Saint Helena Darter—the only dragonfly of St Helena

A hotspot of insect endemism

Many people know the remote island of St Helena primarily from history: as Napoleon’s place of exile, where he was interned in 1815 and died in 1821. Beyond this prominent episode, however, the small volcanic island in the South Atlantic—around 1,800 kilometers west of the African coast—has a far less well-known but all the more remarkable significance for natural history.

With an area of only about 123 square kilometers, St Helena is one of the most isolated inhabited islands in the world. This extreme isolation, combined with its great geological age, favored the emergence over millennia of an extraordinarily species-rich endemic flora and fauna. More than 400 endemic animal and plant species are known so far, with the wealth of invertebrates such as insects and snails that evolved independently from the mainland and occurred only on this island being especially striking.

Estimates suggest that St Helena harbored around 300 endemic invertebrate species, making it a globally important hotspot of insect endemism. At the same time, this biological uniqueness proved to be an extreme vulnerability. Since the discovery of the island in the early 16th century, human intervention has profoundly altered the landscape: forests were cleared, introduced livestock destroyed vegetation, soils eroded, and invasive species spread. As a result, many highly specialized island species gradually lost their basis for survival.

The consequences are severe. Numerous endemic invertebrates are now considered extinct or probably extinct, including more than 70 insect species and 25 snail species. One of them is the Saint Helena darter—a specialized species with a small range, barely researched, long overlooked and ultimately gone without its loss being recognized immediately. Its story is therefore not only that of a single species, but also a reflection of St Helena’s ecological changes themselves.

Saint Helena darter – fact sheet

alternative names	Saint Helena dragonfly, St. Helena darter, St. Helena dragonfly
scientific names	Sympetrum dilatatum, Diplax dilatata
original range	Saint Helena (South Atlantic)
time of extinction	1963
causes of extinction	habitat loss, animals introduced to the island
IUCN status	extinct

Barely studied—and extinct

The Saint Helena darter belongs to those animal species that disappeared without ever really becoming known. Although its extinction occurred only in the 20th century, hardly anything has been handed down about its way of life. Even its scientific discovery was indirect: the entomologist Philip Powell Calvert described the species in 1892 solely on the basis of five museum specimens—four males and one female—without ever having seen living animals in their natural habitat.

The dragonfly specimens were collected during the U.S. scientific expedition to observe the total solar eclipse of December 22, 1889, which lasted from October 1889 to June 1890 and called at several island stations on its return journey—including St Helena. Calvert’s report on the eclipse expedition (1894) makes it clear that the expedition was primarily astronomical in nature. Natural history collecting took place only alongside this, as was common on many research journeys of the 19th century. St Helena was just a stopover. Without this chance find, the species would probably never have been scientifically described.

Even after its scientific first description, the Saint Helena darter remained almost invisible. There are only a few documented records, no field studies and no systematic investigations into its biology.

The only dragonfly of an entire island

In 1975, dragonfly expert Elliot Pinhey pointed out that Sympetrum dilatatum was not only endemic to St Helena, but in fact the only dragonfly species ever recorded from the entire island. This gave it an absolutely exceptional status: while even very isolated island groups usually harbor at least some immigrant dragonfly species, the disappearance of this one species practically erased the entire dragonfly fauna of St Helena.

What did the Saint Helena dragonfly look like?

The original description and museum specimens allow the external appearance of the Saint Helena darter to be reconstructed quite well. With a body length of about 4.5 to just under 5 centimeters and a hindwing length of around 3.6 centimeters (female), it was unusually large for a darter. Elliot Pinhey already pointed this out in 1975:

“It must be one of the largest species of this widespread genus.”

For comparison, most other species of the genus Sympetrum remain well under four centimeters in body length.

The Swiss odonatologist Friedrich Ris also emphasized the species’ distinctiveness in 1911. He described Sympetrum dilatatum as a very large and unusually robust member of the genus, both in body shape and overall habitus. Particularly characteristic was the strongly spindle-shaped, middle-broadened abdomen, which gave the species its scientific name dilatata (“broadened”). Several abdominal segments also bore pronounced dorsal transverse ridges, another sign of its powerful build.

The coloration was predominantly yellowish-brown to reddish; in life it was probably much more intensely red than in the preserved specimens that survive today. Males and females resembled one another closely, although the females were overall somewhat paler and showed more pronounced dark lateral markings on the abdomen.

The thoracic region was—as is typical for darters—robustly built and hairy, with several dark longitudinal lines. The wings were clear and transparent, with brownish venation and a relatively large pterostigma. Overall, the species gave an impression of compactness and resilience, more sturdy than delicate.

Despite its size, the Saint Helena darter was not a conspicuously colorful or spectacularly patterned species, but rather a comparatively inconspicuous, robust darter. In appearance, it fit well within the darter group, yet at the same time it was a distinct island species found only on Saint Helena that existed nowhere else in this form.

Traces of a barely studied species

The reason so little is known about the Saint Helena dragonfly lies not only in its rarity, but also in the special circumstances of research on St Helena. For centuries the island was difficult to reach and only sporadically investigated entomologically. Accordingly, there are hardly any systematic observations, and the few known specimens are now in museum collections—including the Natural History Museum London, the Smithsonian National Museum of Natural History and the Philadelphia Academy of Sciences.

Direct field observations have scarcely been preserved. The last secure record of the species dates from October 13, 1963, when a single specimen at Green Hill on St Helena was collected by S. D. Peters and forwarded via the zoologist Arthur Loveridge to a museum. A later date from 1977 is mentioned in the publication Freshwater Ecoregions of Africa and Madagascar (2005) as a possible last record, but the origin of this information remains unclear. Since no robust evidence exists, this later date should be considered unconfirmed.

For knowledge of St Helena’s insect fauna, however, Arthur Loveridge was of central importance. The experienced zoologist lived on the island from 1957 onward and, in retirement, devoted himself intensively to the invertebrate fauna. His assessments were based not on isolated observations, but on years of systematic engagement with the local animal world. Already at that time, he considered the Saint Helena darter to be “rare, dying out”—an assessment Pinhey quoted in 1975 from personal correspondence.

The most comprehensive scientific study of St Helena’s insect world followed in the 1960s. Two major entomological expeditions of the Musée royal de l’Afrique centrale in Tervuren (Belgium), led by Pierre Basilewsky, took place from November 1965 to January 1966 and from January to June 1967. The aim was as complete an inventory as possible of the island’s terrestrial fauna, with a particular focus on insects and other invertebrates. For numerous endemic species now regarded as missing or extinct, the results of these surveys represent the last secure records—for example for the Saint Helena giant earwig.

It is telling that the Saint Helena darter was already no longer found during these intensive and systematic investigations. Given the broad coverage of suitable habitats, much suggests that the species was already extinct at that time or was on the verge of disappearing. This assessment fits well into the overall timeline: the last secure record dates from 1963, and only a few years later the species remained unfound even during the most thorough insect inventory the island had ever seen.

From mystery to sad certainty

For decades it remained unclear whether the Saint Helena darter had truly gone extinct or had survived unnoticed. This uncertainty was reflected in changing assessments in the IUCN Red List.

After a long period without any new records, the species was first listed as Extinct. This assessment, however, was based less on targeted investigation than on the mere absence of observations. Since no systematic searches had taken place since the last secure record in 1963, the IUCN revised its assessment in 2011 to “Data Deficient”. At that time, it could not be ruled out that the dragonfly might have survived unnoticed in remote parts of the island.

Because no new records had appeared for many years, the Saint Helena darter was initially classified as Extinct. This assessment, however, rested less on targeted studies than simply on the absence of sightings. Since no targeted searches specifically for the Saint Helena dragonfly had taken place since the last secure record in 1963—despite general insect inventories in the 1960s—the IUCN revised its assessment in 2011 to Data Deficient. At that time, the possibility that the dragonfly had survived unnoticed could not be excluded.

In the years that followed, this assessment changed again. Organizations such as Buglife conducted targeted surveys on St Helena and systematically examined potentially suitable dragonfly habitats. Despite intensive searches, neither adults nor larvae of the darter family were detected. Given the size and conspicuousness of the species, it became increasingly unlikely that it had simply been overlooked. On the basis of these results, the Saint Helena darter was classified in 2018 as Critically Endangered (Possibly Extinct).

The final clarification came in 2020. Long-time island resident and conservationist David Pryce confirmed after nearly eight years of his own observations that he had never seen the species despite regular checks of suitable habitats. Together with the negative results of earlier surveys, this led to the renewed and final classification of the Saint Helena darter as Extinct.

Why did the Saint Helena darter go extinct?

The extinction of the Saint Helena dragonfly can only be understood in the context of the island’s special ecological situation. St Helena is a small, volcanic and extremely isolated island in the South Atlantic whose natural freshwater resources were limited from the outset. Permanently flowing streams and spring areas are rare—a circumstance Pinhey already emphasized in 1975 as a serious disadvantage for dragonflies, whose larvae are absolutely dependent on stable freshwater habitats. For a species living on such an island, there are hardly any ecological alternatives if these few habitats are disturbed or altered.

Before the arrival of humans, St Helena was uninhabited. Its original fauna consisted mainly of birds and invertebrates; terrestrial mammals were entirely absent. With the discovery of the island at the beginning of the 16th century, this situation changed fundamentally. Within a few centuries, the endemic bird world—apart from the Saint Helena plover (Charadrius sanctaehelenae)—was completely wiped out, including the Saint Helena rail, the Saint Helena cuckoo and the Saint Helena hoopoe. This early wave of extinction shows how sensitive the island ecosystem was to human interference—a pattern later repeated among less conspicuous animal groups such as insects.

Habitat loss as the creeping main factor

At first, St Helena served as a stopover for ships traveling between Africa, Asia and Europe. Animals were released, plants introduced, forests cleared. From 1659 onward, permanent settlement and economic use began, with profound ecological consequences.

Even the earliest interventions hit the sensitive island ecosystems hard. Introduced goats prevented the regeneration of vegetation through constant grazing, especially in the lower elevations. As a result, soil erosion increased sharply, and during rain large amounts of sediment entered the valleys and streams. At the same time, settlers’ demand for timber rose, so that extensive forest areas were cleared no later than the second half of the 17th century—including the endemic Commidendrum forests, which played a central role in stabilizing the upland ecosystems.

In the 19th and early 20th centuries, land-use pressure increasingly shifted into the island’s higher, wetter regions. Between about 1860 and 1930, tree ferns and other upland stands above 600 meters were pushed back on a large scale to make room for plantations, including New Zealand flax. In the following decades, introduced plant species additionally displaced the remaining fragments of native vegetation. Today, much of St Helena is characterized by grassland and scrub; near-natural vegetation survives only in small, fragmented upland areas that were protected only late – for example with the designation of the Diana’s Peak area as a national park in 1996.

For dragonflies, such changes have serious consequences. Their larvae live for months or years in water and require permanently flowing waters with suitable structure. Vegetation stabilizes banks, regulates the microclimate, provides shade and offers substrates for egg-laying, larval development and the maturation of newly emerged adults. If this vegetation is lost, the waters warm more strongly, dry out faster and lose quality through sediment input. On an island where freshwater is scarce anyway, every additional intervention acts not locally but system-wide.

This is an especially dangerous starting point for an endemic island species with an extremely small range. Habitat loss does not act here as a sudden event, but as a creeping process: year after year, habitats become smaller, less stable and more disturbed until the population falls below a critical size. At that point, even chance fluctuations—an especially dry year, a local intervention—can be enough to bring the system crashing down.

However, the loss of suitable habitats alone does not explain the Saint Helena darter’s complete disappearance. William Darwall and his team, who worked on the freshwater biodiversity of remote islands, point out in their 2009 analysis that, in addition to agricultural interventions, introduced species in particular are likely to have played a decisive role. This brings invasive amphibians into focus as a probable additional stress factor.

Invasive amphibians as the trigger of the final collapse

In its assessment, the IUCN highlights above all the African clawed frog (Xenopus laevis), an efficient predatory inhabitant of still freshwater that reproduces rapidly and feeds on a broad spectrum of aquatic invertebrates. On isolated islands with few water bodies, the establishment of such a species can have profound ecological consequences. Deborah A. Procter and Vin Fleming (1999) also emphasize that invasive species are among the greatest threats to biodiversity in British Overseas Territories—especially where endemic species occupy only small, fragmented habitats.

Local observations suggest that a second invasive amphibian species may have played an even more immediate role on St Helena. David Pryce reported from his own observations (roughly between 1993 and 2020):

“All one hears today in suitable habitats is the invasive, non-native frog Strongylopus grayii calling from the undergrowth; in addition, large tadpoles are often seen in still pools of streams.”

Gray’s stream frog (Strongylopus grayii) is ecologically well adapted to shallow, cooler stream systems and uses precisely those slow-flowing sections that are especially important for dragonfly larvae. Its tadpoles preferentially occupy stream pools, marginal areas and backwater zones—microhabitats that at the same time serve as development sites for dragonfly larvae.

The species originates from southern Africa and is not native to St Helena. It was probably deliberately introduced as early as the early 19th century. John Measey and colleagues (2000) suspect that the animals were originally brought to the island as food for kept ducks or other waterfowl. Concrete transport documents are lacking, but chronology and historical comments point to a deliberate introduction in the colonial context—long before the ecological consequences of such measures could be foreseen.

Tadpoles of invasive frogs are not strictly herbivorous. As omnivorous organisms, they can also ingest small invertebrates, including potentially dragonfly larvae. In addition, there are indirect effects: high tadpole densities consume space and oxygen, stir up sediments and alter water structure. In small stream systems that were already heavily stressed, such changes can considerably worsen survival conditions for dragonfly larvae—even without direct predation.

An interplay of several factors

In the end, what matters is not a single mechanism but the interaction of various factors. On St Helena, invasive aquatic predators encountered a freshwater system that had already been severely weakened. Centuries of vegetation loss had reduced the number of suitable water bodies and impaired their stability. In this context, invasive amphibians were able to exert a disproportionately large impact. For an endemic dragonfly with an extremely small range, there was hardly any room for adaptation or avoidance.

Whether the Saint Helena darter ultimately disappeared through direct predation, competition or the progressive transformation of its last refuges can no longer be reconstructed with certainty today. The interplay of severe habitat loss, natural freshwater scarcity and the establishment of invasive amphibians meant that the species did not vanish suddenly, but gradually—over decades, long before its disappearance as such was recognized.

Worldwide, only two dragonfly species are regarded as certainly extinct: the Saint Helena darter and Megalagrion jugorum from the Hawaiian islands of Maui and Lānaʻi. Both were highly endemic, both lived in isolated island ecosystems, and both vanished through a combination of habitat loss and biological invasions. Their fate stands as an example for many island endemics—species without refuges, without alternatives, and without a second chance once their sole habitat tips out of balance.

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