80
Suffolk Natural History, Vol. 34
WASPS AND BEES (HYMENOPTERA) IN THE SUFFOLK SANDLINGS AND MANAGEMENT FOR THE CONSERVATION OF THESE INSECTS. M. EDWARDS The Suffolk Sandlings form a distinctive coastal strip of heathland, lying roughly between Lowestoft to the north and Felixstowe to the south. These heathlands have developed on tracts of light, sandy soils, underlain by clays which occasionally reach the surface or which may be brought to the surface by agricultura! or forestry Operations together with calcareous ragstone outcrops. They have climatic, physical, florisitic and faunal features in common with the extensive Brecks to the north-west, but also, perhaps surprisingly, with the band of heaths developed over light sands at the western edge of the Weald. In particular there are several species of bees and wasps which are found on both the Wealden Edge heaths and the Sandlings, but not on the Brecks. The Sandlings also share their relative lack of entomological recording with the Wealden Edge heaths, both areas being overshadowed by larger, more accessible, areas of heathland fairly nearby. However, in both the Sandlings and the Wealden Edge heaths, the small scale patchwork of light sandy heath, clay and calcareous outcrops present provides a great diversity of potential niches in a small space, leading to a high local faunistic diversity which has only recently begun to be appreciated. DĂźring 1996 and 1997 I was commissioned jointly by English Nature, the Royal Society for the Protection of Birds and the Suffolk Wildlife Trust to carry out a survey of the aculeate Hymenoptera of the Sandlings in order to provide a modern assessment of the importance of the Sandlings for this group of insects and to provide management advice for their conservation. This latter aim was particularly relevant in the context of the opportunities for heathland conservation and restoration within the Sandlings Project. The surveys were made at selected target sites within the Sandlings with visits made during April, May, June and August. Although this was the most systematic and far-ranging survey known to us it still falls far short of what is needed to provide a thorough coverage of the aculeate Hymenoptera of the area. Hence, it is expected than many more species will eventually be found in the Sandlings. The main areas surveyed were Walberswick, Minsmere/ Dunwich and Blaxhall/Tunstall, with occasional visits made to Westleton, Leiston and Sutton. Survey was by direct Observation and hand-netting, as many aculeates need to be examined under the microscope for accurate identification. Prior to this survey, information on the aculeate fauna of the Sandlings was available by sifting the information given in Claude Morley's 1935 paper on the Hymenoptera of Suffolk; a short report on a number of Sandlings heaths by Michael Archer in 1987 and the species list compiled by Lee Chadwick for her book 'In Search of Heathland'. Of these sources, Morley's paper needs to be used with great caution, being a compilation of earlier published records; several times he lists the same species under different names, giving different comments each time! Archer's survey was, like the 1996/7 one, targeted on a
Trans. Suffolk Nat. Soc. 34 (1998)
WASPS & BEES IN THE SUFFOLK SANDLINGS
81
selected sample of sites; however, these were only visited during July (one site had been visited ten years earlier during August). Mrs Chadwick's data was compiled through observations at one site (the now sadly degraded Leiston Common) over a number of years; however, Mrs Chadwick was not an specialist entomologist and many species will have escaped her notice. She did, wisely, take the precaution of sending specimens of the species she noticed for expert identification and her records are therefore well validated. The total number of species recorded throughout the 1996/7 survey stands at 176 out of a total of about 600 UK species. Of these, 3 have a conservation rating of RDB3, 10 have a conservation rating of Nationally Scarce a and 11 have a conservation rating of Nationally Scarce b. Many of the species recorded are new for the Sandlings and some are new for the Watsonian vice-county of East Suffolk. A large number of the species found during the survey are typical of light sandy heaths and acidic grasslands, including a number of species with close association with Erica and Calluna heaths. Several species stand out for particular mention: Sphecidae (solitary Digger Wasps) Crabro scutellatus (Nationally Scarce a). Only previously recorded (post 1970) from one location in the Sandlings. This species is typical of damp areas bordering dry sands on the heaths of the western rim of the Wealden Basin and the Hampshire Basin and is on the northern edge of its ränge in the Sandlings. Oxybelus mandibularis (Nationally Scarce a). One male found in a spider's web on Tunstall Common. It is previously recorded as present in East Suffolk on the basis of one pre-1970 record from near Lowestoft. Diodontus insidiosus (RDB3). One male was found on Westleton Heath NNR. This species has not previously been found further north than the River Thames. Ammophila pubescens (Nationally Scarce b). Several heaths had good populations of this heather heathland associated wasp, which has its main distribution on the heaths of the western rim of the Wealden Basin and the Hampshire Basin. It does not, apparently, occur on the Brecks, despite several intensive surveys carried out in suitable locations. This species is the probable host of the RD3 Bombylid fly, Thyridanthrax fenestratus. Although the fly was not seen during the present survey, it should be looked for on the Sandlings. Podalonia affinis (Nationally Scarce a). This large digger wasp is largely restricted in distribution to the East Anglian Brecks and Suffolk Sandlings. It is typical of the grass-heath areas where it extracts its prey, large noctuid caterpillars, from inside grass clumps. Cerceris ruficornis (Nationally Scarce b). One female at Westleton Heath NNR. This site is towards the northern edge of its ränge in the UK and represents its only known location in Suffolk. The wasp is associated with heather heathland, preying on weevils.
Trans. Suffolk Nat. Soc. 34
(1998)
82
Suffolk Natural History, Vol. 34
Apidae (Bees, mostly solitary) Hylaeus pectoralis. This bee utilises the interface between reed-bed and dry grassland, nesting in the vacated cigar galls of the fly Lipara lucens on common reed and foraging on the flowers of the grassland. It was considered a specialist of the fens but has been shown to be more widespread in south-eastern England. It is very vulnerable to over-enthusiastic management of reed beds, which may destroy its nesting site. There are several other specialist aculeates of this habitat. Of these, the RDB3 wasp Passaloecus clypealis has been recorded from Walberswick in the past and is probably to be found elsewhere in the area. Andrena argentata (Nationally Scarce a). This small bee is closely associated with heather flowers and nests in loose bare sand on heathland. It was not known from Suffolk before Lee Chadwick's specimens were taken. The males taken at Minsmere were foraging at a Mayweed (Matricaria sp.) by the visitor centre. In this location it is likely that the female foraging site (heathers) and the nesting site (loose bare sand) were separated by some distance. Andrena labiata (Nationally Scarce a): this species is particularly associated with Germander Speedwell, Veronica chamaedrys. Its decline since the early years of this Century is thought to be attributable to the loss of permanent pasture in the modern agricultural landscape. The group of bees Andrena bimaculata (Nationally Scarce a), Andrena tibialis (Nationally Scarce a) and Nomada fulvicornis (RDB3) where the Nomada is the cleptoparasite of the two Andrena species. All three species seem to be largely restricted to light sandy heathlands and associated open woodlands. Lasioglossum brevicorne (RDB3). Another bee with a strong affinity with sandy acidic grasslands. It is associated with yellow 'dandelion-type' composite flowers, where it collects the pollen and nectar which it uses to provision its nest. Sphecodes reticulatus (Nationally Scarce a). This cleptoparasitic bee was not recorded from Suffolk before Lee Chadwick's specimens. It occurs here in similar habitats to those in West Sussex: heather and heathy grasslands on light sands and where its supposed host, Lasioglossum prasinum, is, at the least, scarce. It is possible that it is associated with two closely related Andrena bees, A. barbilabris and A. argentata, as has been suggested by Continental workers. A further two species of particular interest were recorded by Lee Chadwick but were not found during this survey: Anthophora bimaculata (Only known from Suffolk on the basis of a 1799 specimen from Woodbridge before Lee Chadwick's specimens were taken.) and Lasioglossum prasinum. The first species may be more typical of the cliffs than the open heath and the recent extensive erosion of the sandy cliffs may have affected the species badly. The second species is associated with heather heathland and may be expected on the dry sandy heathland of Dunwich and Westleton Heaths. Before considering specific aspects of management for the conservation of the aculeate Hymenoptera of the Sandlings some general points about insect life-styles need to be made. Many of the larger, more strongly flying insects have many parallels with birds in the way in which they utilise partial habitats within the overall habitat. These partial habitats may not exist in close
Trans. Suffolk Nat. Soc. 34 (1998)
WASPS & BEES IN THE SUFFOLK SANDUNGS
83
proximity, but each provides some resource, e.g. juvenile food (prey, pollen or other plant resource), adult food, mating area, nesting site or nesting materials, which is needed during the insect's life history. This utilisation of partial habitats is particularly well developed in those species which provide food for their young in nests, the bees and wasps and ants. The loss of just one of these partial habitats is crucial to the survival of the insect species. In addition to this, most insect life-cycles are just one year long, with no stage regularly able to survive for several years. Hence even a temporary removal of one partial habitat can spell disaster for the population. However, due to the mobility allowed by having wings, populations show an amazing ability to exploit new resources, if all other conditions are correct. In this context, the recent population explosion of the bee-wolf wasp Philanthus triangulum (see plate 7) is instructive. For over a Century this wasp was known to have only one stable population, on the coast of the Isle of Wight. In addition to this, occasional records from East Anglia hinted at another population based in the Brecks or Sandlings. Over the past five years the species has spread to many parts of southern and mid-England. This increase is thought to relate, at least in part, to a slight increase in late summer temperatures. It follows from the above considerations that habitat management for insect populations needs to consider the fine-scale habitat mosaic within an overall habitat type. The assessment of such a mosaic needs to recognise both the species compositions (animal and plant) present and the physical structure, including the presence or absence of bare ground, flowers and nesting resources. Many insect populations are associated with dynamic, but small-scale systems, and management needs to provide small, but frequent, change in the overall habitat. One of the most neglected aspects of this small-scale change is the need for a constant supply of bare ground and the Vegetation communities which follow disturbance. Such Vegetation communities often provide a local, but highly concentrated, source of flowers, an essential partial habitat for many insect populations. Most Calluna heath systems in the UK are excessively even-aged and often over-mature, with a preponderance of aged Calluna and a lack of earlier successional plants, including Erica cinerea, an important early flowering heather. I suspect that the Silver-studded Blue, Plebejus argus, has a streng association with Erica cinerea, both flowers and leaves. Certainly there are plenty of colonies of suitable Lasius ants in localities, both in the Sandlings and elsewhere, where there are no Silver-studded Blues; suggesting a more complex interaction than just the presence or absence of suitable ants. Elderly heathers also produce relatively less leaf and flower than younger plants, thus providing fewer resources for the insects associated with them. Some species are associated with old heathers and areas of such aged plants should be left. The aim should be to maintain a variety of age and physical structures, including strips of bare ground, within the heath. The presence of areas of scrub, including bramble, within heathland is a positive benefit. Such scrub provides shelter, a variety of food resources and mating points. Small oaks are very valuable in this respect. A balance must be Struck between the need to
Trans. Suffolk Nat. Soc. 34
(1998)
84
Suffolk Natural History, Vol. 34
reduce nutrient aggregation and the Provision of larger scale structure. This may require coppicing of scrub on a relatively short cycle. Regeneration of heathers by mowing goes some way towards creating structural variety, but tends to leave the peaty humus layer beneath the plants intact and often does not create the bare ground needed by many insects. Past uses of heathland by man include the removal of this peaty layer for use as a fuel. Small-scale burning and scraping on Calluna-dominated heaths are dynamic management techniques which need further research and development. Both produce excellent insect habitat. It is noticeable that two wasps (Diodontus insidiosus and Cerceris ruficornis), which are normally found much further south, were found at the experimental heather management plots on Westleton Heath NNR. These plots should be maintained and the scope of the experiment expanded to include investigation of the effects of ground disturbance within Calluna-dominated heath. It is also not clear what the route of ecological succession on old Calluna-dominated heath is and some plots should be left undisturbed to investigate this. Whilst there is a guild of insect species specifically associated with open Calluna heath, many insects associated with heathlands in their wider sense are there because of the physical conditions present, rather than the presence of heathers. Heathlands develop over nutrient poor soils, which are frequently of a sandy nature. It is the physical characteristics of the sand which are important. Such soils are easily dug, making the digging of burrows relatively easy. They also warm up readily in the spring and cool down quickly in the autumn, making the micro-climate more suitable for insects requiring a continental-type regime than would otherwise be the case in the UK. Acidic grasslands are a much neglected aspect of the heathland ecosystem. They have developed, perhaps on slightly more fertile areas, as a response to grazing pressure. The species-poor grassland left after removal of bracken may not bear much resemblance to the original grassland, although renewed grazing may prove these areas to be readily improved as habitats for insects. Small areas of what may have been more typical grasslands were present during the survey on the northern edges of Dunwich Heath and the southern side of Westleton Heath. A good (for insects), flower-rich, grassland was often present in the rides and cleared areas of the forestry areas. Such areas need not hold great plant rarities, as some very 'common' plants, such as Ragwort, Senecio jacobaea, and the various dandelion-like yellow composites, are excellent forage plans for insects. Limited disturbance of the soil is likely to bring buried seeds to the surface as well as provide a slight local increase in nutrient levels, and investigation of the effects of disturbance management should be included in any research program linked to grazing management on the Sandlings heaths. Grazing management (and its artificial counterpart, cutting) may not be an unqualified benefit for insect populations. The intensity and frequency of grazing are important considerations. Herded animals did not graze the same area day in day out. The result of the movement of grazing stock over the, then extensive, Walks would have been the development of a matrix of Vegetation structures, with some areas near villages being fairly heavily grazed all the
Trans. Suffolk Nat. Soc. 34 (1998)
WASPS & BEES IN THE SUFFOLK SANDLINGS
85
time, but others, further away, only intermittently grazed. Under these conditions a proportion of plants would have always been in flower within flight ränge (up to 3km. for the larger bees) during the relevant season. Many plant foliage-feeding insects need a particular vegetative structure to thrive. Under a modern, fenced-grazing system in a restricted area it is all too easy for the plants to be maintained, as non-flowering rosettes, whilst the insects dependent upon them starve. It should be noted that there is a guild of insects, not assessed under th current survey, which are dependent upon the seed-heads as well as those dependent on the flowers and other vegetative parts. In several places within the Sandlings, most noticeably at Minsmere (Visitor Centre) and the south-western end of Sutton Common, very large populations of rabbits were resulting in extensive over-grazing and a consequent loss in resources for insect populations. Whilst it may not be possible to revert to a herded grazmg system, it is important to plan grazing regimes to allow some areas within a habitat to remain ungrazed for considerable periods. These areas should also be rotated to allow them the benefits of being exposed to a grazing regime. A guide is that grazed areas are frequently at their most productive for grassland associated insects in the first three years after grazing has stopped. Similar rotational grazing should be applied to grazed Calluna-dominated heath, where continually present grazing animals suppress the flowering of plants growing in the small 'lawns' between the heathers. Bare ground has been mentioned as a desirable part of a successional mosaic within the Sandlings system. Permanent, or near-permanent, areas of bare ground, often on a steep slope where soil instability or extreme drought contributes to the maintenance of the bare areas, are also important, particularly as nesting areas for bees and wasps. The creation and maintenance of small cliffs and banks is a very valuable small-scale habitat management technique. Vertical root plates from wind-blown trees can also provide small dry soil areas suitable for nesting by aculeates. Some aculeate species utilise horizontal bare ground areas, some utilise vertical areas, hence both situations should be provided. , . Good (fortuitous) examples of this management exist at the car-park in Tunstall Forest, where banks created to delineate parking areas are readily used by the local insects. Other examples are at Minsmere (where a small quarry has been created to encourage nesting by Sand Martins), and Dunwich Heath. Here a small exposure of clay has been created to supply material for use elsewhere on t h e Site. A n extension of this quarry area would create m o r e habitat and
carry out »uiiic some valuable , . nuiyJ uui vaiuauis. scrub jviuu control. vu..uv.. . . . . . to i - forestry . i resulted in in aomajor momr reduction r^nurtion in in The conversion of„ heathland has extent of the Sandlinas heaths. However, such change of use may not result in
when the heathers are out ot tlower; 11 is nie n c a u . - v ^ , — diversity of flowering plants, which supports the largest number ot species.
Trans. Suffolk Nat. Soc. 34 (1998)
86
Suffolk Natural History, Vol. 34
Provided that forestry Operations leave wide rides (the sun should penetrate to a quarter of the width of the ride-floor throughout the year) and that rides are designed to interconnect without creating wind-corridors, the sheltered pockets caused by felling blocks of timber and the disturbance associated with extraction and subsequent re-planting can create ideal conditions for a large number of insects. The nutrient enrichment often associated with tree growth on poor soils may itself encourage a wider diversity of plant species, in turn supporting a wider diversity of insect species. This is not to say that a reversion to nutrient-poor heathland is not a justified aim within the afforested areas, but to point out that there are other conservation and finance-positive ways of maintaining many of the insects typical of the Sandlings. Once again the overall aim is the breaking up of monocultures, be they trees, grasslands or heathers, into more varied species and structural mosaics. The April visits highlighted the importance of the frequent stands of blackthorn, Prunus spinosa, to the spring insect fauna. In the absence of frequent stands of sallow, Salix spp. this plant is the major available nectar and pollen source at this time of year. There is currently no lack of stands of this plant within the hedgerows of the area. However, widespread removal of hedges, or tidying up of forestry plantation rides, could have far reaching consequences. Hawthorn, Crataegus monogyna, played a similar role during the May Visits. The lack of other flowering plants, particularly ground flora, was a cause for concern at most sites during the spring Visits. Forestry rides again proved to have a richer flora than areas of open heath. One small area of Walberswick Common which was being regularly mowed was uncharacteristically rieh in flowers, suggesting that the lack of suitable grazing over the years may have impoverished the Sandlings considerably. The windy conditions at the Start of the May visits highlighted the role played by stands of scrub in providing shelter for foraging insects. Most of the species recorded at Blaxhall were found in the narrow corridor between woodland blocks at the north-eastern comer of the site. Such corridors with short Vegetation or areas of bare ground along tracks also form good nesting areas for aculeates. The Suffolk Sandlings have proved themselves to hold important populations of many species of bee and wasp, a group of insects which have been seriously affected by changes in agricultural practice over the past hundred years, and particularly the past fifty. Following the recognition of the importance of the Sandlings it is hoped that conservation management in the area will be able to take due note of the needs of this fascinating group of insects and ensure their continuity on the Sandlings Heaths. Mike Edwards B.Sc., F.R.E.S. Entomological Consultant Lea-Side Carron Lane Midhurst West Sussex GU29 9LB
Trans. Suffolk Nat. Soc. 34 (1998)
Plate 7: Bee-wolf wasp (Philanthus 1996 (p. 83).
triangulum
Fabricius) on Dunwich Heath,