The Macro-lepidoptera of Northumberland and Durham

During the period 1899-1913 J. E. Robson published the first, and up to the present time the only comprehensive survey of the lepidoptera of Northumberland and Durham. The time-lapse since the appearance of his Catalogue would be sufficient reason in itself to justify a revision of his work, but there are several other factors that suggest that a fresh review of the distribution and relative abundance of our local lepidoptera is now in order.

In the first place, changes in systematics have resulted in a new classification, and we now use that of Bradley and Fletcher (1979) based on the check-list of Kloet and Hincks published in 1972. Additionally, advances in taxonomy have resulted in the discovery of new species—in some cases rendering earlier records invalid (such instances are noted in the main text). Improvements in transport have increased access to the more remote areas of both counties, though the Cheviot massif, some stretches of moorland and more particularly the Border Forests remain under recorded. Coverage of lowland areas and in particular the coastline is now quite widespread however, thanks in no small measure to conservation work being undertaken on the initiative of the Nature Conservancy Council and the county Wildlife Trusts, which bodies have been most generous in granting rights of access to us for the purpose of compiling local check-lists. In addition a network of traps set up by the Rothamsted Experimental Station continuously monitor the lepidopterous fauna of a variety of habitats in both counties.

Though the trapping techniques of Robson's time are still used, the large Robinson MV trap run from the mains or a generator has greatly increased our knowledge of, in particular, some of the less common species, while the advent of the six watt Heath trap run from a twelve-volt battery has allowed investigation of hitherto inaccessible areas. A particular advantage of these traps over the older 'sugaring' techniques and collecting at street lamps is that they give a much clearer idea of the relative abundance of many species. Additional stimulus to recording has arisen through the formation of regional groups acting under the auspices of the Biological Records Centre at Monk's Wood, while the task of the amateur lepidopterist has been greatly eased by the publication of increasingly accurate and well illustrated identification guides by South (1961), Bradley, Tremewen and Smith (1973 & 1979), Skinner (1984), Goater (1985), et at. Correspondence with authors of the various volumes of The Moths and Butterflies of Great Britain and Ireland' (hereafter referred to as MBGBI) has further attempted to focus attention on the distribution of various critical species and groups.

Perhaps the most pressing reason for a new check-list is to attempt to chronicle the changes that appear to have taken place since Robson's day, and to correlate these changes where possible with changes in both local conditions and national distribution. Attempts to 'account for' distributional changes in terms of factors that may or may not be relevant is always a risky undertaking. It is our purpose here merely to draw the reader's attention to some points that we feel should be borne in mind when assessing such changes.

The most obvious factors requiring consideration concern changes in land utilisation, and here we would first mention the extensive planting of mainly coniferous forest, principally in upland areas, that has accelerated since the 1920"s, resulting in the disappearance of large areas of open moorland. Further inroads were made into this habitat during the 1939-46 war as a result of increasing agricultural requirements, and about this time also huge stretches of hedgerow began to disappear, to be replaced by environmentally sterile fencing. A less obvious but possibly even more drastic change was that of double and occasionally triple-cropping of hay meadows introduced from the late 1940's to satisfy the requirements of advances in silage production, a change that may have had dire consequences on the life-cycle of several species of moths and one or two butterflies. In view of these comments, it should come as no surprise that we have numerous changes to chronicle for the second half of the present century (though it should be noted that the recent pleasing development of restricting the mowing of roadside verges in some areas may be going some way towards improving the overall situation).

Changes due to climatic variation are somewhat more difficult to correlate in any meaningful way. Locally adverse conditions may cause a drastic drop in numbers in some species, but insect populations tend to be surprisingly resilient, and long-term effects are difficult to predict. There is one point that we feel worth drawing attention to, however, and that is that in the middle of our area, at the latitude of the Solway/Tyne gap, mainland Britain is at its narrowest east/west extension, and as a consequence the 'environmental gradient' between western (Oceanic) and eastern (verging on the Continental) climates (as shown for example by the rainfall gradient across the region) is quite steep. It seems possible, therefore, that slight climatic changes affecting our region could produce a critical situation for species already 'at risk', and that responses to such changes might more readily be observed in our area than elsewhere. Examination of the distribution maps in MBGBI Vols. 9 and 10 reveal at least 60 species, the distribution of which either reaches a limit or thins out critically in our region (possibly, as in the case of Acronicta megacephala (2278) leaving a disjunct population in north-central Scotland). By contrast, there is only one species, Photedes captiuncula (2344) that appears actually to prefer our region to others.

At present we would make no more of this situation than to suggest that changes in distribution that might be capable of correlation with climatic variation might be more readily evident in our areas than elsewhere. In case this should be correct, we have given as much detail as possible for those species whose numbers seem to be showing notable increases/decreases or which seem to be fluctuating markedly, so that the records for such species shall be as complete as possible. In view of the limitations of space, we have generally included maps only for those species where it would appear to us that there is evidence for some marked environmental limitation on distribution: species so rare that they can be adequately covered in the text have in general not been mapped, and neither have immigrant species unless in some cases the accumulation of records clearly indicates a preferred direction of immigration. Looking back over the 70—80 years that have passed since the publication of Robson's Catalogue, there are suggestions for several species that a marked and widespread northward extension of range took place during the period 1910—1930, that may have been connected with climatic variation. For many species, this was not adequately documented, but an example for which the record is fairly comprehensive has been quoted in some detail, namely Smerinthus ocellata (1980), as it shows how rapidly colonisation can occur under apparently favourable conditions. A comparable 'explosion' in population may at present be occurring in the case of Rhyacia simulans (2105), the progress of which should be closely followed.

Assessing relative increases/decreases in population really necessitates a continuous record, which for our region did not become possible until the advent of the Rothamsted traps, the first of which was set up at Kielder in 1959. The continuous records from this and other traps provide a wealth of information on dates of emergence and how they vary with weather, altitude, etc., relative abundance, number of cycles/year, possible correlations with environmental changes and other features. We have only referred to such information where it appears to be particularly significant, or differs appreciably from quoted data elsewhere.

In addition to the vast amount of information made available to us by the Rothamsted Experimental Station, and for which we now express our grateful thanks, we must acknowledge the great debt that we owe to other workers who have freely provided records, or whose check-lists we have drawn on. In particular we would mention the extensive records of George Bolam (1925), mainly from North Northumberland (vc 68), supported by W. G. Watson and R. Craigs working mainly in the North Tyne and Redesdale areas respectively in the first half of the century, when J. R. Johnson was active in the South Tyne/Derwent area, and J. P. Robson worked generally in the Barnard Castle district: but most of all, working throughout both counties (not to mention the farthest corners of the Scottish Isles as well) was without doubt J. W. (later Professor) Heslop Harrison - notable most particularly in our present context for his pioneering work on the critical identification and distribution of the genus Epirrita (Oporina).

F. W. Gardner obtained many valuable records using a Robinson trap in the mid-Tyne valley in the 1960"s and was followed into the next decade by Drs. B. and I. D. Wallace and then Dr. D. A. Sheppard and M. Eyre all of whom worked extensively in both counties. More recently, contributors become too numerous to mention, but we hope that acknowledgement of their records in the text will serve to indicate the debt that we owe them. Finally, we must acknowledge the sterling work by Dr. A. G. Long, ex-Deputy Director of the Hancock Museum who initiated the extensive set of record cards at the museum to which we have been allowed access, and to his successor, P. Davies, for continuing co-operation and the provision of the distribution map blanks - and last but by no means least our thanks go to D. Hall and his students at Sunderland Polytechnic who designed the cover for this book.

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