The invertebrates of Prosperous Bay Plain, St Helena a survey by Philip and Myrtle Ashmole September – December 2003 Commissioned by the St Helena Government and financed by the Foreign and Commonwealth Office



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1.4. Outcomes and timetable



1.4.1. Training opportunity for Saints (September-December 2003)


Four staff from the Department of Agriculture and Natural Resources worked with the Ashmoles in the field and three of these people also gained experience in processing entomological samples in the laboratory.

1.4.2. Public relations (September-December 2003)


All opportunities were taken to demonstrate the work on Prosperous Bay Plain to other people concerned with the environment of St Helena. A talk was given to senior pupils at Prince Andrew School, two presentations relating to the background for the work were made to the St Helena National Trust, and monthly progress reports were submitted to the St Helena Government and summarised in the St Helena Herald. Discussions were also undertaken with local and visiting officials and with other stakeholders. At the end of the visit members of the Nature Conservation Group were taken to the PBP Central Basin at night to observe nocturnal spiders.

1.4.3. Production of Interim Report (December 2003)


This included background material; description of the work carried out; a preliminary habitat map of the Central Basin of Prosperous Bay Plain; outline of the results; analysis of threats to the area from airport construction; and recommendations for pre-emptive action to avoid unnecessary damage and for mitigation.

At the same time a document was submitted to the Environment Co-ordinator with suggestions for immediate action relating to the Central Basin, details of markers placed along its southern boundary by ANRD in December 2003, and calibration data for GPS instruments. A copy is attached as Appendix 2.



1.4.4. Production of early draft of Guide to Invertebrates of Prosperous Bay Plain, St Helena (December 2003)




1.4.5. Production of Final Report (target date 31 December 2004)




1.4.6. Production of final version of Guide to Invertebrates of Prosperous Bay Plain, St Helena (target date 31 December 2004)


This guide is designed for use in conjunction with the Ashmoles’ book, but with an emphasis on identification. It includes all the species found during the work on Prosperous Bay Plain and the surrounding area. It is illustrated by a large number of specially taken photographs of the species found, as well as line drawings and distribution maps for selected species.

1.4.7. Continuation of on-island and off-island publicity


In co-operation with the Environment Planning and Development team within the St Helena Government, all opportunities are taken to publicise the special nature of the invertebrate community of Prosperous Bay Plain, through contacts with taxonomic specialists, conservation NGOs (including the Overseas Territories Conservation Forum and Buglife) and relevant media.

1.4.8. Deposition of reference specimens.


Some specimens have already been deposited in museums where they have been identified (see Section 2.1.3). Others will be retained for the present, since they will be used as reference material in work on the Peaks planned for late 2005. Eventually this material will be deposited in London or Edinburgh museums, unless it is then considered appropriate for specimens to be returned to the island. Details of the whereabouts of specimens will be submitted to the St Helena Government.


    • 1.5. Constraints




1.5.1. Lack of precise data on airport footprint and routes of access roads


The response to this constraint was to try to undertake work in all of the areas likely to be affected by one or more of the proposals already floated.

1.5.2. Lack of opportunity to do seasonal work


Several species of beetles not found during the fieldwork period have previously been recorded only in the early months of the year. In some other invertebrate species where only one sex was found, it is likely that the other is adult only in certain months. The response to this constraint is outlined in Section 2.1.4.

1.5.3. Limited information on soils


The substrates on Prosperous Bay Plain show complex spatial differentiation and those in the Central Basin are evidently affected to a variable extent by leaching of mineral salts from decaying rock and from ancient bird colonies. Work by Lucy Caesar (2001) on the site of a previously proposed airport site have been utilised, as have the data on phosphates from samples obtained by the Ashmoles in 1995, but detailed work on soil chemistry would be required to gain full understanding of the situation.

1.5.4. Time required for taxonomic work


A whole year was required to organise taxonomic study of specimens obtained during the field work. Some of the species apparently represent species new to science and others require taxonomic revision, and in some of these cases full information cannot be provided even now.


2. Project execution




    • 2.1. Study area and methods




2.1.1. Study area and selection of sites for sampling


Although our terms of reference related primarily to Prosperous Bay Plain, it was always understood that we should spend some time looking at sites in the surrounding area that might constitute habitats similar to those on PBP likely to be destroyed during airport construction, and thus render loss of the latter less serious. We therefore defined an “Eastern Arid Area” of St Helena that included PBP, Horse Point Plain, Holdfast Tom and the area round Government Garage above Bradleys. Although it would be logical to include the Barn and the Turks Cap ridge in this area, neither we nor the Belgian entomologists did systematic work there and they remain largely unknown entomologically.

Within the EAA, 22 sites were selected for intensive study (see Plates 1 and 3, and Appendix 1), falling into three groups:



  • Five sites were where the Belgian entomologists had collected. It was considered useful to repeat sampling in these areas nearly 40 years later, even though the Belgians’ records were listed only as “Prosperous Bay Plain” and could not be assigned to individual sites.

  • Several sites were in the area that we assumed would be directly affected by airport construction or by the proposed access road up from Prosperous Bay beach.

  • A third group comprised sites on Horse Point Plain and on the high ground west of Fishers Valley south of Holdfast Tom, in places which had superficially similar habitats to some of those on Prosperous Bay Plain.

In addition to these 22 sites, observations and very occasional collecting were carried out throughout the area.

2.1.2. Invertebrate collecting


On St Helena there is an understandable reluctance to collect specimens, with some local people suspecting that the disappearance of the Giant Earwig and Giant Ground Beetle was caused by collection. While we are convinced that habitat loss was the primary cause of the loss of these species, collecting by the Belgian entomologists may have played a part in the final stages. It was therefore especially desirable, on St Helena, to be cautious about collecting.

However, invertebrate survey is normally based on the collection of specimens, and we remain entirely sceptical about the feasibility of carrying out worthwhile faunal surveys without the use of collecting. Furthermore, unless voucher specimens are obtained, it will be hard to convince taxonomists and the international bodies that can provide support for long-term conservation efforts, that the information is reliable.

Attempts at survey without collecting carries several dangers. First, it is strongly biased in favour of large, conspicuous and diurnal species. This bias can only be overcome by use of traps. Second, there is a real danger of making casual identifications that are actually incorrect. Without specimens, mistakes will often not be recognised and unknown species similar to known ones are likely to be overlooked.

On an island like St Helena there are special difficulties, since many of the endemic species are poorly known and available descriptions often lack illustrations. Secure identification depends on microscopic study and comparison with reference specimens from other areas, in off-island museums. Photography is sometimes a useful tool, but is often insufficient, and with small insects and spiders it is impracticable in the field.

It should also be noted that attempts at survey by observation may cause more damage than collecting by trapping. This is especially relevant to species that live under rocks, since turning over rocks causes inevitable damage to microhabitats even if the rocks are replaced. In places where refuges for animals are limited, trapping some individuals may do less long-term damage than the disturbance to the habitat when searching.

We used a combination of trapping and searching, and collected specimens except where the identity of the animals was definitely known. However, our collecting was limited to specific sites, with a set number of traps and timed searches. It was supplemented by general observations on other parts of the Plain. We are confident that our limited and localised collecting had no significant effect on the overall populations of these invertebrates.

Considerable care was taken with preparation of the traps for the fieldwork. Many of the invertebrates we were dealing with are exceedingly small, and precautions were necessary to avoid cross contamination from one site to another. The traps had to be carefully cleaned after use, and old bait destroyed. Bait was never used twice. The baits used were a beer-based attractant and preservative liquid, and strong-smelling blue cheese.

Trapping methods were those used during previous work and are fully described in Ashmole & Ashmole (2000b). At each of the sites 16 small traps (8 pitfalls and 8 small plastic bottles) were set and left for four days. This was augmented by at least 3 person-hours of visual searching and observing. By working to the same standard at each site, we are able to compare sites with reasonable confidence. GPS position, landform, substrate and vegetation information were documented and photographs were taken. Several sites were also visited at night. Additional methods of observation and collecting were used in selected areas. These comprised light trapping, hand collecting and surveys of spider eyeshine at night, shaking of branches of Samphire and rearing of larval Lepidoptera for identification of adults.

On return from the field after collecting a set of traps, the liquid bait was strained through a funnel with a very fine mesh and the traps were carefully washed out into the funnel. The collected invertebrates were then examined under the microscope, counted and recorded.

2.1.3. Sorting and identification of specimens


Identifications were made at once where possible, with the help of the reports of the Belgian entomologists (Basilewsky 1970, 1972, 1976, 1977) and entomological texts. This information was included in the Provisional Report. Subsequently we enlisted the help of a number of taxonomists, in the UK and overseas. These included staff in the entomology departments of the National Museums of Scotland and the London Natural History Museum (where many 19th century specimens from St Helena are kept), independent specialists and academics in overseas institutions. A modest budget for identification was included in the project.

Discussions during 2004 with the Environmental Co-ordinator and the St Helena invertebrate group led to the conclusion that it was impractical to store reference specimens on St Helena in the short term. It was therefore decided to deposit reference specimens of various groups with major museums and other academic institutions. In several cases such deposition was a condition of study by the museum taxonomists, and this has led to inevitable dispersal of specimens to some extent. Where possible, however, specimens are being deposited with the Natural History Museum in London, an arrangement that is especially appropriate now that there is a prospect of an entomologist from the museum working on St Helena in the future. The Royal Museum of Scotland has also received substantial numbers of specimens.




2.1.4. Sampling after December 2003


The limited length of the survey period in 2003 had the disadvantage that species which are highly seasonal in their occurrence as adults may not be found even if they have significant populations. The absence from our samples of one large and conspicuous beetle species recorded as common on PBP by the Belgian entomologists suggested that this factor was affecting our results, and several other species (some of them mentioned in Section 4.2) may be missing for the same reason.

We therefore arranged for Edward Thorpe to carry out a small amount of collecting in the early months of 2004. This led to the finding of several species not seen during the work in September to December.

We feel, however, that there is a need for additional work in the St Helena summer months, and hope to be able to carry this out during a proposed visit in the period December 2005 to February 2006.


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