Islands - Socotra

Introduction

Located by the Gulf of Aden, midway between two war-torn states and in an area of sea plagued by piracy, the isle of Socotra is one of the most isolated places in the world. Yet should one make it there, braving the danger or in safer times to come, one would find a land, separated not merely by politics and circumstance, but by sheer geography and time: An isle of arid plains and foggy mountains, of bizarre, serpentine trees and animals found nowhere else, Socotra is a world apart.

The earliest emergence of what is now the Socotrian archipelago lies as far back as the Eocene, almost 40 million years ago (2). In the following ages, parts of the isles were submerged anew, yet not all. Come the Miocene, circa 20 mia, and the opening of the Gulf of Aden rift. The uplift following the rift pushed the isles firmly above the sea, starting the development of the Hajhir Mountains (2). Here, we might say, was the origin of Socotra as we know it: It was during this period that the last connections with the mainland were broken, that the islands were boarded, and then set adrift. From then on, the world might change, turning hither and thither, but Socotra would plot its own course.

Fig 1. Map of Socotra showing the current and potential distribution of Dracaena cinnabari. From Al-Okaishi, A. (2021).

The Fauna and Flora of Socotra

Often called the “Galapagos of the Indian Ocean”, Socotra, even in its much-degraded current state, is still a marvel of biogeography. The world’s 10th richest island for endemic plants, with 37% of its species found nowhere else, it is also home to more than 20 species of reptiles and 600 species of insects, 90% of both of which are endemic to the isle (2).

Life on Socotra is fundamentally shaped by the climate of the isle. Dry and tropical, the island is marked by strong seasonal variants, vacillating most crucially between a south-western monsoon period from summer to autumn, during which rainfall practically ceases, and north-easterly monsoon from October to April, which begins with high rainfall before gradually petering out (13). Summer rains occur as well but are lighter and almost entirely restricted to the northern parts of the isle (11) (13). This extreme cycle, between periods of intense drought and flash floods, is ameliorated only in the mountains, where the tall peaks catch the oceanic winds, creating wet refugias of fog and dew (3) (13). Here grow relict woodlands, dominated by plants such as box, Cephalocroton, and the renowned dragon blood trees (dracaena cinnabari). Though their genus is not restricted to Socotra, nowhere else in the world do dragon blood trees still form entire woods. Relics of the ancient Tethyan flora which once spanned the coasts of the erstwhile Tethys Sea, they are the last representatives of a vanished ecosystem (20) (2). Conditions are harsher in the inland hills and plains, home to arid shrubland, interspersed with scattered Socotran tree spurges (Euphorbia arbuscula) and peculiar cucumber trees (Dendrosicyos socotranus) (20). Once, the island was famous for its endemic aloe, Aloe perryi, which was grown intensively and exported in the tons (13). Today, the intense cultivation has ceased, but the plant is still found patchily across the isle. 

As with the flora, so with the fauna. As noted above, the animals of Socotra have a remarkably high endemism-rate. 180 species of birds inhabit Socotra, of which 10 are found nowhere else. Among them is the only endemic genus of birds, the Socotra warbler (Incana incana), a species with no close relatives elsewhere, possibly indigenous to the isle since its final isolation from the mainland many millions of years ago (5). Even the small, barren Abd al Kuri Island—a part of the Socotrian archipelago—is home to an endemic bird, the Abd al Kuri sparrow (Passer hemileucus), which may even be unrelated to the equally endemic Socotrian sparrow (Passer insularis) (24). Three genera of geckos are found on the islands; Pristurus, Hemidactylus and Haemodracon, of which the latter is entirely endemic to the archipelago and, like the Socotra warbler, a holdover from the original isolation of the island (23). Alongside them live a host of other reptiles, including a broad array of endemic snakes, both colubrids as well a host of burrowing blind snakes (8) (3).

Not all is well on Socotra, however, despite its uniqueness and numerous lifeforms. To understand the island’s current state, we must first put it in perspective. We cannot understand Socotra now if we do not also try to understand how it used to be. This endeavour, as we shall see, is not exactly straightforward.

Fig 2. An assortment of Socotrian vegetation. From left to right: A cucumber tree (Dendrosicyos socotranus, dragon blood trees (dracaena cinnabari) and a desert rose “bottle tree” (Adenium obesum socotranum)

Terms of use: This images are licensed under, respectively, an Attribution 2.0 Generic (attributed to Gerry & Bonni and is unedited), and an Attribution-ShareAlike 2.0 Generic (both attributed to Rod Waddington, the dracaena is cropped).

The Unnatural History of Socotra

In discussing the original fauna of a pristine Socotra, we cannot easily disentangle the story from that of human settlement. Unlike isles from Hawai’i to Madagascar, where substantial palaeontological studies have been performed, our knowledge of Socotra’s doubtless fascinating fossil history is entirely lacking (3). Even New Caledonia, understudied as it is, gives us some insight into its lost past. Nevertheless, our search is not entirely in vain. Textual sources, both from the more recent and the ancient past, grant surprisingly insightful glimpses into the island’s history, and much may be suggested by comparisons with other, more well-studied regions. 

Perhaps surprisingly, the history of hominid presence on Socotra goes back far. As early as the lower palaeolithic, 1.4-2.5 mya, there are signs of settlement by the pre-human Oldowan culture (3). The next colonisation occurred in the early Holocene, possibly upwards of 11kya, but extensive settlement did not occur until the Neolithic, perhaps closer to 3000 years ago (3). That widespread settlement across the island should be a comparatively late development is also possibly reflected in early textual records, with a source from the 1st century AD describing the population as mostly centred on the northern coast (12). The present-day language and culture of the Socotri people, which stretches back as far as written records allow, is a non-Arabic Semitic language, related to the Modern South Arabian languages of Yemen and Oman (25). In light of this long history, it has been remarked that the very survival of as many species as we have till today is somewhat surprising (5). Some species, such as desert rose “bottle tree” (Adenium obesum socotranum), have unpalatable, poisonous latex, and have escaped grazing livestock on this account. For others, such as the dragon tree and the aloes, a possible explanation is the history of cultivation, which has transported the plants around and ensured their continued survival (3). Ultimately, with no palaeontological record to study, it is impossible to estimate precisely how much has been lost. As we will soon get to, however, what little evidence we do have does not paint a pretty picture.

Oral traditions among the Socotri record several periods of demographic expansion and collapse, most often connected with droughts and food shortages. During these time, exploitation of the land became even more severe, as humans shifted to hunting land crabs, snails and land birds in large numbers (3). Indeed, much of the island once housed more people than it does today, with archaeologist D. B. Doe discovering 'many ruin sites of buildings, houses or farmsteads', and 'extensive alignments of boulder-walls... across the eastern side of the island.’ (11). Throughout Socotra, remnants of the past are readily visible. Great stretches of rocky walls span across the isle, particularly centred, as noted, on the eastern plateau. Ruined enclosures, possibly remnants of paddocks or farmsteads, dot the landscape, and the outlines of ancient field systems are still apparent (11) (13). Many of these seem the leftovers of the ancient production of frankincense, aloes, and dragon’s blood—a conclusion strengthened by the frequent overlap of the ruins with the remaining occurrences of the aforementioned plants (13).

Fig 3. Some of the innumerable ruins scattered across the Socotrian interior. From left to right: A raised grave ("mdoqo’"), the ruins of a limestone house, and the ruins of one of the many ancient walls that course the island. Images from Weeks et al. (2003).

The results of this history are still unfolding: Seven extinctions have been reported since surveys began in the late 19th century, of which four were plants and three animals. (3). Textual evidence suggests that Socotra was not always so sparse and arid as today. Once, it had flowing waterways and wider woods (5) (1).  As late as 1612 AD., the island was wet enough to support water buffalo. Today, the livestock of Socotra consists of goats, camels, and sheep. (5). Seasonal wadis still span much of the isle, but only the north-eastern Hajhir Mountains are sufficiently remote and well-watered to maintain dense stands of forest and permanent streams (11). The entire ridge of the mountains may once have been covered by thick dragon-blood forests, but today, it is not so (1): Much of Socotra’s aridity is, as prior discussed, a consequence of climatological factors beyond historical human and ecological control. Nevertheless, references to a past, more wet and fertile state of Socotra are multiple. Socotra has been no more spared from climatic vacillations than the rest of the world, and shifting climates is perhaps one factor, but there are more explanations. Tree-cover has been shown to affect local rainfall (26), catching and sequestering water in the air, as well as increasing atmospheric moisture through a process called evapotranspiration (27). It follows unsurprisingly, then, that a reduction in forest-cover, resulting from millennia of deforestation, could severely impact local humidity-levels, particularly in a region already prone to aridity.

Fig 4. The uplands of the Hajhir mountains are the only places on Socotra still moist enough to sustain running water and permanent greenery.

Terms of use: This image is licensed under a Attribution 2.0 Generic. It is attributed to Valerian Guillot, and the original can be found here. The image is unedited.

An unlikely source

Devoid of palaeontological data or useful folk memory, a tantalising glimpse into Socotra’s lost past is nonetheless provided by a most unlikely source: Roman Greece. The island is mentioned in numerous ancient sources under the name of Dioscorida, primarily on account of its exotic exports, most notably incense and aloes, as well as the valuable dragon’s blood resin, harvested from the titular trees (12) (13). Notable among these ancient sources, and for our purposes most relevant, is the Periplus of the Erythraean Sea. It is a first-century periplus—a document listing ports and coastal landmarks for use by mariners—the exact authorship of which is contested (7). Now, ancient manuscripts are of course tentative sources; a face-value acceptance of just any ancient travelogue would necessitate a belief in single-footed dwarfs, griffons, and centaurs. Nevertheless, the Periplus is, at least in its description of “Dioscorida”, entirely un-fantastical. While we cannot rely uncritically upon its claims, a cautious analysis will provide us, if not with a clear image, then at least with a tantalising suggestion of a Socotra very different from today.

Immediately striking is the Periplus’ description of the isle as “… very large but desert and marshy, having rivers in it and crocodiles and many snakes and great lizards, of which the flesh is eaten and the fat melted and used instead of olive oil” (12). This scarcely sounds like the Socotra we know yet matches well with the mentions of lost waterways and woodlands already discussed. More surprising is the reference to numerous large reptiles, all of which are absent from the isle today. A rich diversity of snakes and lizards still persists on the islands, but none of them are particularly large (8) (6). Indeed, no permanent populations of crocodiles are known from the coasts of the Arabian Sea (14) (15). On the subject of large reptiles, save for sea-turtles, testudines are unknown from Socotra (8). Interestingly, the Periplus is aware of the sea-turtles, but goes on to describe in reasonable detail what appear to be three separate species or genera of terrestrial tortoises. Here follows the text in full:

“The island produces the true sea-tortoise, and the land-tortoise, and the white tortoise which is very numerous and preferred for its large shells; and the mountain-tortoise, which is largest of all and has the thickest shell; of which the worthless' specimens cannot be cut apart on the under-side, because they are even too hard; but those of value are cut apart and the shells made whole into caskets and small plates and cake-dishes and that sort of ware.” (12)

Numerous fascinating points can be extracted from this. The clear focus in the text is the various uses of the tortoises, a fact which also lends a degree of seeming plausibility, since the animals described are not distant rumours, but instead important exports, known throughout the region. An apparent ecological distinction is drawn between the mountain-tortoise, which is also said to be the largest and most thick-shelled, and the two (presumably) lowland species. That the upland species should be the largest may seem odd, considering the typical comparative barrenness of such habitats and the general lack of mountaineering-abilities in tortoises. Nevertheless, this may in fact be a point of credibility in the text, since, as noted prior, the uplands are by far the most fertile and well-watered areas of Socotra (11). Presumably, these conditions would be more conductive to the development of larger size than the arid lowlands.

Also interesting, though much too speculative to rest upon, is the distinction between the “white tortoise” and the “land-tortoise”. Both, presumably, are terrestrial, so why list one by colour and the other merely by terrestrially? One might suggest as a possible explanation that these terms, rather than the labels of outside observers, are in fact translations of local names, which tend to be more prone to idiosyncrasies.

It seems worthwhile here to investigate the inherent plausibility of the claim that Socotra once hosted tortoises. Giant tortoises were once widespread throughout the Indian ocean (and elsewhere), having inhabited Madagascar, Mauritius, the Comoros, and numerous islands of the Seychelles (16). Of these, only the Aldabra tortoise (Aldabrachelys gigantea) remains, being one of 2 surviving genera of giant tortoises in the world. These islands are all comparatively close to each other, however, and many of the populations appear to be related (16). While the distance from the Seychelles to the Comoros is substantial, it is still much lesser than that from even the most northerly of the Seychelles to Socotra. The possibility of dispersal between the archipelagos, then, is likely very small. Nevertheless, large terrestrial tortoises have developed independently multiple times, including from the genus Geochelone on Malta, from Chelonoidis in Galapagos and the Caribbean, Hesperotestudo in North America and more (17). The genus Centrochelys in particular, of which the African spurred tortoise (Centrochelys sulcate) is the sole survivor, has produced multiple insular forms in Macaronesia (18), and has (or had until recently) a distribution stretching into Djibouti (19)—therefore reaching the Gulf of Aden, and by extension, potentially, Socotra.

All of this is to say, then, that the idea of a guild of Socotrian tortoises is in-and-of-itself entirely plausible. Indeed, from the Canaries and Cape Verde to Malta and the Seychelles (16) (17) (18), giant tortoises seem to have been almost omnipresent on the islands surrounding Africa. Socotra is an old island, with a history of isolation going back 20 million years (2)—plenty of time for it to be colonised by errant tortoises.

Fig 5. An Aldabra giant tortoise (Aldabrachelys gigantea). One of only 2 surviving genera of giant tortoises in the world, they are the last remaining in the Indian ocean.

Terms of use: This image is licensed under a Attribution 2.0 Generic. It is attributed to David Stanley, and the original can be found here. The image is unedited.

As for the report of crocodiles and “great lizards”, our considerations are similar. Crocodiles are, as noted, not known from the adjacent regions, yet the importance of this may be overstated. An old landmass with a long geological history, it is not inconceivable that Socotra could have hosted its own species of crocodile, as did Madagascar (21). Socotra is, however, a much smaller island, and one drier and less fertile even at the best of times. The most likely candidate, if the Periplus is correct, would be the Nile crocodile (Crocodylus niloticus). Much less inclined to saline habitats and open-ocean voyages than its relative, the saltwater crocodile (Crocodylus porosus), Nile crocodiles are nonetheless known to inhabit brackish deltas and saline estuary lakes (14). Indeed, the extinct Malagasy crocodile, the Voay, is relevant in this context, since its extinction circa 2000 BP led to the colonisation of Madagascar by Nile crocodiles, proving their ability to disperse across open ocean (21) (14). A final possibility, assuming the reliability of the Periplus, is that crocodiles were not in fact breeding on Socotra, but nevertheless more frequent in the seaways surrounding it at the time. The consideration of “great lizards” is much the same. There are many reptiles, including lizards, living on Socotra even to this day (8), but as observed, none seem likely candidates for the adjective “great”. Large lizards are not unknown on the isles surrounding Africa, and indeed the famous giant lizards (genus Gallotia) of the Canary Islands still preserve several extant species to this day, with extinct forms reaching nearly a meter (22). What exactly would seem an exceptionally large lizard to a Greek observer is of course debatable, but the existence of some comparatively large extinct lacertid or perhaps even a monitor lizard does not seem unreasonable.

The State of Socotra

Any survey of Socotra today is one that prompts mixed emotions. On the one hand, as recorded in the first sections of this article, Socotra remains a marvel of the natural world, home to numerous endemic animals and a flora so unique as to seem almost alien. On the other hand, as recorded in last two sections, this panoply of life we see today is but a fragment of a lost abundance, barely even remembered. The island’s long history of environmental decline is mirrored in the comparatively small role native fauna and flora plays in Socotri culture. According to one study, placenames related to animals make up only 9% of toponyms, beating only references to water, to which only 6.9% of studied names pertained - indicative of the islands desiccated state (1). Petroglyphs, found across the isle, paint a similar picture: Goats, camels and snakes alone are pictured, of which only the latter constitute likely portrayals of native fauna (4). Nor has this decline stabilised—we have noted already that seven extinctions have been counted since surveys began, less than 2 centuries ago. Long isolated, removed from the changes both of nature and of human ages, Socotra is now experiencing rapid development (20) (3). Globalisation, tourism, and illegal exportation of natural resources is swiftly taking its toll, and with little in the way of centralised governance to manage the changes, there are few signs of them slowing.

As touched upon already, much evidence indicates the Socotra of today as the end-product of centuries of habitat-degradation. An island without large native mammals, the native vegetation of Socotra was always vulnerable to introduced livestock. Though the continued persistence of the island’s rich and fantastical flora speaks to a surprising degree of hardiness, this is only to a point. With nothing in the way of palaeontological data, entire ecosystems could have vanished from the island, and we would not know. For instance, no amphibians are today known from Socotra, past or present (6), yet whether this speaks to a genuine historical absence, or a lacking awareness of extinct taxa may be questioned—the wetlands and waterways of the isle have been degraded to the point of non-existence. The situation has only worsened since the dawn of the 20th century, as traditional practices declined. Seasonal transhumance, long a way of life for most hill-herders, was increasingly replaced by permanent grazing on lowland pastures (3). This the arid soil could not bear, and vegetation-loss and soil erosion duly followed. Today, the situation is severe on the island (3) (1).

Fig 6. A forest of dragon blood trees, one of the relatively few remaining on the island.

Terms of use: This image is licensed under a Attribution 2.0 Generic. It is attributed to Valerian Guillot, and the original can be found here. The image is unedited.

What is to be done? The political situation of Socotra is not one that lends itself readily to environmental work: In 2020, the island, long insulated from the Yemeni civil war, was finally enwrapped in it when the Southern Transitional Council, backed by the United Arab Emirates, seized control of the island (28). The duration of hostilities in the region will undoubtedly decide the time until proper research can resume. We may hope, both for the people of the isle, and its natural and cultural heritage, that an end comes soon. Much work remains to be done, and there is both need and room for ample research. Ancient rock art, for instance, long understudied, has increasingly been mapped and catalogued over the last few decades, yet many sites may still be destroyed before their contents are recorded (4). Linguistic evidence and local testimony points to hitherto unrecorded sites of dragon-blood trees, still enduring in places across the island (1). Even whole populations of endemic reptiles, scattered and often fossorial as they are, could well be unrecorded. Most crucial of all, however, and most utterly lacking, is palaeontology. Here is virgin soil—an entire region of the world, unknown to the field. What such expeditions would find, one can only guess. Guess, and dream. Hidden within the caves and crannies of Socotra, forgotten for centuries, may lie waiting the bones of vanished birds and giant lizards, of broad-shelled tortoises and unknown crocodiles—gone, all gone, perhaps never even real. Yet there is only one way of knowing. ‘

Fig 7. A table of reptiles known from Socotra. Data from Sindaco et al. (2008).

Chamaeleonidae - Chameleons

Chamaeleo monachus

Gekkonidae - Geckos

Haemodracon riebeckii

Haemodracon trachyrhinus

Hemidactylus dracaenacolus

Hemidactylus flaviridis

Hemidactylus granti

Hemidactylus homeolepis

Hemidactylus pumilio

Hemidactylus robustus

Pristurus abdelkuri

Pristurus guichardi

Pristurus insignis

Pristurus isnignoides

Pristurus obsti

Pristurus sokatranus

Scincidae - Skinks

Hakaria simonyi

Mabuya socotrana

Lacertidae - “True” lizards

Mesalina balfouri

Trogonophidae - Palearctic worm lizards

Pachycalamus brevis

Leptotyphlopidae - Thread snakes

Leptotyphlops filiformis

Leptotyphlops macrurus

Leptotyphlops wilsoni

Typhlopidae - Common blind snakes

Typhlops socotranus

Colubridae - Colubrid snakes

Ditypophis vivax

Hemerophis socotrae

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