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

2.1.2. Invertebrate 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

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.