Shoreham Bank (Mill Hill)
Historic Notes
Extract from Colin Pratt's "History of the Butterflies and Moths of Sussex"

Shoreham Bank (Mill Hill) was nationally the most famous of all of the Sussex butterfly localities, yet its reputation was gained from just one phenomenon - the numbers and aberrations of the Chalk Hill Blue. The site's 20th century history has been mainly recorded by two giants of the net - R. M. Craske and A. E. Stafford.

The Chalk Hill Blue. that archetypal downland butterfly. has been nationally celebrated on the Bank since at least the 1820's (Stephens. 1828) - but. after a century and a half of tradition, I have seen more than one aged lepidopterist's eyes fill with tears when discussing the insect's modern history on those hills, now that even scientific collecting is technically banned. Despite the district's early reputation. during the late 19th century knowledge of Mill Hill became lost. The slope was then rediscovered by a close band of variety collectors in 1928, although its delights were then kept secret from most enthusiasts until 1955.

The cream of British variety-hunters collected at Shoreham Bank during its golden age. The following figures are known to have worked the slope from the late 1920's until the start of the Second World War - P. M. Bright and his chauffeur. A. A. W. Buckstone. V. r. Burkhardt, B. H. Crabtree, R. M. Craske and his brother J. C. B. Craske, Kirwin, F. A. Labouchere, C. G. Lipscomb- the Reverend J. N. Marcon. E. de Mornay- S. Morris, A. E. Stafford. J. Tetley. C. Wells. c. de Worms. and L. H. Bonaparte Wyse. Most devotees only visited once or twice a year but the dedicated worked the Bank all day and every day for at least three weeks - Stafford "collected & worked the slopes each day from 10-30 to 4 p.m. & sometimes later" - this often involving either daily travel by rail from London or the timing mid placing of annual holidays to coincide with the emergence of coridon. The highest number of enthusiasts to collect on the ground at any one time between the wars was 15. But in 1939 a sharp-eyed observer noted that "there were many collectors there every day & altogether about 20 have visited the ground, some for only a day or two days. others, practically the whole period" (Stafford. diary) - and even more were to be counted later.

Mill Hill certainly became by far the most intensively worked downland area in the county during the 1950's and it has been privately suggested by local conservationists that collating caused the decline of the Chalk Hill Blue here. This idea is ludicrous. The attraction of Shoreham's slopes was the occurrence of care aberrations which- by definition, only occur as a minute proportion of the local population. There were only about half a dozen really dedicated and obsessive collectors, and during favourable seasons they usually each took between one and three dozen butterflies after searching through around 100.000 insects. The most taken by one person in any year was 56 in 1945 by Stafford. the blues specialist (Stafford, diary). It can therefore be said with confidence that far less than 1% of coridon were ever killed by net and bottle - and, on average, in a worst case scenario, in my judgement the figure was about 0.2%. But the contribution that those hunters made to entomological science is immeasurable. with just part of their legacy lying in museums and reference books up and down the country.

Shoreham Bank faces west and was known as a delightfully scenic but breezy locality to work butterflies, where walks were "dusty and rather toilsome" during the 19th century (Arnold & Jeffrey. 1886). But even by the early 1920's, quarrying by cement-makers at Beeding was "eating like whitest leprosy into the hills. their fumes blackening the stun". Furthermore, it was also noticed that "Wide stretches of the downland which a year or two ago were free warren, are now so set about with wire that one might believe the eternal hills to have been made a dump for all that unwholesome material left over from the (first) war" (Allcroft, 1924). More importantly. as one early collector recalled, "there was little thorn on the hill, the turf was short and in May the whole place was absolutely yellow with the Horseshoe Vetch... The Down had a very large rabbit warren and in the evening a population of some hundreds of rabbits were all over that hill. These. I think kept the grass short there was no other means there except in certain years when there were two ponies" (R. M. Craske in Crane, 1972). Significant amounts of hawthorn were already present on the Bank by mid-century - by 1952 "much of the hillside" was "covered by soul)", and the overlooking road "used as a car lurk for picnic parties" (Dyson, 1953).

In 1950 most of the site was cordoned off with barbed wire. Later on during the same year Stafford waste that "the whole character of the ground has changed & it is obvious that many cows have been allowed to graze on it. The almost total absence of all flowers, the Scabious which was in profusion here was entirely absent except at the edge of the cornfield at the bottom of the hill. Also, the grass & even the Horseshoe Vetch & other plants were very sparse & the ground was almost bare of (any) vegetation at all, in fact. the bare earth was seen ......

Estimated numbers of Chalkhill Blues:

1937:   70,000
1945:   40,000    (RM Craske said 50,000 and my independent calculations came to 40,000)
1960:   20,000    (no evidence for this total, just surmise)
1970:  10,000    (speculative total)
1980:    6,000
1990 :   5,000
2000:    4,000
2010:    2,000  (without cattle grazing, with cattle grazing down to a 100)
2020:   Negligible

Shoreham Bank (Mill Hill) is the most nationally famous of the Sussex butterfly sites.

Photograph by Andy Horton
Chalkhill Blue (Photograph by Andy Horton)
Adonis Blue
Chalkhill Blue

This fame was created by the huge numbers and aberrations of the Chalkhill Blue Butterflies. The fame started from about 1820 when butterfly collecting became the vogue. During the heyday of butterfly collecting between the two World Wars, the private site was kept a secret by commercial collectors. In 1938 the area of Mill Hill and other downland was presented to the people of Shoreham, some 724 acres, although less than 28* acres remain as public open land. It was rediscovered in 1955. (*may be 30 acres).  It was rediscovered by butterfly enthusiasts in 1955.

Despite the large number of collectors, they did cause  the decline of butterflies on Mill Hill but the demise of the rabbit through myxomatosis and the invasion of scrub through the absence of the rabbit. This disease arrived in 1954, but in the cold winter of 1963, the hill was still devoid of scrub. The main invasion of woodland and scrub occurred since the new road was built in 1971, although ths scrub started before in the mid 1960s. 

Chalkhill Blue Butterfly femaleIn the 1950s (before my time) the area was fenced off and the upper slopes were grazed with cattle. The area was grazed right down and only Ragwort remained (like the fields adjoining nowadays). This seemed to have encouraged Hawthorn scrub, Dogwood and Creeping Thistles which remain today. The reports from butterfly collectors said that all the Horseshoe Vetch and wild flowers had been lost from the upper slopes. This remains the case in 2003, although there are now large swathes of longer grass and Scabious, Greater Knapweed, etc. The lower steeper slopes were fenced off and this is still a continuous mat of Horseshoe Vetch with incursions of Wild Privet

There is a report of a recovery after the cattle were removed and by 1960 there is an authentic report of 6000 Chalkhill Blue Butterflies seen on one day. In 1967 grazing was banned and this resulted by 1971 in a sudden growth of the long grasses, which are now forage harvested in late autumn. Volunteers than helped with scrub clearance but no lasting impression was made on the problem. In the late seventies, I still observed hundreds of Chalkhill Blue butterflies that had descended to the Waterworks Road where the grass was mown, but this area has been neglected and is now covered in nettles. 

Adonis Blues copulating with Horseshoe Vetch (Photograph by Andy Horton)

In 1990, cattle were again introduced to the upper slopes for a short period. The area looks very much like a lowland cattle pasture ten years later. Although the upper slopes now support large populations of many hundreds of Common Blues and Marbled Whites in the longer grasses, this seems to be at the expense of Chalkhill Blues. Erosion has been caused by hang-gliders and other human activities, but it appears that is not as great as the damage caused by cattle.

Horseshoe Vetch (Photograph by Andy Horton)

In 2003, my summer survey revealed that Horseshoe Vetch was still abundant on the lower slopes covering only about five acres, but that the same species on the middle and upper slopes is very small in area and does not support Chalkhill Blue Butterflies. Scrub incursions are very serious and a woodland has developed where there used to be bare hill. However, in the main breeding area on the lower slopes is still maintained although the scrub is making serious incursions, led by Wild Privet. The numbers of Chalkhill Blues seen on one day was 3000, which roughly corresponded to previous years, but this represents about one half of the number for 1960. Only one other day in 2003, I estimated the peak numbers at 2000. The only major management change in this time has been cattle grazing.

Records of Chalkhill Blues on Mill Hill

These are human observations and if the observers miss the date of emergence, the numbers will vary considerably.
My main criticism is the missing of the abundance in the late seventies (1977 or 1978) when I would conservatively* estimate the peak numbers to be in excess of 4000.
(*On the Waterworks Road there were over a thousand Chalkhill Blues on four different occasions whereas in 2003, the numbers in this location peaked at five.)

Altogether at least 25 species of butterflies have been positively been identified by myself in the last three years, and I expect this total to increase to 30 or more as this number have been found in the town of Shoreham including Mill Hill. In season the Chalkhill Blue still remains the most prevalent butterfly, with small population of Adonis Blues and slightly larger populations of Dingy Skippers, mostly on the lower short ward (20 mm to 35 mm) grassland. Large numbers of Common Blues and Marbled Whites are to be found on the upper slopes and these will most likely to be seen by casual visitors, although the dispersals of Chalkhill Blues will venture over the whole area in the search for nectar plants.

Mill Hill is now managed by the South Downs Conservation Board, who have taken over from the West Sussex County Council. 

Chalkhill and Common Blue Butterflies (Photograph by Andy Horton)Major reference:

A Revised History of the Butterflies and Moths of Sussex

Colin R Pratt
Publisher:  Booth Museum of Natural History 
CD-ROM  1999 

Mill Hill Wildlife Reports 2004

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