Survey of the shrill carder bee Bombus sylvarum, at the proposed solar farm at Llanwern, Gwent Levels - 2017

D. C. Boyce & A. P. Fowles

DC Boyce Ecologist August 2017

1. INTRODUCTION AND METHODS

1.1. The author was commissioned to carry out a survey of the shrill carder bee Bombus sylvarum on land that will be affected by the proposed Llanwern solar farm on the Gwent Levels. The location of the survey site is shown on Figure 1. The land included within the proposed development lies within the Nash & Goldcliff Site of Special Scientific Interest (SSSI) and Whitson SSSI. The shrill carder bee is a strongly declining species, for which the Gwent Levels constitute one of its last British strongholds. The area also supports a strong population of a second declining , the brown-banded carder bee Bombus humilis.

1.2. The Gwent Levels are an area of coastal grazing marsh that are known to be of high ecological interest. This interest is primarily associated with the aquatic flora and fauna found in the extensive network of drainage ditches (known locally as reens). However, the shrill carder bee is also a qualifying feature for these two SSSIs. The shrill carder bee is a Nationally Scarce species, which is listed in Section 7 of the Environment (Wales) Act, 2016 as a species of principal importance for conservation of biological diversity in Wales. The brown-banded carder bee is also included in the latter list.

1.3. The survey was carried out over a two-day period, on the 1st and 6th of August 2017, with these dates being dictated by weather conditions in early August (very unsettled, with generally cool, wet, windy conditions). The timing of the survey coincided with that when peak numbers of shrill carder bee workers and males are found (August). The site was divided into 55 survey units, corresponding to the individual fields into which the study site is divided. These are also shown on Figure 1. Survey was carried out in every one of these survey units within the application site. It focused on recording foraging workers at favoured nectar and sources, such as red Trifolium pratense and common knapweed nigra. A ‘W-walk’ was carried out across each field that aimed to come within 10 metres of all stands of flower-rich grassland and hedge and ditch margin where there were stands of potential nectar/pollen sources. This means that survey time was considerably greater in those fields where there was still unimproved/semi-improved grassland. In fields that were cut, heavily grazed or where there was flower-poor improved grassland, survey was restricted to a boundary walk looking at ditch and hedge margins, where there was sometimes still a strip of flower-rich habitat.

1.4. In each survey unit, all bumblebee species were noted, with the number of shrill and brown-banded carder bees being counted, along with the flower species at which they were seen foraging. Where possible, were identified in the field to species level, with any specimens of ‘difficult’ species netted for examination in a tube with a hand lens. Fortunately, the shrill carder bee is easily distinguished in the field. Workers of the white- tailed and buff-tailed bumblebees (Bombus lucorum and B. terrestris respectively) are indistinguishable without microscopic examination. As these are both very common and widely distributed species, they were recorded as B. lucorum/terrestris. Males and queens of these two were recorded to species level. Note also that B. lucorum is a complex of three very similar sibling species, which are only reliably distinguished by DNA analysis. For the purposes of this study, all records of ‘B. lucorum’ refer to the B. lucorum aggregate.

1.5. Section 2 of the report sets out the results of this survey and following this in section 3, there is a discussion of the results that includes thoughts on the importance of the site for the shrill and brown-banded carder bees and on management and mitigation measures that might protect and/or enhance the populations of these species in the context of the proposed development. Figure 1. Location of Llanwern study site and survey units, shrill carder bee survey, 2017.

2. RESULTS

2.1. Table 2.1 shows the nine species of bumblebee (including the Bombus lucorum/ terrestris aggregate) that were recorded in the 55 units surveyed in August 2017. Figure 2.1 maps the distribution of these records across the study site, along with thenumbers of individuals noted at each of these. 91 individuals of B.sylvarum were recorded from 17 of the survey units. The most important concentration of records was in the most westerly block, which is part of the Nash and Goldcliff SSSI. Of the 91 adults recorded across the site, 74 were found in this block, with numbers of up to 19 recorded here (in survey unit 29).

Table 2.1. Bumblebee species recorded at the Llanwern study site, 2017. Species Status No. adults Survey units Bombus sylvarum S7, Nb. 91 1,5,8,27,28,29,30,31,32,33,34,35,36,37,40,41,44 S7 168 1,2,3,4,5,6,7,8,19,26,27,28,29,30,31,32,33,34,35,36,37,40, Bombus humilis 41,44,46 Bombus hortorum - - 1,6,8,27,28,29,30,31,33 - - 1,2,5,6,8,10,19,20,22,23,27,28,29,30,31,32,33,34,35,37,40, Bombus lapidarius 44,45,46,49 Bombus lucorum - - 27,37 Bombus - - 1,2,3,5,6,7,8,11,19,20,21,23,24,25,26,27,28,29,30,31,32,33, lucorum/terrestris 34,35,37,38,39,40,41,44,45 - - 1,2,5,6,7,8,9,19,20,23,27,28,29,30,31,32,33,34,35,37,42,43 Bombus pascuorum 45,46,49 Bombus pratorum - - 1,2,8,29,30,33 Bombus terrestris - - 2,5,8,30,32

Table 2.2. Flowers visited by scarce bumblebees at the Llanwern study site, 2017. Species No. B. sylvarum No. B. humilis Centaurea nigra 5 39 Cirsium arvense 1 Cirsium palustre 7 5 Cirsium vulgare 61 67 Dipsacus fullonum 3 3 Lathyrus pratensis 1 7 Lathyrus sylvestris 1 Lotus glaber 5 Lotus pedunculatus 2 1 4 Rubus fruticosus 1 Trifolium pratense 3 Trifolium repens 1 14 cracca 11

2.2. As can be seen in Table 2.2, the, the vast majority of shrill carder bees were found nectaring on spear thistle Cirsium vulgare. Marsh thistle Cirsium palustre and common knapweed Centaurea nigra were the only other flowers visited in significant numbers.

2.3. Table 2.1 shows that B. humilis was more widespread and abundant than B. sylvarum, with 168 individuals recorded across 25 of the survey units. As with B. sylvarum, most observations came from stands of spear thistle in the westernmost block, but significant numbers were also recorded elsewhere on common knapweed, white clover Trifolium repens and tufted vetch . The greatest number of individuals was in the unimproved survey unit 8, which was very flower-rich, with large stands of common knapweed, upon which the majority of B. humilis were found.

Figure 2.1. Numbers of shrill carder bee Bombus sylvarum by survey unit.

Notes on Tables 2.1 and 2.2: The number in front of the dash is the survey unit and that after refers to the number of B. sylvarum (Table 2.1) or B. humilis (Figure 2.2) recorded there. Figure 2.2. Numbers of brown-banded carder bee Bombus humilis by survey unit. 3. DISCUSSION

3.1. The study site supports a significant population of the shrill carder bee. The largest concentration of records is in the western block of fields, lying immediately to the east of Chapel Road and the Chapel Reen (survey units 27 to 36). These group of fields have a rather species-poor, semi-improved sward characterised by an abundance of rushes Juncus spp. and thistles. There are large stands of creeping thistle Cirsium arvense and spear thistle, as well as scattered plants of marsh thistle. Spear thistle was much the most significant source of records for both shrill and brown-banded carder bees during the current study, though a few individuals were also seen visiting marsh thistle.

3.2. The choice of flowering plants visited by the shrill carder bee has varied considerably between the various bumblebee surveys; Smith (2010) recorded the flowers visited by 1018 B.sylvarum workers, 62% of which were visiting plants in the family Fabaceae such as narrow-leaved everlasting-pea Lathyrus sylvestris, tufted vetch and common bird’s-foot-trefoil Lotus corniculatus, with a further 17% noted on common knapweed. Other studies on the Gwent Levels have shown creeping thistle to be an important nectar/pollen source for the shrill carder bee (Pavett, 2004). In this context, it was interesting to note that during the current study, much of the creeping thistle was beginning to set seed, but even where there were flowering stands, it was striking how both scarce bumblebees ignored the flowers of this plant and sought out patches of spear thistle growing amongst them.

3.3. There is still a large population of the brown-banded carder bee within the study site. Again, stands of spear thistle in the western block had the largest numbers, with 67 adults recorded. However, common knapweed was also a very important nectar and pollen source, especially in survey unit 8. This latter field had the most unimproved grassland anywhere across the study site and was very flower-rich, with large stands of knapweed, and bird’s-foot trefoils. 21 brown-banded carder bees (and 1 shrill carder bee) were recorded here.

3. DISCUSSION

PAVETT, P.M. 2004. The status of the shrill carder bee Bombus sylvarum on the Gwent Levels. Countryside Council for Wales Contract Science No. 623. CCW & National Museum of Wales, Cardiff.

SMITH, M. 2010. The status and distribution of the shrill carder bee Bombus sylvarum on Magor & Undy SSSI and Whitson SSSI on the Gwent Levels and on Newport Wetlands National Nature Reserve in 2009. Countryside Council for Wales Contract Science No. 919.. CCW, Bangor.