 metres in dark lakes inside limestone caves.

A team of divers and biologists has now found the curious creature 113 metres below the surface of such a lake in Croatia.

“This was the deepest finding of the olm ever recorded,” says team leader Petra Kovač-Konrad.

Proteus anguinus is commonly dubbed the “human fish” because of its pinkish pale skin, and the creatures were once believed to be baby dragons. They are noted for their slow lifestyle and long lifespan: these blind animals can live up to a century.

Little is known about olms, and it is a race against time to find out more as the salamanders’ underground habitat is being contaminated by pollution from human activities on the surface. The animals are notoriously difficult to observe in their natural habitat, except through the complex and dangerous skill of cave diving – although technology may be about to change that.

Croatian and international cave divers have found five new olm habitats in the past six years as part of the project run by . The lake where the creature was seen at record depth, Zagorska pec, is of particular interest as, unusually, several specimens have turned up there.

“We spotted specimens at many different depths in the lake, which confirms the assumption that depth of the water isn’t the stress factor for the olms,” Kovač-Konrad says. “We also noticed that olms prefer specific parts of the cave system with less stressful conditions, such as slower water flow or bigger amount of sediment.”

Recent discoveries of potential new habitats have been made using environmental DNA from cave water once it surfaces, and there are efforts to breed olms in captivity. Most observations of their behaviour involve captive animals, mainly in underground laboratories such as the ones in Postojna or Tular caves in Slovenia.

“Study of the olms in greater depths is extremely important, especially when done by divers focused on conservation,” says biologist Gregor Aljančič, head of the Tular cave laboratory. He suspects the olm will be found even deeper than the current record. “Our previous findings indicate that Proteus can withstand significant pressure.”

But it could be that the depths cave divers can reach will be the main determiner of how far down we find olms, says speleologist and biologist Gergely Balázs, of the based in Bosnia and Herzegovina.

As for conserving the animals, information about their geographical spread will be more important than knowledge of the depths they can live at, he says.

“In some caves all across the olm’s distribution range you would see only one, and in other places you would see 200 of them during a dive,” says Balázs. “And there are some places where you can’t find any, but we still don’t know why.”

Balázs’s team is now trying to install infrared cameras in the caves to film the olms going about their business.

Coral ventilation

They’ve cracked it. Small ants carry home large seeds to eat all the time, but no one knew exactly how they managed to break through the seeds’ tough exterior.

It turns out that Florida harvester ants, Pogonomyrmex badius, have developed a clever farming strategy to do so – they plant seeds, wait for them to germinate and then eat the soft spoils.

Some 18 genera of ants harvest seeds, and colonies of some species can store more than 300,000 seeds in their underground granaries.

So far, scientists thought that ants must be able to break the seeds open and just ate them as they were. “The reality is a lot more interesting,” says Walter R. Tschinkel at the Florida State University.

“There are many studies of seed choice by forager harvester ants, but none of the authors asked the question of whether the ants can open the seeds,” says Tschinkel. “This may be in part because most of these studies were done on western harvester ants whose deep nests are in hard soil, so the seed chambers are not easily excavated.”

With his team, Tschinkel excavated and studied approximately 200 P. badius nests and found that the ants mostly open and consume small seeds, which are easier to crack. Foragers collect seeds of all sizes, so this leads to the accumulation of larger seeds, which end up forming 70 per cent of stored seeds by weight.

In a series of lab and field experiments Tschinkel and colleagues showed that P. badius doesn’t seem to be able to open the large seeds unless they have germinated first. Even the caste of ants with large heads and mandibles thought to be specialised for seed opening can’t crack the big seeds.

Germination, on the other hand, splits the tough husk, making the seed contents available as food for the ants. A single large seed may have nutritional value of 15 smaller seeds, so it makes sense to collect it and wait for it to crack open. Seeds from various species germinate at different times, which may give the ants a steady supply of their “crop”.

This is the first example of ants relying on germination to consume large seeds, although some worms seem to do it, too. The only other example of ants farming plants for food is of the Fijian ant Philidris nagasau, which grows Squamellaria plants and harvests their fruit.

Read more: Crops farmed by leafcutter ants show signs of domestication; Ants use herbicide on their gardens; Worms seen farming plants to be eaten later for the first time