Springtail of the Month- Neelus murinus
Neelus murinus- a most unusual springtail
So, after a bit of a scramble, you’re stood outside the entrance to a cave, perhaps somewhere in Europe or North America for example, surrounded by rocks, ferns, and mosses. There’s a chill you can feel, rising out of the mysterious dark hole in front of you, as you stand in the sunshine and heat of a beautiful day. You look into the blackness and consider having a bit of an explore.
This is what a cave looks like.
Here’s what to do. Go home and don’t come back until you’ve got yourself a head torch, a spare torch and put on better footwear, warmer clothes and found a tolerant friend to bring with you for safety.
And you’ll need a loupe. You always need a loupe.
Now, as you both walk in slowly and carefully, watching your step, the outside brightness quickly dwindles into an inky blackness. Your head torches become the only light left, and there is an occasional echoing drip and plink of water falling from the cave ceiling. At this point, if you see any scatters of blackened, wet-looking bits of wood or twigs ahead of you on the cave floor, slowly and carefully pick one up. It’s more than likely that, if you can ignore the occasional boring white centipede, you will see a tiny, round, strange-looking springtail scurrying slowly and briefly into view, glowing a ghostly white in the light of the head torch. If you’re lucky, this will be Neelus murinus.
Cave animals can be split roughly into into three groups. Cavernicole or troglobite fauna can only survive in a subterranean habitat. Troglophiles can easily spend their whole life cycle in a cave system while still retaining some ability to function outside. The last group are the trogloxenes, moving between a subterranean habitat and the outside world for at least part of its life cycle but are unable to survive fully underground.
Many troglobite cave fauna show very high endemism, sometimes varying across cave to cave. Some caves can hold populations that have been cut off from the surface and other systems for many thousands of years- an entire, enclosed, temperature-regulated ecosystem, functioning in the dark and incapable of life outside, making exploring and studying caves and their inhabitants incredibly fascinating.
Springtails form a large part of any cave fauna worldwide. As with every other animal that has made a cave its home, the troglobite and troglophile Collembola have made adaptations to the dark, losing colour, sight and speed, superfluous to a life in a light-free, nutrient-poor and often inhospitable environment.
Certainly in the UK, they can be found, with some effort, in nearly every woodland, cave and dark space I’ve been in.
While very much at home in a cave, Neelus murinus isn’t just a cave dweller. As one of Europe’s most adaptable and common troglophile Collembola, it is also perfectly happy in mines, house cellars, dungeons or even in the decaying depths of woodland leaf litter.
Perhaps due to this adaptability, they have become increasingly cosmopolitan, presumably spreading across the optimum parts of the world as eggs in soil and on people’s boots and equipment. New Zealand especially has large non-native populations radiating outwards from small towns and cities, very often on disturbed ground and regenerating bush around parts of North Island, disappearing as the bush becomes more remote until only native species remain. Curiously though, in the year or so I spent on NZ, studying and photographing springtails, I never found N. murinus on South Island.
A juvenile N. murinus found in a lava tube on Rangitoto, NZ.
The largest and most distinctive concentration I ever found was on Rangitoto, a tiny, six hundred year old volcanic island situated eight kilometres off shore from Auckland on NZ’s North Island. They were everywhere. Here is my blog post about the island and its Collembola population.
For me, probably due to its unusual appearance and lifestyle, there is an undeniable, unreal magic to N. murinus. I still get a lurch of excitement every time that I find it, even after all these years.
I first found Neelus murinus by accident in the dark of a friend’s wine cellar along with a wealth of other far rarer cave species. I was aware of the species already, through photos and descriptions online but wasn’t prepared for how cool they actually were, and my heart was beating very fast when I actually got the chance to watch and photograph one for real.
Back in 2012, they hadn’t been photographed very much. I had only been taking photos of springtails for a few months at the time and the cellar was my first foray into the world of cave Collembola. I couldn’t have been luckier. Below is the first decent photo I took.
They’re the perfect springtail.
Neelus murinus in brief.
Neelus murinus is undeniably bizarre to look at, more so than its other cave dwelling springtail compatriots. Its head is angled sharply downwards, its body hunkered down as if walking with enormous effort into a cold, high wind. There are many long, straight, hair-like hollow rods protruding from its rounded back like a bristly, unshaved chin. Its body seems strange, almost off-putting, looking more like a skull than the cute, cuddly shape of a globular springtail. The lack of colour beyond a slight orange spongeing and the lack of eyes in a lozenge-shaped head also add to the strangeness, being visually so far away from its other more known and popular surface Collembola buddies.
Springtail cuticle is incredibly water repellent.
Neelus murinus was first described in 1896 by Justus Watson Folsom, who also created the family name ‘Neelidae’ to contain it. Over the intervening years, the family was slowly expanded with the addition of more genera, until eventually being elevated into the order Neelipleona, now containing six genera and around forty nine species.
Approaching N. murinus with visible head sensillar pits above antennae
Close up of sensory field on the thorax of Neelus murinus
N. murinus with visible thoracic wax tubes
It’s hard to understand what external pressures drove the Neelidae to develop such a strange look. Unlike any other springtail genera, family or order, all the Neelidae have distinctive, shortened antennae, a bulky, strongly pronounced thorax and curious sensillar pits on their heads as well as pit-like sensory fields on their ‘shoulders’ and abdomen. Their orange colour is typical of the albinism very often found in other cave animals lacking melanin.
Apart the Dicyrtominidae, the Neelidae are also the only Collembola that produce strange, waxy, hollow rods from specialised secretory crypts situated on their abdomen, as well as all sporting single rods linked to each thoracic and abdominal sensory field, possibly for chemical sensing although this is as yet unclear.
From the back, showing multiple waxy rods
Writing this blog post has meant that on my next day off, I’m paying another visit to a local Somerset cave and spending a few hours in the dark and quiet watching and photographing them. After the year that we’ve all had,, I can’t think of anything nicer.
Many thanks to Clément Schneider for allowing me to access his wonderful, definitive 2017 monograph on the Neelidae- A morphological review of the order Neelipleona….
Genetic basis of eye and pigment loss in the cave crustacean, Asellus aquaticus Meredith E. Protas, Peter Trontelj and Nipam H. Patela 2011