Unexpected Inhabitants of the Namib Desert
Written and photographed by Oliver Halsey
When exploring the vast Namib Sand Sea one may come across the occasional small rock, as seemingly lifeless as the surrounding area. Upon lifting the rock, a pseudoscorpion or two may be found - kilometres away from other visible life forms, let alone civilization. Pseudoscorpions are tiny creatures, several millimetres long, resembling scorpions yet lacking the tail or stinger. Occasionally found perching on flowers, they can wait for flies, bees, or butterflies in order to catch a ride by clinging to a leg and then detaching themselves whenever it is deemed suitable, hence these tiny terrestrial arthropods showing up in distant and remote places. In 1969, biologist Peter Weygoldt wrote in his aptly named academic book The Biology of Pseudoscorpions, “Sometimes I am asked why I study animals so unimportant to human life and economy as pseudoscorpions. There is one simple answer: every aspect of nature that interests the human mind is worthy of study whether or not it is of direct importance to man” (Weygoldt, 1969).
Why are small forms of life important or worthy of study? A perpetual question that often troubles biologists and taxonomists. World over we are losing species by the day, more often than not due to anthropogenic causes; yet life persists regardless of diversity loss, filling gaps in any available niches. The problems however, are we simply do not know of all species that are vital to the sustained functioning of an ecosystem, or the long-term implications of such rapid species loss.
To serve as an example there is a small, green species of fly known as the !nara fly, of which science knows very little. (The ! and ≠ symbols are used to denote click sounds in the Nama language). The fly is thought to be found only on the !nara plant in the Namib Desert. !Nara is of fundamental anthropological, biological, commercial, and historical importance. !Nara has provided a valuable source of food for indigenous peoples for thousands of years (Sandelowsky 1974). The ≠Aonin Topnaar, current indigenous inhabitants of the Namib-Naukluft and Dorob National Parks, still harvest !nara, crucial to their cultural identity and lifestyle. !Nara demonstrates its growing commercial success with products such as !nara soap, oils, lotions, and seeds (Henschel, et al. 2004). !Nara also serves as a critical fortress and source of food for many organisms; its thorny stems protecting small animals from predation and providing stability in sandy soil, enabling many creatures to create burrows. In 2013 scientists produced evidence showing that, among other tiny insects, the !nara fly is a pollinator of the plant (Beitler, et al. 2013). We do not know the full impact the fly has upon the plant, but its potential significance as a pollinator is huge, regardless of its physical size. If the fly were to suddenly disappear, the decrease in !nara pollination would result in a drastic reduction of fruit. Modern biodiversity loss has resulted in a global concern for pollinator conservation since food supplies worldwide are reliant on tiny insects such as the !nara fly.
Traversing the desiccated terrain of the Namib Desert, one could be forgiven for believing that they had been transported to another planet. The Namib Sand Sea, a majestic yet inhospitable body of dunes, flowing over some three million hectares, engulfs the land with its parched grasp. What decades of research, documentation and observation on the Namib has told us, however, is that it is anything but inhospitable - at least for the countless desert-adapted organisms that grace its scenic grandeur.
The diverse array of specially adapted organisms found within the Namib never fails to impress. Countless creatures have evolved to contently inhabit this otherworldly environment, such as burrow-digging geckos, scorpions and spiders, or the beetles, which conjure up inventive ways to exploit the regular fog to obtain necessary moisture. These organisms and many others have captivated generations of curious minds. Often one can physically see and therefore logically understand the extraordinary evolutionary adaptations bestowed upon these creatures, which enable them to survive in hyper-arid conditions. Whilst one may be able to deduce that many of these desert-dwelling inhabitants belong to this environment, merely by observing physical traits, beneath the surface lie some rather unexpected, logic-defying residents - snails.
Terrestrial snails are present in many of the world’s deserts, and the Namib is of no exception (McMichael, 1966; Schmidt-Nielsen, et al. 1972; Hodgson, et al. 1994). Snails are often associated with wet areas; so learning that they exist here may come as a surprise. Parts of the Namib seldom see rainfall and some years may go by without any at all (Lancaster & Seely, 1984). Incredibly some snails have evolved to exploit infrequent rainfall, lying dormant for months or even years at a time and then surfacing shortly after heavy rainfall or on damp, foggy nights and mornings at certain times of the year (Curtis, 1991a; Dallas & Curtis, 1991).
Certain snails have been observed to bury themselves several metres below ground surface (Sirgel, W. pers. comm.), entering a state of dormancy. When the snails are dormant, water loss is dramatically reduced to the point where some species can survive for several years without moisture (Mendelssohn, 1963; Yom-Tov, 1971). Upon rare desert rainfall seeping into the sandy soil, snails can emerge for a limited time to feed and reproduce before cosily burying themselves beneath the surface once again.
There have been reports of snails emerging from their subterranean dwellings in droves, making walking across the surface without crushing their shells impossible, only for them all to completely disappear ten minutes later at sunrise, with even digging not revealing the slightest evidence of the prior mass-congregation (Sirgel, W. pers. comm.). A snail from an arid region of northern Africa, originally thought dead, was once glued to a plaque in the British Natural History Museum, only for it to emerge from it’s shell four years later after water had been applied to the plaque (Allen, 1889). For creatures that are often overlooked or disregarded, they are certainly capable of some truly incredible feats.
At Gobabeb, a scientific research station in the central Namib Desert, several snail shells have been lying in and around a small fenced-off enclosure on a remote interdune area for many years. The shells have baffled many-a-scientist, their origin a mystery. Several of these shells were recently sent to an expert in South Africa, Dr Willem Sirgel, who identified them as Trigonephrus haughtoni, a relatively large terrestrial species of snail, which has been previously found and studied in the southern Namib (Curtis, 1991a) but never in the Gobabeb area. “The fact that no living snails have been seen [at Gobabeb] is not so strange”, explains Dr Sirgel. “Trigonephrus spends most of its life underground [and] I can only come to the conclusion that if there are shells, there must be some snails at least nearby” (Sirgel, W. pers. comm.). Dr Sirgel proposes that the snail shells in and around the enclosure plot may be a result of birds preying on them and then carrying them there, perching on the fence, the only high perch point on the otherwise barren interdune, and then discarding the shells after having consumed the contents. Has the mysterious origin of snail shells around Gobabeb’s enclosure plot finally been solved?
Throughout history the Namib has cycled through wetter and drier climatic periods (Stone & Thomas, 2012), which leads to another theory - that the snail shells are thousands of years old and Trigonephrus species do not occur in the Gobabeb area anymore. Present-day rainfall patterns across the Namib might lead to Trigonephrus preferentially occurring in the southern but not the central Namib. Deep in to the Namib Sand Sea there are areas known as paeleo-lakes, which once held significant volumes of water (Teller & Lancaster, 1986; Teller, et al. 1990.). Stone Age tools have been found at these ancient lake beds (Shackley, 1985), now completely dry and inhospitable to man, as well as calcified stem casts of Phragmites (Teller et al. 1988) - common reeds that occur in areas where freshwater is present. Stones show the unmistakable signs of being carried and shaped by water (Teller, J.T. pers. comm.). Ancient animal tracks also exist in a remote area of the Sand Sea. The animals wandered across the mud, which then hardened, preserving their spoor for thousands of years (Sandelowsky, 1976). Shells of freshwater snails dating back to around 13,000 years (Vogel & Visser, 1981) have also been found at these sites. It is possible that the shells found at Gobabeb are just as old, if not older. An archaeological excavation of a cave in the southern Namib revealed charred Trigonephrus haughtoni shell remains - the snails had been collected, cooked, and presumably eaten by hunter-gathers in the last two millennia A.D. (Kinahan & Kinahan 2003). The archaeologists state that the palatability of the snails is, however, unfortunately unknown.
Temporary desert pools
Although fog is fairly frequent in parts of the Namib Desert, unpredictable and occasional heavy rain can fall, which presents remarkable opportunities for the formation of desert-adapted life. The sudden surge of water can form temporary pools that may last for days or several weeks at a time (Seely, 1987: 49). Usually the gravel plains of the central Namib appear barren, dry, and devoid of life - reminiscent of a Martian landscape. Heavy rainfall can quickly transform the land; lush grass sprouts, covering the desolate expanse with a carpet of green. Insects abound; dragonflies dart, and numerous other creatures with aquatic larval development can be found fluttering along or swimming around (Day, 1990). Dragonflies are normally associated with wetter areas, requiring water for their larvae to develop. This immediately seems problematic for dragonflies found in the Namib. The species Sympetrum fonscolombii can be found in the Namib Desert but is not a desert endemic. S. fonscolombii can migrate to arid areas during the rainy season and is opportunistic in its water body selection. (Suhling et al. 2003; Suhling & Martens, 2007: 227). S. fonscolombii larvae have been observed to hatch from eggs on the second day after having been lain (Suhling & Martens, 2007: 14) - not just a useful adaptation to areas containing only short-lived temporary pools, but also believed to be a world record for dragonfly egg development.
In early 2017, some 50mm of rainfall was measured near an inselberg (an isolated mountain rising from a plain) located on the central Namib gravel plains. Angela Curtis and Dr Gillian Maggs-Kölling of Gobabeb, examined a temporary pool that had formed and observed small creatures swimming around in the shallow and murky water. Those creatures were tadpole shrimps, or Triops - primeval shrimp-like crustaceans that have endured on Earth for some 250 million years (Longhurst, 1955). The temporary pool was in an area of the Namib Desert that has unpredictable rainfall patterns; the eggs of these Triops had been lying dormant for months, even years, in soil temperatures that have been known to reach above 60 degrees Celsius (Lancaster & Seely, 1984).
Constrained to their small and temporary world, the life of a Triops is undoubtedly intriguing, yet seemingly inconsequential to our own. However Triops have been anything but irrelevant to humanity. Found throughout the world, certain Triops species have been used by scientists for an impressive host of practical applications. Triops are used to control weeds in Japanese rice paddy fields (Takahashi, 1977) and have also been found to deter mosquitos from laying their larvae, as well as consuming the larvae (Tietze & Mulla, 1991), thus reducing mosquito populations and their attributed diseases. Most impressively, Triops have been launched into space to board the International Space Station (ISS) to study as a potential high-protein astronaut food for future long-term missions (NASA, 2014). Dormant Triops eggs have even survived the outer space conditions outside of the ISS for a continuous period of 13 months (Novikova, et al. 2011). In addition to an already impressive résumé, some Triops eggs can survive water temperatures up to the boiling point (Carlisle, 1968). The point of listing these studies is not to justify scientific experimentation, but to illustrate that there is more beyond the first impression of a small, cannibalistic living fossil, confined to a fleeting ephemeral world.
The desert’s secrets are far from being entirely revealed, and an appreciation for its ever-enchanting forms of life can be enriching to observe. To paint a picture of the Namib, many have emphasised the unrelenting heat and aridity, unceasing winds, and with them, the bombardment of miniscule sand grains. The presence of aquatic animals, so unorthodox to the predictable stereotype of the sterile waste known as the desert, instils a sense of childlike wonderment. It is common knowledge that the adaptations of certain desert organisms are disparately alien to our own physical bodies, yet an appreciation of the overlooked or unknown can illuminate an unexpected novel world of awe and admiration.
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All images are copyright © Oliver Halsey.