Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world
Species: Eukoenenia spelaea
Habitat: much of southern Europe, especially the Carpathian Mountains
It's as if Godzilla had a newt for a little brother. Thanks to their vicious pinching claws and venomous stinger, scorpions are famously predatory. While the danger from the venom is exaggerated, as only a few species can actually kill a human, they're not something you want to meet on a dark desert night – unless you're the scorpion-munching southern grasshopper mouse
Their cousins, the microwhip scorpions, however, are an altogether different kettle of miscellaneous scuttling things. As their name suggests, they are tiny – just a millimetre or so long – with whip-like tails instead of stingers. But because of their size and reclusive nature, hiding from the light in soil or in the depths of caves, this was practically all we knew about them.
Cave of scorpions
Until now. An intrepid team of biologists have explored the Ardovská Cave in south-east Slovakia, where one species of microwhip, Eukoenenia spelaea, thrives.
"Most parts of the upper floor [of the cave] are covered with dark sediment rich in organic matter," says team member Ĺubomír Kováč of Pavol Jozef Šafarík University in Košice, Slovak Republic. Humans lived there during the Stone Age, he says, and they left behind a layer of ash that has enriched the soil, helping to support some animal life, including a dense population of microwhips. Their findings reveal just how wimpy these little critters are.
Rather than using their unusually large mouthparts to tear apart tiny insects or mites, the team found that the microwhips eschewed the meat of other animals, preferring a diet based on microbes.
We knew nothing about their behaviour or ecology, says Jaroslav Smrž of Charles University in Prague, Czech Republic, who led the research, but it was reasonable to expect that they were predators as almost all other arachnids are.
Cyanobacteria om nom nom
The team captured 13 specimens, dissected them and studied them under various kinds of microscope.
In the microwhip scorpions' guts, they found many single-celled organisms, which on closer examination turned out to be cyanobacteria, a type of photosynthesising bacteria that is often referred to as blue-green algae.
They also found that the microwhips' mouthparts were shaped like scissors or forceps, with edges covered with fringed teeth, like tiny hard feathers.
"These 'fringes' or 'combs' function as a toothbrush," says Smrž. The microwhip scorpion scrapes them over rocks, gathering up cyanobacteria for its food. "They also comb fungal hyphae," adds Kováč. These threads of fungi are often home to bacteria, so this may be another source of food.
It is very unusual to find an arachnid that isn't a predator, says Smrž. "Except for some mites and several species of harvestmen, most arachnids are predators." There is just one "vegetarian" spider that lives mostly on plants, and it was only discovered in 2009
Journal reference: PLoS ONE, doi.org/pgk
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