The Butterflies of Battlesbury Hill Fort 19th May 2018

A Saturday in May and the welcome sun and warmth was very much in evidence again as Peter and myself set off with a lightness of spirit that only the prospect of daylong sunshine can bring.

Peter had read on the Butterfly Conservation site that good numbers of Marsh Fritillarys and Duke of Burgundy butterflies, both of which are now very rare, had been seen at an Iron Age Hill Fort near Warminster in Wiltshire, on the previous Thursday or Friday.

Battlesbury Hill Fort was constructed about 2500 years ago and is now owned and managed by Defence Estates. The hill on which the fort is constructed is situated at the edge of a ridge of chalk downland extending 30 kilometres eastwards, and dominates the surrounding countryside looking down on one side to a large army camp and the town of Warminster  and on the opposite side across a wide area of farmland and the western edge of Salisbury Plain military training area. The hill fort is huge and the defences follow the natural contours of the hill and so steep is it in places that it is virtually inaccessible on the north and northeast sides. It has mostly triple ditches and ramparts  but only double on the southeast side. In size it is about 23.5 acres in extent.

Views from the top of the hill fort

After a long drive through a succession of pleasant rural Wiltshire villages and a few frustrations with the Satnav in Warminster we finally ascended a road, climbing steadily uphill, with Army training barracks and grounds, all heavily fortified with high fences, on both sides of the road. At the top of the hill we found a dusty layby and the entrance to the bridleway that gives access to the hill fort and we parked the car here.

Another walk of half a mile uphill on the bridleway took us through chalk grassland, eventually bringing us to the entrance gate to the fort, complete with warnings from The Army about the dangers of ordnance lying about in areas they use for training and another sign board with a brief synopsis about Battlesbury Hill Fort

We carried on through the gate into the remains of the fort and then were faced with a conundrum. Just which of  the many chalk  tracks should we follow over this large and somewhat daunting area?We really had no idea.

We split up and Peter took a higher track while I decided on a lower one and we duly set off in our respective directions. 

The lower chalk track that I went down

I really had no clue where to look and for the first few minutes was at a complete loss but leaving the track and walking part way up a steep bank to my left I disturbed a Green Hairstreak from a small hawthorn bush. It flew around wildly, looking brown rather than green in flight but when it settled and closed its wings the beautiful emerald green colouring on the underwings was all too evident. It became obvious that this hawthorn was its territory as it regularly flew around when disturbed by other insects but invariably returned to the same bush and often the same leaf. I also found a Cinnabar Moth which clumsily crash landed in the grass, spreading its wings wide to reveal the very smart black and red markings on its upperwings and all red hindwings.

Green Hairstreak

Cinnabar Moth

I called Peter to learn he had not had much luck so we joined up and took the highest track heading vaguely southwestwards and running along the top of the highest rampart. 

The highest track circumventing the top of the fort

There was a stiff but warm breeze blowing but as we progressed the wind was less obtrusive and it became quite warm. The main feature of  the track was the regular appearance of Wall Browns, a butterfly I have not seen for some time, warming themselves on the white sun baked chalk of the track. On landing ahead of us they always immediately closed their wings, forming a distinctive little dark triangle on the chalk until disturbed once more by our progress.

Wall Brown

Eventually we left this track and descended onto a warm but steep bank of grass and downland flowers that dropped down to the  topmost defensive ditch of the fort. 

The steep bank and ditch where we first encountered the
Marsh Fritillarys

It soon became apparent that this sunny, warm and sheltered south facing area was very much favoured by the butterfly we most wanted to encounter. Marsh Fritillary. Peter called to me that he had found one and for the next half an hour both of us regularly encountered this most beautiful of fritillarys, perching on the downland grasses and flowers. The patterning on their wings is exquisite and all of them seemed to be in virtually pristine condition, presumably having just hatched. The wings are a pleasing lattice work of chequering, much like a stained glass window, consisting of irregular buff and orange squares outlined in black. In all we estimated we must have seen in excess of thirty,  cruising and fluttering over the grass, and like us making the most of this sunny and warm day. 

Marsh Fritillary

There were other butterflies sharing the bank with them too. A Small Copper, as ever feisty and brooking no interference regularly tussled with any passing Marsh Fritillary, much to our frustration, as time and again just as we were going to get that particular shot of the fritillary, the Small Copper drove it off but eventually we got our images and all was well with the world again.

Small Copper

Dingy Skippers also put in brief appearances as did a very tatty Small Tortoiseshell, some Large Whites and the occasional Brimstone and Orange Tip as well as a day flying moth called Mother Shipton. 

Mother Shipton moth

A very small butterfly caught my eye, flying amongst the short grass and on landing it perched with wings firmly closed and showing as pale greyish blue stippled with black and orange spots. It was superficially similar to a blue butterfly but was too small. It could only be one thing, a Brown Argus and on opening its wings to the sunshine it confirmed its identity by showing off its chocolate brown wings bordered with bright orange spots.

Brown Argus

We ascended back up the bank and continued on the track this time encountering a Small Heath and then a mating pair of Wall Browns. Initially I was a little confused, as what I at first thought was a single butterfly flopped heavily away from me, but then I could see there was a male, attached rear end to rear end and being carried by the larger female. She could not fly far like this and they soon flopped into the dry grass to lay on their sides as the mating process continued.

Wall Browns mating.The larger one is the female

Marsh Fritillarys glided to and fro, always bringing that air of excitement as they passed by and eventually we came to a stop where our track was crossed by another and decided to return via the next track down that ran parallel on the further edge of the ditch between. Dingy Skippers and two more Green Hairstreaks flew around randomly by the edge of the track, the Green Hairstreaks looking worn, with slight tears to their wings. We came to another sun warmed area of short grass and  butter yellow Horseshoe Vetch and a male blue butterfly flew up. Not any blue but a vivid electric blue, the blue of tropical sea over sand, absolutely stunning from certain angles. It was an Adonis Blue perhaps the most beautifully and intensely coloured of any of the blue family. It was joined by two more, all of them keeping to this particular area of barely grassed chalk and short flowers, tussling occasionally with each other but soon separating and nectaring on the profusion of tightly clustered yellow vetch flowers. Reluctantly we left them and walked on back towards where we had started in what seemed hours ago in the morning. 

Adonis Blue

It was now getting hot as the middle of the day was upon us and we came to a large area of grassed slope on the southern side dropping away steeply some hundred feet downwards.This area was alive with Marsh Fritillarys and two butterfly enthusiasts were calling out to each other 'There's one', 'There's another' to each other as they wandered along half way down the bank.We found more fritillarys up on a level with us. It is impossible to be accurate but I calculated we had seen at least a hundred  Marsh Fritillarys along this bank and the bank where we had been earlier. It was surely no coincidence that these banks were the sunniest and most sheltered.

We got to the end of the track, where we had first started in the morning and stopped to have a rest.Then I suggested to Peter that we take the lowest track around the fort, heading westwards, the same track that I had commenced to walk when we first arrived here. It was downhill and ran though scattered small hawthorns and classic chalk grassland. Sheltered from the wind at this low level it was hot and still. We had not seen a Duke of Burgundy the other really rare butterfly to be found at Battlesbury Hill but this looked a likely spot. A small brown butterfly flew up but it was too small, diminutive as it whizzed around before coming to rest and on opening its wings revealed them to be chocolate brown with orange spots and white piping to the edges-another Brown Argus.

Dingy Skipper

Green Hairstreak

Dingy Skippers, and never was a butterfly so appropriately named, also flew up from the track and also another Green Hairstreak but little else until Peter exclaimed, 'There's one!' He had seen a small dark brown butterfly fly around but lost sight of where it went but he was convinced it was a Duke of Burgundy.We scoured the grass on the bank to our  left for some minutes and then Peter located it, a couple of feet from the ground, perched on the tip of a hawthorn twig, surveying the surrounding grassland awaiting any passing female.There might have been two but probably was only the one moving around in a small but restricted area. Latterly it seemed to prefer the grass to the hawthorn leaves. Nonetheless it was a great find and now we had seen virtually everything apart from a Grizzled Skipper, which we never managed to find.

Duke of Burgundy

Now we were at the bottom of an immensely steep slope, part of the fort's supposedly impregnable ramparts and looking up my heart quailed at the steep climb to get back up to the track running along the top. We tackled the climb slowly.There was no other way and our progress was lightened by the appearance of another Marsh Fritillary. Slowly we ascended and I reflected that if I was an invader back in those prehistoric days I surely would not have relished this route as the inhabitants hurled rocks and whatever they could lay their hands on from above and down on my head.

We got to the top and sat in the shade of some trees, feeling the coolness of the long green grass.We then walked south again, along the track we had walked at noon and followed it until we turned left to cross over the highest point of the fort, descending the other side and then back through the gate and down the bridleway to the car. I looked at my phone app and it told me we had walked no less than seven miles since our arrival.No wonder we felt tired. Back at the car we sat and rested before heading back to Oxford and relishing the satisfaction of having completed another rewarding day with some very rare butterflies.