Captain Cook's bean snail

Partula faba

Partula faba was the first Partula to be recorded, based on shells collected on Captain Cook's first expedition in 1769. Thomas Martyn named it 'Limax faba' without explanation; it has little, if any, resemblance to a bean.

Unusually for a Partula, and unique amongst French Polynesian species, it was found on two islands: Raiatea and Tahaa. Its extinction on Tahaa probably occurred in the mid 1990s and the last survivors were collected on Raiatea in 1992. Since then it survived only in captivity but never prospered. This is strange for, as a relatively large snail, it might be expected to be quite robust. It was found from sea level to the top of Raiatea so should be tolerant of a wide variety of conditions, and as one of the most widespread of the Partula it should have been adaptable, but it wasn't.

Over the past 20 years the captive population has declined slowly. They bred, but always at slightly less than the replacement rate. By 2015 just one snail survived.

Urgent research tried to identify the vital factor needed to save them. Could it be a special feature of the diet? With no wild populations to study and so few survivors it is a difficult question to answer. Old specimens preserved in museums were studied in the hope of finding the key. Surprisingly the first ones to be dissected were found to contain ants. It seems unlikely that this snail was a specialist ant-eater, and it is more likely that the snails were feeding on fruit, and consumed the ants accidentally (although they did contain a very large number of ants). Other specimens contain a wide range of plant fragments, suggesting that this is naturally a generalist. A greater range of food items was offered to the captive snails in the hope that this would stop their decline. Unfortunately the snails showed no interest in the unfamiliar food. On 21st February 2016 the very last Partula faba died. Heads of ants found within Partula faba

On 21st February 2016 the last surviving Partula faba died in Edinburgh Zoo. This was a significant event in Partula history: the 34th partulid extinction and the loss of the first species to be described, 232 years ago.

Partula faba was the first live partulid that I encountered, in Vaiapu valley on Raiatea in September 1992. Euglandina had passed through that valley just days before, leaving a carpet of empty shells of P. faba and P. garrettii. Just a single live P. faba remained. Over the next week I did find more in valleys that had not been devastated by Euglandian at that time, but those I collected on the Temehani plateau on 8th September 992 were the last sighting of the species in the wild.

The single Vaiapu snail lived on in London Zoo for six months, during which time it produced several offspring. Initially it seemed as though P. faba had been saved, as the 65 that I had collected and the 89 brought back by the Operation Partula Expedition the year before survived and bred. However, although the wild collected snails did well, subsequent generations never prospered and gradually the population dwindled. As different zoo populations declined the colonies were brought together at London Zoo, but the declines continued. They were then moved to Bristol Zoo which had fewer Partula and was better able to concentrate on this critical species. This also did nothing to slow the decline and in 2015 the last two were moved to Edinburgh Zoo which had experience of pulling Partula back from the brink, having rescued P. tohiveana from a bottleneck of four. By the end of the year just one remained. Self-fertilisation had occurred once when the species was more abundant, so even then there remained a faint hope of recovery. Sadly the last one died before that could occur.

The loss of P. faba epitomises the problems facing partulids: their vulnerability to extinction in the wild and the difficulty of maintaining them in captivity. They coexisted with humans for about 1,000 years, and most have been capable of withstanding habitat changes and intensive collection, but have been unable to survive Euglandina introduction. Being small and comparatively simple to keep, it is relatively easy to keep large populations in captivity. However, identifying exactly what they need for sustained breeding, or the causes of decline, have proved extremely difficult. For P. faba my research into the diet of the specimens that Crampton preserved failed to identify any key component that could have saved them. Similarly, pathological studied have failed to identify any specific cause of death.

For P. faba the story is probably over. As a large and highly conspicuous tree-snail there is no realistic possibility of its continued, undetected survival in the wild. In recent years there has been much talk of resurrecting species through techniques such as cloning. This is well advanced for mammals, but we are a long way from developing the necessary techniques for an ovoviviparous snail. However, P. faba has been included in the ‘Frozen Ark’, the repository of material that may one day allow this to move beyond science-fiction. It is not a coincidence that Partula are well represented in the Frozen Ark, set up by Bryan and Ann Clarke, and Ann McLaren. Initially based on preservation of the DNA of the Moorean Partula species, the Frozen Ark is yet another example of how Partula have inspired developments in science and conservation.

Other research on Partula