Mill Hill (June 2013)
Spring Downland Butterflies (May):
Adonis Blues (Photograph                    by Andy Horton)
Dingy Skipper                    (Photograph by Andy Horton)
Small Heath Butterfly
Grizzled Skipper
Adonis Blue Butterfly
Dingy Skipper
Small Heath Butterfly

Noticeable summer plants of the upper meadows include Greater Knapweed, Hardheads (=Lesser Knapweed), Field Scabious, Meadow Cranesbill, Alexanders, Pyramidal Orchids, Plantains, Melilots, Meadow Vetchling, Yarrow, Eyebrights, Musk Thistles, Hounds-tongue*, Perforate St. John's Wort*, Great Mullein* and many others. Herb Robert is found amongst the scrub.
(*notably on disturbed ground.)

Some Indicator Plants of Ancient Downland

Horseshoe Vetch (Photograph by Andy Horton)
Autumn Gentian
Horseshoe Vetch
Common Milkwort
Dog Violet
Autumn Gentian

Other indicators on the lower slopes include Dropwort, Autumn Ladies Tresses (upper plateau), Hairy Violet, all of which are rarely found on pastures, restored wildlife meadows or agricultural downland. Other downland plants that are more likely on the biodiverse down herbland are Wild Thyme, Carline Thistle, Dwarf Thistle, Squinancywort, Fairy Flax, Small Scabious, Common Centaury and Wild Basil. There are other more widespread wild plants like the Mouse-eared Hawkweed, Rough Hawkbit, Lesser Hawkbit, Bird's Foot Trefoil, Ground Ivy, Germander Speedwell, Field Speedwell, Sweet Violet, Self-heal and Yellow Wort.
Wild Flora and Fauna on Chalk   flickr
Adur Wild Flowers 2009


A large part (724 acres) of the downs including Mill Hill were presented to the people of Shoreham in 1937

Lower Slopes of Mill Hill, May 2006 

Just over 30 acres still remain as public open land and a Local Nature Reserve.  This is divided into about 11 acres of grassland and meadows above the ridge, about 9 acres of scrub, the copse and glades at the northern end, and about half of the prime Chalkhill Blue area of 6.4 acres of herbland remaining. 6 acres has been lost to a Sycamore woodland on the southern slopes. 

This is low fertility chalkland not suitable for grazing. The top area is effectively a wild meadow and the lower slopes a rabbit warren dominated by prostrate (not the upright form) Horseshoe Vetch, Hippocrepis comosa

Link to                            the Mill Hill web page for 2009

Horseshoe Vetch

Chalkhill Blues:

Mill Hill is nationally important because of its population of Chalkhill Blue Butterflies. Estimates of the numbers are notoriously inaccurate. In the 1950s the population was estimated by R. M. Craske to be 50,000. This may be an exceptionally good year. I would estimate the numbers at that time to be nearer 25,000 for Mill Hill only. After the cattle grazing and thorn incursions the numbers plummeted to the most reliable estimate in 1960 of 6,000. The new road and Sycamore woodland further denuded the Horseshoe Vetch, Hippocrepis comosa, and bare chalk downland to a figure I have estimated at a top figure of 3,000 Chalkhill Blue Butterflies at the turn of the millennium (counted in 2003). Almost all these butterflies are now to be found on the six acres of the lower slopes.
Graham Hart in the 1990s estimated the numbers at 6,000. This is not out of the question and this would accord with the R. M. Craske estimate of 50,000. This would be the maximum population density that could be expected on the carpets of Horseshoe Vetch (based on German figures).
Protection of the current population requires man management of the scrub incursions, which means removal of the Privet

Text by Andy Horton Calcareous Grassland Message
"Our family lived at The Mill House, Mill Hill, from around 1933 until about 1967, and every July we saw the "Butterfly Men" walking past onto the Downs. My father used to tell us that they were interested in the blue butterflies."
Heather Clark (née Eager), Ryde, Isle of Wight
Nearest Postcode:  BN43 5FH
Grid Ref:  TQ 21170 07444  (upper car park)
Geographic Link      OS Map
Google Earth Map
Magic Map of Mill Hill NR
Local Nature Reserve Designation
Natural England: Local Nature Reserves
Multi-Map (Bird's Eye View)
Grid Reference Finder

Threats to the Butterfly Downland site at Mill Hill
The butterfly lower slopes at Mill Hill are under serious threat by a natural process known as ecological succession where the woody shrubs like Privet, Brambles and Hawthorn invade the herb-rich slopes gradually turning the downs into woodland and eliminating the butterfly larval food plants especially the Horseshoe Vetch, Hippocrepis comosa, on which the Chalkhill Blue Butterflies rely. The remedy is by expert professional removal of the Privet on a regular basis. This job is now being undertaken by volunteers. 


Mill Hill on

Mill Hill on



   Footpaths at Mill Hill


30 May 2019

Yellow Belle Moth, Aspitates ochrearia, Dogwood, Dropwort
Tatty Adonis Blue with Horseshoe Vetch seed pods

On a Fresh Breeze (Force 5) afternoon, about forty Adonis Blues fluttered around the lower slopes of Mill Hill, with a few male Common Blues, with occasional Brimstone Butterflies on patrol, frequent 20+ Small Heaths, a Cinnabar Moth, and a Yellow Belle Moth, Aspitates ochrearia. Some of the Adonis Blues were as tatty as the fading Horseshoe Vetch. No skippers were searched out. There was a Speckled Wood amongst the scrub. On the top of the hill, the first Greater Knapweed was in flower.
Adur Moths 2019

Dogwood is rarely allowed to grow into a small tree. Interesting fact: in the sun the twigs are coloured crimson, while those in the shade are lime green.
Woodland Trust Information
21 May 2019

Adonis Blues
Grizzled Skipper

White fluffy Cumulus clouds allowed intermittent sunshine brought frequent butterflies out on the lower slopes of Mill Hill. About three quarters were lively Adonis Blues (38+7=45 in the transect acre, more over the slopes) over the swathes of Horseshoe Vetch, Hippocrepis comosa, frequent Small Heaths (20+), patrolling Brimstone Butterflies (10+), a few Large Whites, a fresh Grizzled Skipper, a fresh Dingy Skipper, a Wall Brown (on the southern steps), a very fast flying Peacock Butterfly, at least two each of Burnet Companion Moths, Cinnabar Moths and Treble-bar Moths. Two pairs of Adonis Blues were mating. Grasshoppers were stridulating at the northern end of the lower slopes and small movements were thought to be nymphs. Wild Mignonette was in flower. The first Dropwort appeared on its tall stalk above the short green vegetation.

Wild Mignonette, Dropwort, Hounds-tongue
Horseshoe Vetch & Milkwort, Bladder Campion

I noted the meadow north of the upper car park was now covered in Brambles and the vegetation already up to chest height. I did not venture in as it was getting late in the afternoon. The middle slopes immediately south of the Copse had patches of Horseshoe Vetch and the first Bladder Campion was just about flowering. Crosswort was recorded for the first time (it is easily overlooked) on Mill Hill. Hawthorn was beginning to lose its blossom as Elderflower was beginning.

20 May 2019
Rain curtailed my early afternoon visit, on a day not bright enough to make the butterflies active, although I disturbed five male Adonis Blues, one Brimstone Butterfly, and a Cinnabar Moth in a leisurely fifteen minute of less than half the one acre transect on the lower slopes.

Rough Hawkbit, Silverweed
Hairy Violet, Bulbous Buttercup

I noted the following wild flowers for the first time this year: Rough Hawkbit, Mouse-eared Hawkweed, Hairy Violet, Dog Rose and the first flowering on Mill Hill of the large shrubby Hounds-tongue. The smaller than usual amount of flowering Horseshoe Vetch, Hippocrepis comosa, was disappointing, with none around the Tor Grass, which appears to have spread.

13 May 2019

Common Blue, Treble-bar Moth, Adonis Blue
Brown Argus, Speckled Wood, Adonis Blue
Adonis Blue,  Adonis Blue. Dingy Skipper

On a sunny afternoon on the lower slopes of Mill Hill produced scores of restless butterflies fluttering around the early swathes of Horseshoe Vetch, Hippocrepis comosa, There were well over a hundred per acre of nine species and all of them were very active and I had to wait for over an hour for any to settle nearby. Dingy Skippers were the most frequent with over forty seen, but Grizzled Skippers were old and much harder to find only a handful including an amorous or sparring pair. The only one that settled for a second was slightly frayed at the edges. Twenty or so male Adonis Blues were very lively until they came across a few females. Small Heaths (12+) were frequently seen often chasing each other and sparring with other species including occasional Common Blues. Brimstone Butterflies patrolled incessantly without pausing, occasionally bumping into the whiter females and both a Large White and a Green-veined White. A flash of grey was a disturbed Treble-bar Moth, and a pretty Mother Shipton Moth was recognised when it settled. A Speckled Wood patrolled the southern steps and a fresh Brown Argus was seen clearly by the winding path, near some Wayfaring Tree shrubs.
Nine butterfly species and two macro moths


Hawthorn was flowering all over Mill Hill on some small trees at its peak blossom. On the top, south of the reservoir, the thick stems of Knapweed Broomrape appeared. This is a large parasitic plant. Nearby, the Cowslip patch was nearing the end of its flowering period. I also noted some Bird's Foot Trefoil with its small yellow flowers. On the lower slopes there were Dog Violets and clumps of Milkwort amongst the Horseshoe Vetch.

2 May 2019

Dingy Skipper with Horseshoe Vetch, Hippocrepis comosa

A flutter of brilliant blue over the lower slopes of Mill Hill heralded the beginning of summer on the downs with the first male Adonis Blue Butterfly of the year. It was unmistakable even though seen in the middle distance for 15 seconds at most; too far away to follow it for a photograph. Under a dark cloudy sky with the first spots of rain, it was too cool for many butterflies. It was only after nearly an hour did I manage to disturb the first of half a dozen Dingy Skippers, followed soon after by a Small Heath, a Green-veined White and a probable Peacock Butterfly. If I had not delayed my return I would missed the Adonis Blue and a probable Wall Brown. A Cinnabar Moth was seen clearly but it quickly disappeared into shelter. Crane-flies were mating. And the green beetle on Bulbous Buttercup seems to be Cryptocephalus aureolus.  The small green grasshopper nymphs frequently seen on the lower slopes of Mill Hill were probably the Common Green Grasshopper, Omocestus viridulus. A small Holly Tree appeared amongst the undergrowth on the disturbed ground.
Floral Gallery

24 April 2019

Horseshoe Vetch, Cowslips, Milkwort, Ant Myrmica sabuleti
Dog Violets, Hawthorn, Dandelion

Predictably, the butterflies did not show on the lower slopes of Mill Hill, with a chill (air temperature 12° C) on the breeze (Force 6 gusting to Gale Force 7) and intermittent April showers. A Speckled Wood made a flight near the southern steps, at the last knockings, as I headed for home in light rain. Wayfaring Tree was beginning to flower.
Adur Hoverflies

Ant, Myrmica sabuleti

23 April 2019
With the first Horseshoe Vetch, Hippocrepis comosa, appearing in bud on the lower slopes of Mill Hill, more butterflies were seen than expected on as hazy afternoon (air temperature 16° C).

A variety of ten butterfly species was more apparent than sheer numbers with Speckled Wood (one on the southern steps), Brimstone 3+, Small White 1+, the first of the year Small Tortoiseshell (southern, top), the first of the year pair of Dingy Skippers, 2+ Grizzled Skippers, 1+ male Orange Tips, another first of the year fresh Small Copper, at least one Peacock Butterfly, occasional Small Heaths 4+, and two Treble-bar Moths. Micro moths were frequently seen and ones recognised were the pyralids Pyrausta purpuralis and Pyrausta despicata as well as an even smaller Pancalia. A small bee was occasionally seen, small and rather distinctive in yellow and black barring: I think this was a Nomada species, most likely Nomada goodeniana.  Very small bright green grasshopper nymphs were seen amongst the dense green undergrowth.
Adur Butterfly List 2019

There was one large (25 cm with a truncated tail) Slow Worm, south of the Reservoir.

18 April 2019
Plenty of butterflies out in the warm sun on Mill Hill this afternoon: at least five male Orange Tips, loads of Brimstone and Peacock, couple of Small Tortoiseshell and a single Green Veined White. Possible Grizzled Skipper but only a fleeting glimpse. Bird wise, Whitethroats and Blackcaps were there, along with the Chiff Chaffs. A few Swallows were passing through.

Report by Nick Carpmael on Mill Hill Nature Reserve  facebook

17 April 2019
I disturbed a single Skylark from the plateau of Mill Hill on a hazy afternoon. It took flight after I thought I heard it singing earlier, but there were House Sparrows (? ID) singing melodiously for a mate from the scrub, and it was too hazy to see a lark in the blue sky. Cowslips were flowering by some rabbit burrows (disused) on the middle open part of Mill Hill west of the top copse.

Ploughman's Spikenard (dead), Speckled Wood
Grizzled Skipper, Milkwort with Pill Bug

On the middle of the lower slopes I spotted just a single Grizzled Skipper, followed by the small pyralid moth Pyrausta nigrata, and later a Small White Butterfly and a strong flying Peacock Butterfly, and on my return journey a Speckled Wood fluttered around the southern steps. Dog Violets were now abundant but there still seemed to be less scattered over the slopes than in previous years. Milkwort were poking out of the short vegetation. I noted the top leaves were much longer than the leaves at the rosette base. This is typical of the local Milkworts which I have identified as Common Milkwort Polygala vulgaris in previous years, but this has not been confirmed.  Occasional spiders were spotted crawling rapidly over the undergrowth, mostly very small Wolf Spiders, Pardosa, but also a full sized Nursery Spider and a tiny pale Crab Spider.
Adur Milkworts

11 April 2019
On a afternoon when the sun came out unexpectedly, I quickly spotted my first two Grizzled Skippers of the year on the lower slopes of Mill Hill, now decorated with Dog Violets, but much more sparsely than normal. A Common Bee-fly hovered above the violets and a Carder Bee flitted between the flowers quicker than my camera could focus. My first Brimstone Butterfly of the year fluttered past. The first of three Peacock Butterflies landed intermittently. No more skippers were seen.
Adur Butterfly List 2019

Caterpillars of the Adonis Blue Butterfly* with attendant Red Ants
(*these could be a Chalkhill Blue caterpillars)

Most of the observed action occurred amongst the dense interlocking leaves on the lower slopes where a brigade of working mutualistic red ants, Myrmica sabuleti, were attracted by sugary secretions of the green and yellow caterpillars of the Adonis Blue Butterfly. The ants are meant to protect the caterpillars (some were fourth instar) and pupa from predation. Ben Greenway helped me find the caterpillars, but I found one for myself by following the ants activity.

"The larvae are green with yellow stripes running along the length of the body. Unlike its close relative, the Chalkhill Blue, the larva of the Adonis Blue feeds by day. The larva has a Newcomer's gland in the 7th segment which provides secretions that are attractive to ants. This is a symbiotic relationship for, like many other blues, the Adonis Blue larva (and pupa) is afforded protection by the ants from parasites and other predators.
Early instars feed by grazing on one side of the leaf, leaving the epidermis of the other side intact. When not feeding, the larva rests at the base of the food plant, often on bare soil. Ants are known to bury the larva in a cell in the earth, where the ants continue to "milk" it for secretions. If not over wintering, this stage lasts around a month."
The primary larval food plant is Horseshoe Vetch, Hippocrepis comosa.
Adonis Blue Life Cycle (UK Butterflies)

A small Wolf Spider, Pardosa, crawled amongst the undergrowth. The upright dead bronze and silver dead Carline Thistle plants were quite noticeable on the lower slopes, as expected.


Amongst the scrub on the upper part of Mill Hill, the white blossom of Blackthorn looked attractive against the blue sky. There were a few Cowslips south of the Reservoir (the only upper part of Mill Hill visited.)

30 March 2019
I stopped in at Mill Hill and managed to find a Grizzled Skipper, the first of the year reported in Sussex.

Report by Jonathan Crawford on Sussex Butterflies
Adur Skippers

19 March 2019

Wind-blown Hawthorn above the Ridge

On a dull afternoon I made my first cursory visit of the year (after a week of squalls) to Mill Hill, just to the area around the Reservoir. A hundred mixed gulls filled the cloudy sky. There were Sweet Violets scattered sparsely over the undulating area immediately south of the Reservoir. Clumps of Daffodils were still showing. Even the small birds flying between the bare branches of Hawthorn were hard to discern as it was so dark. Some of the paths were muddy but there was no standing water seen.



Mill Hill Wildlife Reports 2018 (Link)

Mill Hill Wildlife Reports 2016 (Link)
Mill Hill Wildlife Reports 2015 (Link)
Mill Hill Wildlife Reports 2014 (Link)
Mill Hill Wildlife Reports 2013 (Link)
Mill Hill Wildlife Reports 2012 (Link)
Mill Hill Wildlife Reports 2011 (Link)

Adur Valley & Downs on facebook

Identification of Grasses (Link)
Mill Hill Grasses

A Nature Reserve is defined in Section 15 of the National Parks and Access to the Countryside Act 1949, as land managed for the purpose:

(a) of providing, under suitable conditions and control, special opportunities for the study of, and research into, matters relating to the flora and fauna of Great Britain and the physical conditions in which they live, and for the study of geological and physiographical features of special interest in the area; or
(b) of preserving flora, fauna, or geological or physiographical features of special interest in the area; or for both these purposes.

(Estimated numbers for Mill Hill Nature Reserve only are in brackets)

Chalkhill Blue (3000 +)
Adonis Blue (50 -100)
Dingy Skipper  (75)
Small Heath (250)
Wall Brown  (12)
Meadow Brown  (300)
Marbled White  (50)
Gatekeeper   (200)
Speckled Wood  (>50)
Green-veined White (2+)
Common Blue  (>4000+)
Small Blue       (5)
Brimstone        (8)
Small Skipper   (>50)
Large Skipper   (10+)
Grizzled Skipper  (20)
Brown Argus   (>30)
Green Hairstreak ( a few)

The other species may breed on Mill Hill, but there main breeding area will be adjoining fields or slightly further away. e.g. Small Blue (included above), Small Copper, Small Tortoiseshell, Green-veined White, Peacock, Ringlet, Small White, Large White, Comma, Holly Blue, Orange Tip. (=10). There are huge variances each year for most species.

The following are immigrants &/or hibernators:  Red Admiral, Painted Lady, Clouded Yellow.

The following have not been positively identified (because of ID difficulties):  Essex Skipper. This species is now included for a local field on the Adur Levels within 500 metres of Mill Hill.


The following was confirmed only in 2009: Green Hairstreak.

The following was confirmed only in 2014: Dark Green Fritillary

The next one is no longer found on Mill Hill but were there in the distant (1947) past: Grayling.
The next one has been recorded near Mill Hill in the middle distance past:  White-letter Hairstreak


The Silver-spotted Skipper does not appear to ever have occurred on Mill Hill
The Silver-studded Blue has never been recorded from Mill Hill

The Short-tailed Blue was recorded as a single immigrant in 1956.

17 August 2009
A possible (unconfirmed) Brown Hairstreak Butterfly was spotted. A confirmed one was spotted nearby.

Brown Hairstreak and Silver-spotted Skipper have been confirmed from Mill Hill. The first is notoriously difficult to spot and was probably already there. The skipper may be a new addition, but it is small and not easy to spot, and there have now been numerous sightings

Adur Butterfly Page


History of Mill Hill

Aerial Map
Lower Adur Levels (MultiMap) including Lancing Clump and Mill Hill

Horseshoe Vetch, Hippocrepis comosa
First Draft of the Article for the Shoreham Society Newsletter

Link to the            Adur 2012 Nature Notes pagesLink to the Adur Nature Notes 2011            web pages

Link to            the Adur 2010 Nature Notes pagesLink to the Adur Nature Notes 2009            web pagesLink to the            Adur Nature Notes 2008 web pagesLink to the Adur Nature Notes 2007            web pages
Link to Adur            Valley Nature Notes 2003Link to the Adur Nature Notes            2004 Index pageLink to Adur Nature Notes 2005 Index pageLink to the Adur Nature Notes 2006            web pages