Worcestershire Record No. 2 April 1997 p. 6

THE HYMENOPTERA

The Hymenoptera is a huge group comprising a large percentage of the total insect population of Great Britain (about 6,500 species out of about 23,000 species of insect). Defining what is meant by "hymenoptera" is not easy and perhaps the most comprehensive if unintelligible definition I have come across is "The hymenoptera are haplo-diploid, holometabolous insects which have biting mouth parts, but which lack elytra". Certainly these are matters which we will all be able to check out in the field! They are, of course, the bees, wasps, ants, sawflies and wood wasps, which share the observable features of biting mouthparts; two pairs of membranous wings, the larger forewings and the smaller hind wings linked by one or more small hooks; female ovipositor generally present; and antennae prominent, generally with n@me or more segments.

There are about 6,500 species of hymenoptera recorded in Great Britain which range from the well known social wasps and bees to obscure parasitic species recorded perhaps only once by an academic expert in the field, and who is probably the only person in the country who could identify the insect. The first stage of their classification is into two groups, the symphyta and the apocrita. The symphyta are the sawflies and wood wasps and the apocrita are the species having the typical "wasp waist". The apocrita are again subdivided into two groups, the parasitica and the aculeata. As their name suggests the parasitica are species which have adopted a variety of parasitic ways of life, the majority of them being so little studied as to be virtually unknown. The aculeata are the species in which the female ovipositor has been modified to form a sting and which include the familiar social bees and wasps. At the latest count, the symphyta comprise about 470 species, the parasitica about 5,500 species and the aculeata some 74 species of social bees, ants and wasps, about 217 species of solitary wasp and about 226 species of solitary bees (Archer, 1996).

The present status of the Hymenoptera generally is probably largely unknown. Archer notes 125 Red Data Book species (53 solitary wasps and 72 solitary bees), of which 31 may well be already extinct, plus a further 91 species designated nationally scarce. The Red Data Book also records two endangered wood ants, Formica pratensis and Formica transkaucasica. A further source of information is "Biodiversity: The U.K. Steering Group Report". On the short list are three ants, Formica candica (transkaucasica), Formica exsecta and Formica pratensis plus the Shrill Carder Bee, Bombus sylvarum. The middle list adds one ant, Formica rufibarbis and nine bees - Andrena floricola, Andrena gravida, Andrena lathyri, Andrena lepida, Bombus distinguendus, Bombus humilis, Bombus ruderatus, Bombus subterraneus and Osmia xanthomalana. Finally, the long list includes the bees Anthophora retusa, Colletes cunicularis, Lasioglossum angusticeps, Lasioglossum pauperatum, Lasioglossum sexnotatum, Nomada errans, Nomada sexfasciata, Osmia inermis and Psithyrus rupestris plus the wasps Chrysis pseudobrevitarsis, Crossocerus vagabundus, Homonotus sanguinolentus, Miscophus ater, Odynerus simillimus, Pemphredon enslini and Pseudopipona herrichii. However, considering the number of species in Britain the above list probably represents and underestimate.

When it comes to the parasitic wasps the situation is hopeless and the Red Data Book lists no species at all. It comments: "Although accounting for about a quarter of our insect fauna, the parasitic Hymenoptera are among the least understood insects in Britain and, at a time when the ecology - and indeed taxonomy - of so many remains obscure, it is difficult to single out the species and groups whose populations are most at risk" and "Many parasitic Hymenoptera have been collected on only one or two occasions in Britain but, in view of our ignorance of their origins and host associations and the paucity of collectors, it is probably advisable to ignore all these as candidate species until ecological knowledge enables surveys to made with respect to their host populations".

Why are the solitary species under threat? Five major reasons have been listed by Else, Felton and Stubbs (1978):

1. Solitary bees have a low reproductive rate of about 8-12 per generation with many producing only one generation per year.
2. Each species has a complex mixture of resource requirements e.g. bare dry soil or dead wood in a sunny sheltered situation for nesting and a nearby habitat with flowers for food and prey.
3. As traditional countryside disappears, species have become increasingly restricted to habitats which are not undergoing intensive agriculture. Unfortunately, these habitats are being lost.
4. Most species have limited powers of dispersal so that, as suitable habitats become fragmented, re-colonisation of isolated patches becomes less likely.
5. Many species require sunny, sheltered, bare ground or dead wood for nesting, which is usually found in disturbed and neglected habitats e.g. crumbling soft rock cliffs, eroding river banks, disused quarries, bramble patches and lying or vertical dead wood. The growth of vegetation, stabilisation of river banks and the tidying-up and removal of bramble and dead wood eliminates these habitats.

Robinson (1997) provides an interesting illustration of how a common but varied habitat can provide for these insects. A study in his garden, which he describes as "20 years old, on a modern estate and of typical suburban lay-out", found six species of bumble bee, one cuckoo bee and thirteen species of solitary bee. The garden is in a village surrounded by permanent pasture. The report goes on "The attraction of the garden is clearly as a pollen and nectar source. In this respect Natland stands out as an island of floristic diversity in a uniformly green landscape, thin hedges and stone walls. The only other places of any value for solitary bees which I have been able to discover in the vicinity are a few stretches of roadside verge and some slopes beside the river which are too steep for the farmer to improve".

In the Worcestershire Biological Record Centre the hymenoptera records are few and far between except for the systematic work of Dr Michael Archer, mainly at Devil's Spittleful and Rifle Range. Dr. Archer has been visiting regularly from the University College of Ripon & York St John to record the solitary bees and wasps. His latest report of visits made in July and August 1996 says "I have been able to add a further six species to give an unofficial list of 121 species". This is an impressive total which underlines the importance of heathland habitat for many species of the group. An interesting task, with Michael Archer's permission, would be to analyse the data using his quality and species quality methods.

There is a great deal of work to be done on recording Worcestershire's Hymenoptera and any information on the group as a whole will be welcome. Even common species of social bees and wasps are virtually unrecorded so that a little effort with these will pay dividends. Perhaps one day we can arrange an introductory course on identification and start a local recording group. Nationally there is a Bees, Wasps and Ants Group and it would be a great step forward if we could begin to contribute to its work and gain insight into the status of these fascinating insects in our county.

References

Falk, S (1991) A review of the scarce and threatened bees, wasps and ants of Great Britain. Research & survey in nature conservation no. 35. Nature Conservancy Council, Peterborough.