Invertebrate survey for UKBAP and Red Data Book species

Posted by Michael Williams - AIEEM BSc (Hons) on 1/12/2010

Ecosulis was commissioned to undertake an invertebrate survey on a small brownfield site in Newport, Wales, following on from a Phase 1 habitat survey, data search and correspondence with the council ecologist. From these, the site was considered to have suitable habitat for the UK Biodiversity Action Plan (BAP) shrill carder bee, the UK BAP small ranunculus moth and the Red Data Book ground beetle Amara fusca. Ecosulis has previously undertaken surveys for the shrill carder bee in Wales and have a good knowledge of ground beetle identification, amongst other invertebrate groups.

Arriving on the site, a quick site walkover was undertaken to assess the key habitats for the target species and areas where other species of note may be found. While undertaking the walkover I also searched for prickly lettuce, the foodplant of the small ranunculus moth, which was recorded during the Phase 1 habitat survey. The survey was timed to coincide with the appearance of the larvae on the foodplant. The absence of prickly lettuce recorded on site made it unlikely that the small ranunculus was using the site for breeding. The habitats on site were then divided into sections:

  • First was the areas of sparsely vegetated waste ground, consisting of concrete, bare earth and sand. These areas contained mugwort, the foodplant of Amara fusca
  • Second was the grassland, which contained a variety of flowers. Although no typical foodplants of the shrill carder bee were present, this habitat was considered worthy of search for bees and other grassland and nectar-feeding invertebrates
  • Third was the scrub and trees adjacent to a small stream at the bottom of the site, which could harbor a variety of invertebrate species

Next, Ecosulis set about installing pitfall traps across the site. These were mostly concentrated around the areas with suitable habitat for Amara fusca, but also placed amongst scrub, trees and grassland. Consisting of a plastic cup with a small amount of preservative, these are designed to catch ground-dwelling invertebrates. Several water traps were also laid throughout the site, consisting of various-coloured dishes filled with water and a dash of washing-up liquid, to collect flying invertebrates. Once these were in place, searches began within the target habitats.

As it was still relatively early in the day and most of the site was still shaded, there was little invertebrate activity. Ecosulis staff therefore began by looking for signs of invertebrates. Firstly the dead branches and trunks of the hawthorn trees by the stream were searched, looking for the exit holes of the nationally scarce hawthorn jewel beetle. Many wood-boring beetles are difficult to detect from the exit holes, but the hawthorn jewel beetle makes obvious D-shaped holes in hawthorn. The search yielded no exit holes. I then searched the trees and shrubs for galls and leaf-mines. Galls are swellings in plants caused by a reaction to the presence of an invertebrate, often a larvae of a fly, sawfly or a wasp (but also adult mites and several other invertebrates). Many species can be detected by the types of galls present and the species they are present on. Even closely related species of gall-causers on the same plant can produce very different galls. Leaf mines are caused by the larvae of various invertebrates, usually moths or flies, eating their way through the inside of a leaf. Many species can be identified to species level by the shape of the mines. Several of the galls and leaf mines Ecosulis staff were familiar with and able to note down without removing, however a small collection of some of the more difficult ones was taken for later identification. Ecosulis also did some beating of the branches, by holding a tray underneath them and hitting the branches with a stick to see what fell off. Several spiders, weevils, an earwig and an orange ladybird landed in the tray and those that couldn’t be identify in the field were collected in a pooter and small tubes of alcohol for the spiders (which tend to eat other specimens, including other spiders, if left in with them) for later identification.

Attention was then turned to the stones and other debris across the site, particularly in the waste ground area. Ecosulis soon found an uncommon species of pill woodlouse (the ones that roll up into balls), Armadillidium nasatum, which was present in high numbers, along with Britain’s largest harvestman Odiellus spinosus, an uncommon introduced species that is infrequent in Wales.  A specimen of each was taken for comparison with Ecosulis's surveyors collection of reference specimens, in order to confirm their identity later. Several small spiders and beetles were found, which were collected for later identification. The infrequent ruderals on site, particularly those with flowers, turned up several interesting and unusual species.

By now it was starting to warm up and bees, flies and butterflies were beginning to fly around the site. With nectar feeders, we find it easiest to wait for a few minutes by different species of flowers. Different types of flowers attract different species of invertebrates, for example clovers are often frequented by bumblebees, but not so much hoverflies, for which hogweed and ragwort often support a wider range of species. Many of the nectar feeders encountered (usually the large or the obviously-marked species) are species readily identified in the field, such as honey bees and the hoverfly Episyrphus balteatus, but of those that are not, or could be confused with other species, voucher specimens to check later. Surveyors also used their ears to listen for grasshoppers and crickets, and heard the calls of meadow grasshopper, field grasshopper and long-winged conehead, the latter of which was considered a rarity, confined to southern England until recently. Surveyors later saw specimens of these three species and was able to confirm their identity. Butterflies were also frequent around the grassland, but all species were common, such as common blue, large white, painted lady and speckled wood.

Having spent a good hour or so on each of the key habitats, Ecosulis proceeded to revisit them, collecting further specimens and making notes of species that were not present the first time around, and looking at the wider environment and the potential for rare species to colonise the site in the future. The surveyor also left the apple core from their lunch in a sunny spot and was able to catch several wasps and flies feeding on it in the afternoon. Just before leaving the water traps were collected, which did not contain much except for a few flies. Specimens of these were pit in alcohol.

Following the survey, Ecosulis proceeded to identify the voucher specimens in the laboratory, working through identification keys and using a microscope where necessary, particularly for the smaller specimens such as the majority of spiders and some of the smaller beetles. A further terrestrial invertebrate survey and moth survey were also undertaken on the site, as well as several collections of the pitfall traps, which yielded an almost completely different set of species to those collected on the walkover surveys. Amara fusca was not among them, but a specimen of the Nationally Scarce dung beetle Onthophagus vacca was found.

Collecting voucher specimens, while not desirable from a conservation perspective, is a necessity for a large proportion of invertebrate species, as many of them require careful examination under a microscope, sometimes involving dissection, and comparison with reference specimens in order to reliably identify them. Responsible collecting, where only sufficient numbers of specimens are taken in order to identify them is not considered to be detrimental to populations, in fact in many cases it benefits them. Good mitigation and conservation schemes depend on the reliable identification of invertebrate species.

Once the identifications were completed, Ecosulis was then able to put together site-specific recommendations for the site, tailored to the species that I found there and species that may eventually colonise the site. This included the provision of food plants for species present on site and recorded in the data search, a mosaic of brownfield, grassland and tree planting in the undeveloped areas of the site, the retention of dead wood and a general planting list for urban invertebrates.