Swaddywell Invertebrate Survey 2015
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Swaddywell Pit Invertebrate survey 2015 P. Kirby report to the Langdyke Trust March 2015 Contents Introduc9on 1 Methods 1 Sampling methods 1 Target groups 3 Nomenclature 4 Statuses 5 Recording areas 7 Survey 9metable 8 Constraints and limita9ons of survey 8 Results 9 Assessment and characterisa9on of invertebrate interest 19 Management considera9ons 21 References 23 Appendix. Complete list of recorded species 26 2 Introduc<on Swaddywell Pit has, judged on habitat character and floris9c composi9on, substan9al poten9al for invertebrates. Quarried land in general is oRen of substan9al interest for invertebrates, at least in the early to mid-stages of succession, when there is open-structured vegeta9on and bare ground in sheltered situa9ons, and varied topography. Open-structured vegeta9on and grassland on limestone is generally a rich invertebrate habitat. The site is already known to be floris9cally rich, with good popula9ons of some plants, and invertebrate diversity is, at least in some groups, correlated with floris9c diversity. The site combines quite extensive grassland on gentle topography with more varied but smaller-scale open herbaceous habitats in the quarry itself. Perhaps most interes9ngly, it has valuable wetland features, with seepages from the limestone near the base of the quarry feeding wet ground, runnels, swamp and pools. The pools, fed by direct precipita9on and run-off as well as groundwater, are seasonal or greatly fluctua9ng, leaving expanses of exposed wet silt with varying degrees of plant colonisa9on in mid- to late summer. Seepages and shallow runnels in sunny situa9ons, provided they remain wet for all or almost all of the year, are a par9cularly valuable habitat for invertebrates. Places which are permanently wet, have a constant supply of well- oxygenated water, but are never deeply flooded provide very special condi9ons for invertebrates with aqua9c or semi-aqua9c larvae living at or near the ground surface, and interes9ng specialised faunas may be associated. Good seepages are rare, because their occurrence is determined by very par9cular features of landscape and geology, and they oRen occupy a very limited area. They are easily damaged or lost - they may become shaded through neglect, they may be culverted or drained for convenience, they may be dug out to create ponds, or the land around them may be improved so that they suffer the effects of agricultural run-off. Seasonal pools, though they cannot provide habitat for some species associated with permanent water, are usually the more valuable for invertebrates, and seasonal drying, experienced also in the draw-down zone of fluctua9ng pools, prevents or slows the build-up of harmful organic material in the sediments. It is a curious feature of the Peterborough district that the invertebrates of limestone quarries are rather poorly known. Gravel pits and clay pits are rela9vely well-worked, and clay pits in par9cular figure high in the schedule of conserved sites. Limestone workings in nearby Leicestershire and Northamptonshire are rela9vely well- known. The poten9al long-term interest of limestone quarrying within the Soke is well-illustrated by Barnack Hills and Holes. But substan9al rela9vely recent workings in the area seem essen9ally unexamined. Swaddywell Pit therefore represents not only an interes9ng area of habitat at an interes9ng stage of succession, but also an insight into the wider interest of limestone extrac9on, albeit that this is one with special features that might not be widely mimicked. A survey of the invertebrates of Swaddywell Pit and the adjoining grassland, undertaken over seven visits in the spring and summer of 2015, undertook to make some es9mate of the character and value of the invertebrate fauna of the site - essen9ally, to see if the poten9al suggested by the habitats was realised. To some extent, this exercise was one of confirming and quan9fying what was already known. Limited, small-scale invertebrate sampling in previous years had demonstrated some interest in a range of groups, and in par9cular had confirmed the presence of specialist species associated with the seepages and pools. The opportunity has been taken of adding these earlier records to those of the 2015 survey, to add to the data for assessment and, in some cases, to demonstrate con9nuity of presence over at least a small number of years. Methods Sampling methods Terrestrial Invertebrates were sampled using a small range of ac9ve methods, coupled with two types of trap. Sweep-neCng 1 Samples were taken using a net supplied by Marris House Nets, with a lightweight folding circular frame 40 cen9metres in diameter and a long and rela9vely open-weave bag. The net strokes were reasonably rapid, and penetrated as far into the vegeta9on as was possible without the stroke being seriously slowed by its resistance. Sweeps were counted as single strokes of the net, either from leR to right or right to leR. A maximum of fiRy sweeps was taken before examining the catch. The contents of the net were ini9ally examined in the net, no9ng or capturing large, fast-moving or readily iden9fied species. The contents were then siRed through a 0.5 cen9metre mesh sieve onto a white tray, and the material in the tray examined for smaller and slower animals. Bea<ng Samples were taken from tree and shrub foliage by holding a sweep-net under the foliage and tapping the branch or branches above sharply several 9mes with a stout s9ck. Material was ini9ally examined in the net, then emp9ed onto a white tray for further sor9ng. Suc<on sampling Suc9on samples were taken using a petrol-driven garden leaf-blower, modified according to the method of Stewart & Wright (1998), by taping a fine-meshed net in the inlet tube. ARer three minutes of sampling, the collected material was siRed through a 0.5 cen9metre mesh sieve onto a white tray for examina9on. The coarser material was then placed on the plas9c tray and sorted for any larger invertebrates. Ac<ve search oF other key Features oF value For invertebrates Features of significance to invertebrates which were not sampled, or not necessarily adequately sampled, by sweeping, bea9ng or suc9on sampling were more closely inves9gated by close examina9on and hand searching. Aaen9on was par9cularly paid to: flowering plants providing an important nectar source; the undersides of stones, wood and other debris; liaer piles; the undersides of plant roseaes; bare wet ground. Direct observaon A small number of rela9vely large and readily iden9fied species, especially buaerflies, dragonflies, some grasshoppers and crickets, larger hoverflies, bees and wasps, were seen without the need for specific search and either iden9fied from sight or individually captured using a sweep-net. Water traps Plas9c trays, either white or painted fluorescent yellow, 40 cm by 30 across and 9cm deep, were partly filled with a non-toxic preserva9ve, composed of equal parts of glycerol and a saturated solu9on of table salt in water, with the addi9on of one drop of bio-degradable washing-up liquid per 100ml. and a small amount of Bitrex (in the form of commercial an9-dog-chew spray) to discourage consump9on by animals. The traps were placed directly on reasonably level ground. Such traps passively capture some invertebrates, but may be aarac9ve to others, especially some diptera and Hymenoptera. The traps were leR out between successive visits throughout the recording period. On servicing and retrieval, the traps were emp9ed by removing any large items of debris and filtering the contents through a fine sieve. The collected material was labelled and sealed in a polythene bag. It was preserved aRer return to the laboratory by addi9on of 70% iso-propanol. It was later cleaned by gentle agita9on in a sieve in a bowl of water to remove mud and fine debris, then emp9ed in small por9ons into a white tray and covered with a thin layer of water. The material in the tray was sorted under a bright light using a head-band magnifier of 2.5x magnifica9on. Representa9ve individuals for iden9fica9on were placed in 70% iso-propanol in Petri dishes for closer, microscopic, examina9on. In all methods of ac9ve sampling, some readily iden9fied species were noted in the field. Representa9ve examples of most species were collected for subsequent iden9fica9on or confirma9on. Most were collected using a pooter. A dry pooter made from a flexible polythene sample boale and a combina9on of rigid plas9c and flexible polythene tubing was used to capture most insects and retain them alive; for spiders, some soR- 2 bodied insects and predacious species which might do serious damage to other material if collected live into a dry pooter, a spider-pooter was used to gather up individual specimens which were then blown direct into a container of 60% propan-2-ol. dry-pooted material was kept alive un9l return to the laboratory. Here it was killed using ethyl acetate vapour, then either iden9fied immediately, or layered between sheets of 9ssue paper and placed in a labelled plas9c box for later examina9on. Aqua9c invertebrates were sampled using: • a standard pond net of side twenty-four cen9metres and mesh size one millimetre in deeper water; • a plas9c sieve of seventeen cen9metres diameter with a mesh size of approximately one millimetre in dense vegeta9on and shallow water; • a plas9c sieve ten cen9metres in diameter with a mesh size of 0.5 millimetres at water margins and to take secondary samples from areas disturbed by the larger sieve. Representa9ve bulk samples obtained by the larger pond net were examined in the net and large and obvious animals extracted immediately. Each sample was then spread on metal grids of mesh size five millimetres suspended over plas9c trays, and ac9ve animals were allowed to make their own way through the grid for a minimum of ten minutes while the sieves were employed in the capture of addi9onal material from shallower areas and the pond net in a search for addi9onal large and ac9ve species.