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Romania’s Alien Cave World of Creepy Crawlies

We like to think we have a general idea of what life is. The sun shines down, it spurs photosynthesis on this green, wet planet of ours, oxygen is created the food chain begins, and life spreads its wings. It seems as though this is common knowledge, and that it is an unchanging, immutable law of life. Yet this is not always how things are. There are places upon our planet that defy these rules, and which manage to exist and even thrive in ways that are in direct contradiction of what we think life is. These are places where life is closer to being alien than anything earthbound in nature. One such place lies within the bowels of the earth in Romania, an environment that has remained completely enclosed and cut off from the sun for millions of years, yet which has supported for countless millennia an array of bizarre life quite unlike anything else on this world. It is a dark realm of eyeless slithering, scampering creatures like something out of a science fiction movie, which have existed here in the pitch black on the fringes of our definition of life, completely independent of the sun and churning about deep beneath our feet since before humans were even a thing. It seems that one does not have to go into space to find alien worlds.

Within Constanța County, Romania, near the city of Mangalia and just a stone’s throw away from the Black Sea and the Bulgarian border, there is a desolate, barren plain bordered by the Danube River and the Casimcea Valley that seems almost as if it is the surface of another planet. Here in this geothermally active area the stark landscape is riddled with sinkholes, sulfur spewing vents, methane seeps and sulphidic mud; a perilous, harsh, forbidding place seemingly inhospitable to any life. It was here that prospecting was carried out in 1986 in order to test the area’s suitability for construction of a geothermal power plant to harness its power, and to this end a series of shafts about 30 meters deep were dug into the ground. At one point, one of these shafts broke through into a hollow area far below the ground. When workers peered down into the hole, they could see the passage leading down into the impenetrable blackness below from which belched forth large amounts of carbon dioxide and hydrogen sulphide. It seemed that the passage perhaps led down into some sort of cave far below, but there could be found no entrance to it anywhere above ground and so the prospecting expedition was cancelled and the mysterious fume spewing hole sealed up until it could be ascertained just what lay there down below in the total darkness.


The cave remained sealed off from the outside world as it had been for millions of years until after the fall of Romanian dictator Nicolae Ceausescu in 1989, when Christian Lascu, a very prominent Romanian cave scientist, dared too venture down into the murk, to a place that would prove to have been sealed off from the light of day for 5.5 million years. First he was lowered down into the shaft by rope, where he hung precariously suspended in the inky blackness, harmful gases permeating the air around him, gradually descending down into the unknown with only the bouncing meager light from his helmet fighting back the dark. After a harrowing 20 m of this drop into what could have been the mouth to Hell itself for all he knew, Lascu reached the bottom, where the sweltering temperatures reached 25 ºC and the noxious, choking gases were so thick that a breathing apparatus was required. Here a labyrinth of narrow limestone passages coated with an an ochre clay led out into the murk. Crawling through these claustrophobic passages led to a main chamber with a length of 300 metres, a total area of just 12,000 square meters, and dominated by a stagnant subterranean lake heavily laden with hydrogen sulphide which was redolent with the overpowering scent of rotting eggs or burnt rubber, and which would have choked the scientist unconscious without his breathing gear. It would later be found that underwater passages led off from the festering lake, emerging occasionally into pockets of air called air bells.

It seemed as if this toxic, inhospitable cave world of pitch black in the total absence of light would be the last place anyone would expect to find life, but it soon became apparent to Lascu that the floors and walls of the cave were literally crawling with it. Everywhere he looked or stepped things scampered, scuttled, slithered, scurried, and skittered in a nightmarish mass of pale, translucent centipedes, spiders, scorpions, insects, worms, snails, and lice never before seen by humans, as well as other less definable things that flitted through the gloom in the light of his helmet. Within the placid pool of water, thriving in its reeking hazardous fumes, were a plethora of water scorpions, shrimps, and leeches, as well as a mysterious, bizarre floating mat of frothy foam that resembled a sheet of tissue paper bobbing upon the surface. Lascu, recognizing the significance of this incredible teeming array of complex life in a cave so far below ground, in a toxic environment without any sunlight and sealed off from the outside world for millions of years, immediately left and had the cave sealed until further research expeditions could be mounted, which would go on to find that what has become known as Movile Cave was far more unique and indeed bizarre than anyone could have possibly imagined.

Within Movile Cave

Within Movile Cave

It was soon discovered that Movile Cave was completely and totally sealed off from the outside world in every way. There are no natural entrances to the cave and no passages leading to the surface. In addition, it was found that the surface of the cave is covered with a thick layer of hydrophobic clay, which prevents absolutely any water from the outside world from seeping into the cave. This is evident in the complete absence of any stalactites, stalagmites, or indeed any other evidence at all of water coming in from the surface. The water in the cave was found to be provided by a subterranean reservoir held within ancient spongy sandstones below, which gradually bubbles up into the cave. The 1986 nuclear accident at Chernobyl had also littered the area around Movile Cave with radioactive materials such as caesium and strontium, yet no traces of these substances were found in the cave, indicating that it was exceptionally well sealed and impenetrable from the outside world, with no sign of any bacteria from the surface present either. In every way, it was found that Movile Cave was completely cut off from the sunlit world above, and had been for the better part of 6 million years.

Then there was the thriving ecosystem of life down in the Stygian darkness which by all indications should not be here. The atmosphere is filled with harmful fumes and gases including hydrogen sulfide and ammonia, and has an oxygen level of only 7 to 10% compared with the usual 20%. The air here is also laden with carbon dioxide, with up to 100 times the amount typically found out in open air, and there are large amounts of methane as well. Additionally there is absolutely no sunlight down here, nor is there any organic material dripping into the cave from above or any food particles coming in with the water from below, meaning that this is an environment completely absent of any input or energy from the sun. Since there is no sunlight, there is no photosynthesis, and combined with the total lack of any organic material flowing into the cave from any source, this should mean that there is no source of food for anything to survive on here. Yet nevertheless, Movile Cave is teeming with life of all kinds, and indeed no other cave on earth is as inhospitable nor has such a diversity of interdependent species, with 48 discovered so far and 33 of those completely unique to this one cave. In fact, it seems that in Movile Cave, the worse the atmosphere gets, the more life there is. So how is this possible for such a bustling ecosystem to exist down in this harsh alien world?

Movile cave spider

Movile cave spider

The very foundation of this ecosystem is bacteria that use a process of chemosynthesis, which is using chemical reactions for energy production rather than photosynthesis. These bacteria convert substances such as ammonia and sulfides found in the cave’s geothermal waters into organic compounds. Simply put, the chemosynthetic bacteria are like the “trees” of the cave, forming the base of the ecosystem and food web. One such type of bacteria called methanotrophs oxidize the methane spewing forth here and leak nutrients that serve as food for yet other bacteria. Another is the floating film upon the water of the underground lake, which is actually a vast mat of bacteria known as autotrophs, upon which small creatures such as amphipods and nematodes graze and which are subsequently preyed on by larger and larger predators, creating and sustaining a food chain that is similar in many ways to the remote ecosystems congregating around deep sea vents, and is the only such ecosystem currently known to exist on land. These bacteria also serve to further expand the cave, as one of the byproducts of their oxidization of hydrogen sulfide is sulfuric acid, which gradually eats away at and erodes the rock over centuries to make the caves and chambers bigger. In the end, we have a totally enclosed, isolated ecosystem which creates its own space and uses energy sources completely independent of the sun to sustain large numbers of complex life down in the total blackness of the bowels of the earth.

And what unique life that is. Although there are no vertebrates to be found here, there is a multitude of species of invertebrate life of all kinds, some of which are quite large and all of which have uniquely evolved in complete isolation down in the darkness independent of the sun. All of the creatures in Movile Cave display a total absence of pigmentation, making them a pale white or even in many cases translucent, and in an environment where eyesight is pointless, none of them have eyes. Additionally, most species of insects and arachnids here have developed outsized antennae and bigger legs than their terrestrial cousins. These adaptions help the otherwise blind organisms to feel their way through the darkness, the longer limbs assist in climbing over rocky surfaces, and they are thought to also utilize chemical and electrical sensors to find their way around and to capture prey. This has resulted in an amazing array of pale slithering creepy crawlies with long legs and antennae which are horrific enough to give any arachnophobe nightmares. By 1996 alone, new species of spiders, slug, insect, centipede, isopod, a type of leech never before seen anywhere, and an utterly unique organism known as a waterscorpion, had been discovered lurking within the cave’s dark depths, and there are undoubtedly more unique organisms prowling the caves which have yet to be discovered.

Cave centipede

Cave centipede

With its forbidding environment and its walls, floor, and pools inhabited by pale slithering beasts of all manner, Movile Cave is most certainly not a place for the fainthearted. All manner of eyeless spiders, leeches, centipedes, and multi-legged things crawl through the oppressive, almost tangible darkness here and some of the slithering, scampering creatures inhabiting this alien land show some bizarre characteristics. The spiders down here still spin webs even though there are no flying insects to catch. Instead, the webs ensnare tiny insects known as springtails, which hop and bounce about into the clutches of the waiting predators. One type of spider oddly has a close terrestrial relative, which is a type of tropical spider native to the Canary Islands, lying 4000km to the west and fully exposed to the light of day. The life here is so weird, strange, and in some ways quite terrifying in appearance that it has served as inspiration for several horror movies, including Neil Marshall’s The Descent and Bruce Hunt’s The Cave, both from 2005.

All of this leaves one to wonder just how all of these creatures got down here within the depths of the earth in the first place. It is speculated that during the Miocene Epoch, about 5.5 million years ago, around when the Mediterranean Sea dried up as Africa moved north and stopped the Atlantic from flowing into it, there was a cataclysmic climactic event that forced the tropical species living above ground to find a new place to live or risk dying out. As the climate further changed, the only ones able to escape the impending doom their habitat faced were the ones that were able to adapt to living in warm subterranean caves beneath the cataclysm and ever drying environment. After that, the cave world below was sealed off from the outside world and the organisms buried in the black beneath began their evolution into what they are today. This is the prevalent theory, but it is still a mystery as to just exactly how this unique plethora of underground life took root in this perilous, isolated environment.


The unique environment of Movile Cave has much to teach us. For instance, it is thought that the conditions here are similar to what they were on primordial Earth, when sunlight was blotted out by an atmosphere thick with carbon dioxide, methane and ammonia, meaning the organisms in Movile Cave could give us clues to how life first formed on our planet. Additionally, this completely isolated, harsh ecosystem might show us how other organisms might exist in other extreme habitats on Earth, and how they can thrive while teetering on the edge of the limits of life as we know it. The ability of the cave’s bacteria to oxidize methane and carbon dioxide is also of interest, as these are the biggest causes of global warming and could give us clues on how to remove them from the atmosphere. Beyond our own planet, the lifeforms of Movile Cave can also teach us about how life might exist and evolve on other worlds across the void of space, and it has been speculated by NASA that life on Mars could have had similar ecosystems around 3.5 billions years ago when the planet was much warmer. It has even been suggested that the warm liquid water beneath the Red Planet could even now support an ecosystem perhaps similar to the one that has established itself in Movile Cave. The lifeforms here can show us what alien life on Mars and beyond might be like.

Expeditions to Movile Cave have continued to try to find answers to its mysteries, and many exciting finds are being made all of the time here. It has been ascertained that the cave may be part of an aquifer that extends over 80 square miles, and new species are being discovered here all of the time. However, exploration is carefully controlled by the Romanian Academy and the Emil Racovita Institute of Cave Sciences in Bucharest in order to preserve the fragile ecosystem and prevent it from being corrupted by the outside world. There are only certain times of year when research is allowed and a strict limit is imposed on how many people may enter and how much material can be removed for study at any given time. Only three people at a time are allowed within the cave for one hour per visit and only around 30 people have ever been inside this remote, alien realm, which is comparable to the number of people who have been to the moon. In order to lessen the chances of foreign microbes disrupting Movile Cave’s ecosystem, researchers change their clothes before entering and wear sterilized boiler suits and shoes. In the dark tunnel leading down to the cave, there is a heavy trapdoor which keeps out foreign matter.


Despite all of these precautions, the cave’s ecosystem is in danger. The very presence of humans delving into this dark domain threatens its existence, as the simple process of breathing can possibly disturb the delicate balance of oxygen and carbon dioxide in the cave, and there is no way to fully prevent small amounts of microbes from the outside world from finding their way here. The cave faces other threats as well. The steel door which is meant to keep out foreign matter is constantly being compromised by searchers scavenging for scrap metal, which authorities cannot always prevent. There is also the rapid urbanization of the nearby area of Mangalia, and this rampant development is steadily encroaching upon the area where the cave lies. The sewage systems of this burgeoning urban area, and in particular septic tanks, have the potential to leak contaminated water which could possibly somehow infiltrate Movile Cave at some point and have disastrous consequences.

The ecosystem of Movile Cave is truly alien and unique. Cut off completely from the outside world for millions of years, it has nevertheless managed to spawn a diverse array of life that has evolved independent of the sun and the realm above it. No other ecosystem on land has ever been found like this and here in its womb of darkness we could have the answers to whether alien life exists and indeed the secrets of life itself. But for how long will it remain? How long before this isolated web of life crumbles under the inexorable approach of mankind and its urbanization? How long before it is crushed by the very outside world it has managed to hide from for eons? In some ways, for all of the things it can teach us, it seems that it might have been better if the bizarre ecosystem of Movile Cave were never discovered at all. Perhaps it would have been better if it had remained sequestered and hidden away within the bowels of the earth as it always had since humans were just a glimmer in our ape ancestors’ eyes millions of years ago, and to remain a secret realm for millions more.