Worcestershire Record No. 21 April 2007 pp. 34-39

Geoff Trevis

The British list of hymenoptera contains around 6600 species distributed between three main groups, parasitica (parasitic wasps and ichneumons), symphyta (sawflies and wood wasps) and aculeata (bees, wasps and ants). The uncertainty about the number of species relates to taxonomic changes, for example the bumblebee Bombus lucorum has now been split into three species and the black garden ant Lasius niger has been split into two species L. niger and L .platythorax, and also to recent additions to the British list and to extinctions. The present survey relates only to the aculeate hymenoptera which comprise about 650 species.

The Biological Records Centre has records going back several decades but comparison of distributions between old and more recent records would yield little of value as recording until the last decade or so was sporadic at best. An arbitrary cut off of 1990 has been chosen as the basis for this review to provide data for future comparison. Similarly, there seemed little point in providing a large number of distribution maps as these would indicate only where recording has been undertaken and would, in most cases, reveal little of the distribution of the species concerned.

Indicating the status of species on the Worcestershire list has proved difficult owing to the number of different systems that have been published. We have the early system of RDB 1 to 3, RDBK, Na (Notable a), Nb (Notable b) etc. depending on the number of 10Km squares in which the species concerned has been found. There is a system available on the internet from JNCC which ranges from CR (Critically Endangered) to N (Nationally Notable). There is the system employed by MapMate software (which I use) which is very comprehensive ranging from Critically Endangered and possibly extinct to Universal. However, I finally opted for a simpler system used by the Bees, Wasps and Ants Recording Society (BWARS) in the latest edition of its handbook (2004), which is shown in table 1 below. All the records have thus been reclassified using this system though I have omitted “universal” as a category and all species not allocated another category will be covered by this.

Data have been obtained from the BRC and from my own database. These two sources provide a fairly comprehensive coverage but discrepancies have been found and until the two have been reconciled some uncertainty will remain. However, details of the rarer species appear to agree and it is only with commoner species that there are problems. Nonetheless, we have a total of 256 species equivalent to approximately 40% of the British list. Species richness is highest in the south-east of England, particularly on heaths in Sussex and Surrey, decreasing as one moves north-west. It is probable, therefore, that the Worcestershire total is a little low, bearing in mind the north-west range expansion of many species, and that further recording effort will reveal several new species.

The full list of species is shown in Appendix 1 along with the number of records for each species and the current status (see table 1 above). Table 2 shows the number of species in each category for Worcestershire.

Assigning a status to each species continues to be a somewhat speculative process as under-recording and genuine changes in species range and abundance will result in uncertainty. We know, for example, that the Bee Wolf Philanthus triangulum has shown a dramatic increase both in range and abundance. Similarly, both Nomada fucata and N. lathburiana have been found more widely in recent years and their status should probably be revised. Conversely, many bumblebees have been declining rapidly and species such as Bombus humilis and B. ruderarius may have their rarity status increased. There are one or two species on the BRC database that are of such rarity that I have omitted them from the list pending validation.

Clearly the apparent distribution of species is also influenced by many factors including actual distribution in appropriate habitats, recording effort (especially long term studies such as those undertaken by Michael Archer and Colin Plant on Devil’s Spittleful/Rifle Range and Hartelbury Common) and reporting bias. With regard to the last of these for example, we have more records of Hornets Vespa crabro than for Common Wasps Vespula vulgaris, presumably because people think that common wasps are so ubiquitous that they are not worth recording whilst Hornets are much more interesting and worth noting. Finally, until recently there have been few naturalists with the expertise to identify the aculeates with a reasonable level of certainty so that many records will reflect where these few people have collected rather than where the insects are. However, this is changing and as more recorders collect specimens and identify them, or send them for identification, we can anticipate a more even spread of data and hence more reliable estimates of distribution and abundance.

Species of note include Bombus ruderatus (a national BAP species) taken by Alan Baylis at Cherry Orchard (Worcester), by Martin Skirrow at Hanley Swan and by me near the Droitwich Canal. Indications nationally suggest that this species is showing an increasing distribution in contradistinction to many other bumblebees which, as noted above, include B. humilis and B. ruderarius. However, the first of these has been located at Cherry Orchard (Worcester) by Alan Baylis and at Kemerton Lakes by Harry Green and the second was found by myself at Wassell Wood. The changes in bumblebee status remain something of a mystery though habitat loss is undoubtedly involved whilst the effects of climate change are much less certain.

Among the other bees, the presence of the leaf cutter Megachile maritima at Cherry Orchard, (Worcester) was thought to be due to northerly spread up the Severn Valley from strong-holds in the sand dunes on the South Wales coast. However, further investigation revealed that it had previously been found by Michael Archer and Colin Plant on Devil’s Spittleful and Hartlebury Common and subsequently was also located at Habberley Valley. It may be, therefore, that it is a scarce though long time resident in appropriate sandy habitats in Worcestershire. Nonetheless, the cleptoparasite of M. maritima, Coelioxys conoidea, has been found only at Cherry Orchard and this may be a more recent immigrant.

The range of ant species in the county is low and undoubtedly many more of the commoner species have yet to be recorded. This is largely due to the behaviour of many ants which remain in cover under vegetation, leaf litter, bark etc. and can only be located by diligent searching. Among the rarities, Stenamma debile was found by Harry Green at Hayley Dingle (first thought to be Stenamma westwoodii) and Lasius brunneus is widespread. L. brunneus is of course particularly associated with the Severn and Thames valleys and is very rare elsewhere in the country.

Among wasps Kevin McGee has found the very rare pompilid (spider hunter) Anoplius caviventris. This is has been recorded in only 7 10K squares since 1970 but Worcestershire is more or less in the centre of the distribution and hence this species may be a rare native of the county. By contrast the some less rare, but nonetheless very uncommon, species such as Odynerus melanocephalus and Argogorytes fargei have shown, nationally, a distribution strongly biased to the south-east which suggests more recent spread into our county, possibly as a consequence of climate change.

A review of the best sites for hymenoptera revealed no surprises. Top of the list are the heathlands near Kidderminster which have been intensively studied for several years. This is in accordance with the national picture in which the top sites are the heaths of Surrey and Sussex. Kemerton Lakes too has proved a site of conservation importance for the hymenoptera. Here several visits have resulted in a good list and about 30 species were found in one day by Steven Falk. This site, at the base of Bredon Hill, has many features in common with the heaths in having large areas of bare, relatively friable soils for mining bees and wasps, a ready supply of nectar sources and brambles and scrub for the hole and aerial nesting species. Woods tend to be less rich though consistent recording effort, such as that by Harry Green at Tiddesley Wood and Rough Hill Orchard, and by the Wyre Forest Study Group surveys at the Roxel site and the orchards at Bowcastle Farm, can accumulate an impressive list. Woods generally favour wasps, as there is a ready supply of their prey, rather than the warmth loving, nectar feeding bees. Brown field sites can be of outstanding importance, as demonstrated by the survey at Cherry Orchard (Worcester) and brief visits to the old railway sidings at Honeybourne. Finally, gardens must not be forgotten as these often supply all the needs of aculeates, particularly bumblebees. Farmland, especially pasture, is relatively poor for most hymenoptera though, as we know, the yellow ant Lasius flavus, may be abundant. It will be interesting to see whether the new farm subsidies lead to more, wide field margins around arable fields and whether these lead to increased abundance of bees and wasps.

When collecting on farmland attention should be given to felled timber, especially if old, and to the root plates of fallen trees as these are attractive to many smaller hole nesting solitary bees and wasps. This was proved quite conclusively at Lodge Farm near Rochford. For most of the collecting day there I was finding only the common Andrenas and Lasioglossums but, towards the end of the visit an upturned tree was found whose root plate was in full sun. Here solitary wasps were abundant with several Ectemnius, Argogorytes and Chrysid wasps being located with a few seconds.

The vast majority of species have been caught with nets, generally by sweeping vegetation, and there have been few surveys using other methods. However, surveys undertaken by the Wyre Forest Study Group using Malaise traps have permitted some comparison. As a general rule, netting specimens results in a bias in favour of bees whilst Malaise traps collect more solitary wasps. Both systems are, therefore, necessary for a comprehensive site survey and careful searching at ground level and in vegetation should be undertaken if ants are to be included. It would be of great interest to see what other trapping methods, e.g. water traps, would produce. My only other information is from moth traps which seem particularly attractive to hornets.

Further collecting is necessary throughout the county if meaningful distributions are to be obtained. This applies particularly to common species such as common wasps, Vespula vulgaris, and German wasps, Vespula germanica which must be present in just about every monad. I am always pleased to receive specimens for identification provided full information is given i.e. site, grid reference, date and collector’s name.

It would also be of interest if potentially rich sites could be noted for later recording effort. These should be fairly open with patches of bare soil, there should also be herbs and shrubs as nectar sources through the year and some scrub and brambles for nesting sites. Sites will also be rich in flies and smaller spiders etc. which are the prey for many solitary wasps.

Finally, I would be very interested in further recording in old orchards. These seem relatively less attractive to bees than to wasps, as indicated by the Bowcastle Farm project. However, the results here may be due to the proximity of Wyre Forest and sites more isolated in farmland may show a different picture.