Sunday 31 May 2020

A Bonanza of Glanville Fritillaries 29th May 2020

In May 2015 Peter and myself went to a nature reserve called Hutchinson's Bank, a steep sloping bank of chalk downland located near New Addington in the London Borough of Croydon. Our aim was to see a very rare butterfly called the Glanville Fritillary, named after its finder Eleanor Glanville.

They are only found here and on the Isle of Wight, so obviously Croydon was the easier option for us and setting off from Oxford in sunshine we were in good spirits but cloud moved in on the way and we were very fortunate to succeed in finding one Glanville Fritillary, for the brief period of time it showed itself in the cold, grey and unwelcoming conditions. As a butterflying experience it left us feeling somewhat unfulfilled.

I always resolved to go back to Hutchinson's Bank when the weather was more propitious and today, as with all the other days lately, was to be one of full sunshine and heat. A drive on pleasantly uncrowded roads due to the corona virus pandemic found me parking in Farleigh Dean Crescent and walking in on a bridleway to reach the reserve.

Hutchinson's Bank is 21.8 hectares in extent and is owned by Croydon Council but has been managed by London Wildlife Trust since 1987. It has recorded 36 species of butterfly and apart from the Glanville Fritillary, it is home to a large population of the Small Blue, yet another endangered butterfly.

I set off along the bridleway at around ten in the morning, the sun even now very warm and the chalk on the bridleway baked hard from days of sun. So bright was the sun, the light was almost white, shimmering and casting great shadows from trees and bushes as it reflected from the chalk, the grass scorched brown by days of heat.

The Bridleway with the reserve on the right.I found four Glanvilles sunning themselves along this bridleway
I turned off the bridleway and passed through a gate into the reserve proper and almost immediately found a Dingy Skipper, flying no more than an inch from the ground, before settling to absorb the sun's warmth. Was ever a butterfly better named? An insect with wings that were an unremarkable shade of greyish brown, with a few paler markings on its forewings, it wins nothing in a glamour contest but in its own unassuming way it posseses an attraction, albeit only apparent to a butterfly enthusiast.

Dingy Skipper
I was unsure where the best place was to go and look for Glanvilles and even uncertain if they were out yet, but I found a warden who told me they were indeed flying and I needed to go back down the slope to 'the cutting' which was the best place to look for the fritillaries. He told me he had seen several flying around there earlier in the morning.

'The Cutting.' A Glanville Fritillary hotspot
I followed the directions and on turning into the cutting immediately recalled this was where Peter and I had stood five years ago waiting to see a Glanville. The chalk bank on one side of the cutting looked ideal for fritillaries, with a mass of Ribwort Plantain and Kidney Vetch growing there but of fritillaries there was no sign. However there were many Small Blues flitting about the Kidney Vetch, the foodplant of their larvae and on which they lay their eggs. 

This tiny butterfly, hardly as big as the nail on my little finger, was here in profusion, flying about and then settling to open their wings to the sun, rubbing them together, in a slow deliberate motion  as if savouring the warmth. They too are unspectacular, like the Dingy Skipper, the male with just a suffusion of violet blue on its steel grey upperwing surfaces where they join its body, the wings outlined with the thinnest of white margins. The female is dark brown with no trace of blue at all but when they close their wings both sexes show undersides that are the palest silvery blue with a row of dots across both wings like a string of black pearls.

I wandered the few hundred metres of the cutting and then walked back and as I did so a fast flying butterfly skimmed across the grass, worn in places down to bare chalk by the passing of numerous feet and then flew back past me at similar speed to settle on a patch of bare  chalk, and there was my first Glanville Fritillary, with wings spread wide to allow its furry body to absorb the heat that would provide the energy to power it through the coming day. 

This was a male, newly emerged judging by its pristine appearance, showing a pleasing base colour of rich brownish orange on its wings, overlaid with a patterning of symmetrical, wavy dark lines, the wings edged with white. Sheer perfection. It moved frequently but always maintained a presence within a restricted area of a few metres, often returning to the spot it had just left. Eventually it flew off and did not return.

I do not know quite why I am always taken  aback at how small all the springtime fritillary species are but it always comes as a bit of a surprise. Every year is the same. Maybe it's because I am so used to seeing the much bigger, bright orange Silver washed Fritillaries of high summer in my local woods in Oxfordshire but despite my mistaken perceptions the smaller fritillaries are always wonderfully enticing and attractive to look at.

I waited to see what would happen and another Glanville appeared and like its predecessor flew fast and low above the ground before landing on some dogwood but unlike the other, nectared frantically with wings outstretched. Slowly it began to close them and here was my opportunity to get an image of the  underwing which in all small fritillaries is a marvel of complex patterning, and in the case of the Glanville a mosaic of wavy orange and white bands profusely dotted with black on the lower underwing while the upper underwing is mainly pale orange with just a white triangle at its tip.

A male Glanville on a Dogwood flower
This too moved off and I sat and pondered on what to do next but eventually decided to remain where I was as it was far from unpleasant in this so called cutting that was now functioning as an effective suntrap.

In a little while, with no further sign of a Glanville, I decided to move on and asked the warden, who was working nearby, if there were any other good areas to look for Glanvilles. He suggested a couple and I headed off to investigate but having only taken a few steps encountered another Glanville flying to feed on the white flowers of dogwood growing at the top of the bank. That was three Glanvilles so far, just in this one particular location

I took some more photos, not that I needed any more. A man came by and asked me what I was photographing and I told him  and he moved on without saying another word. Strange I thought but I was to learn later, chatting to him, that this was Martin and he was well known here, eccentric, maybe even a bit of a celebrity and he came here every day. A true butterfly addict and widely knowledgeable on the butterflies of Hutchinson's Bank and indeed of butterflies in general. I learnt a lot from talking to him and he told me he normally voluntarily leads guided walks and does transects on the reserve and has even raised Glanville caterpillars in his home for release at the reserve. 

Following the warden's suggestions I found four more Glanvilles all sitting on the bridleway in the full sun and reluctant to move very far from where I had disturbed them, returning in a low fluttering flight to settle once more on the hot dusty track. I met Martin again, coming the other way and we compared notes on how many Glanvilles we had seen. My total was now up to seven as was Martin's.

I returned to the cutting to sit on a bench with Martin and we talked butterflies, comparing experiences from our respective parts of the country. Martin told me about the breeding programme at Hutchinson's Bank and of the respective fortunes of the Glanvilles here and on the Isle of Wight, their true stronghold. He recounted how he and others were trying to widen and strengthen the gene pool of Glanville Fritillaries to avoid inbreeding and subsequent extinction. He told me that the female Glanvilles would appear in the afternoon and showed me a tiny cage on the bank to protect the eggs of a Glanville which had been laid on the underside of a Ribwort Plantain leaf. 

Eggs of a Glanville Fritillary on Ribwort Plantain and on which the caterpillars will feed.
Martin told me they are due to emerge in a couple of days
He told me the females sometimes look paler, are larger, their fatter body does not extend as far as the bottom edge of the lower wings, unlike the male, and their wings are more rounded. I resolved to try and get a photo of a female as, so far, I had only seen males.The time passed easily and comfortably in the company of Martin as we talked and then he told me about a large almost bare area called  'the scrape' that contained a huge number of Small Blues. I enquired where it was and he said 'come with me' and we walked along the bridleway, then through a tiny wood and out into the sun and there, through a gate was a large area of sparsely vegetated chalk downland. 

The Scrape harbouring hundreds of Small Blues
It was, as he said, alive with Small Blues. They were everywhere and just by standing I was surrounded by their tiny forms, moving like specks amongst the short grass, settling on blades of grass and Kidney Vetch. They were hardly still for more than a few seconds, scrambling over flower heads, chasing after rivals or females or moving their bodies on the blades of grass to align them with the sun but then, discontented would move on, forever restless.Martin told me he had counted 1500 on a transect here last year. 

Yet another Glanville was sunning itself here and a male Brimstone was trying very hard to mate with an unreceptive female. I walked around the perimeter of this large square and found a Marbled White and Meadow Brown, both my first for this year. It was butterfly bliss and I made the most of it. Martin left to go for lunch but said he would be back later. He repeated that the afternoon was a good time to see the female Glanvilles which would come to lay their eggs on the Ribwort Plantain in the cutting.

A Glanville Fritillary perched on Salad Burnet
I in turn walked back to the cutting, feeling warm and content and now found there were other enthusiasts here but only  four or five. I sat on the bench and watched them finding their own Glanvilles but was happy to remain where I was content in the knowledge I had all the images I required. As I sat on the bench other Glanvilles arrived and departed, some settling in front of me on the warm chalk. A Red Admiral, a Small Tortoiseshell and a Holly Blue added to the day's tally of butterfly species but really, today, it was all about the Glanvilles.

Male Glanville Fritillary sunning itself on Ribwort Plantain
The other enthusiasts departed and it was just myself and one other that remained. I took another turn along the cutting, checking the sunny bank and another Glanville arrived but something was different about it, as it did not fly like the others but was fluttering amongst the grass searching but never seemingly satisfied. Eventually it settled and I took some images of it before it began fluttering once more, moving up the bank and out of view and out of reach. Could it be a female? I suspected it was and examined the images on my camera and its body did indeed not reach the edges of the hindwings and it was fatter in the body too. I was still unsure as it was not that much paler but certainly it was  larger than the males I had seen.

Female Glanville Fritillary on its foodplant Ribwort Plantain
Later, on Martin's return I showed him the images on my camera and he confirmed it was a female and cleared up the question of paleness by telling me newly emerged females are often nearly as bright as the males.

I decided to stay on a little while longer but did not see another female Glanville, only a few males  but I did find another couple of Dingy Skippers and a really smart looking Grizzled Skipper.

Grizzled Skipper
At 3.30 in the afternoon I called it a day having seen at least twenty Glanville Fritillaries although one would have been enough.

Who could possibly ask for more?

Butterflies seen

Glanville Fritillary
Small Blue
Common Blue
Holly Blue
Large Skipper
Dingy Skipper
Grizzled Skipper
Small Tortoiseshell
Red Admiral
Marbled White
Meadow Brown
Speckled Wood
Small Heath
Orange Tip

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