11th June - Blean Woods, Kent

 A trip to Kent to visit my daughter and granddaughter provided a window of opportunity to try and find my second new butterfly of the year.  The weather was perfect, sunshine and clouds with a breeze and after some internet research I was off to the Blean Woods complex just outside Canterbury in Kent.

The Blean Woods are a collection of four woods and these comprise of 10 square miles of ancient woodland.  The woods are semi-natural woodland situated on poorly drained London clay, with a small area of gravelly soil in the south. The underlying clay results in much surface water and mud in winter and wet summers.  The wood has been heavily managed in the past as wood pasture and as a source for sweet chestnut coppice, in the past it was traditionally a source of wood for charcoal.

I parked just off the A290 and then took a path that led west into the woods.  The path would go through thick cover and then open out into various open glades and rides where the undergrowth had been cut well back and cleared leaving small shoots of bramble and giving the flowers opportunity to thrive.

From my research Cook's Glade was the place to be and I soon realised from the map that I had wandered well away from that area, so I turned around and retraced my steps.  It was now just after 10:00 am and I hadn't seen a single butterfly on my walk, which was a little concerning.  However as i walked past one of the cleared spots I noticed an orange butterfly drift over the ground.  I crossed the ditch by the side of the track and followed the butterfly as it looked for somewhere to settle, eventually it did and I had my first ever Heath Fritillary

It was a little disappointing that my first Heath Fritillary was a little damaged and not a pristine perfect butterfly, but it wasn't to be the last and pretty soon I was finding others around the cleared area.  In fact I came across this mating pair, one of which appears to be the first one I had found, the little nick in the wing giving it away.

The upper-side of the butterfly is predominantly dark brown and orange-brown, with the orange-brown spots delineated by dark brown (along and across the wing veins); there is a white fringe to the wings through which the dark brown extends. The upper-side of the body is a similar dark brown to the colour on the wing, and the base of both wings is dark brown. The underside shows bands of red and (off-)white, again with each vein dark brown and each colour delineated by dark brown. 

Alongside the mating pair was a single butterfly taking in the morning sunshine

But it was aware of the couple and tried to muscle it's way in.

The attempt to unseat the rival male failed and the single butterfly returned to it leaf while the couple continued.

The butterflies were not that dynamic, continuing their session on the wood sage leaf and after a while I began to notice the bird calls from within the scrub surrounding the clearing.  It was a whistle and a sound that is probably best described as a creaking 'errr'.  At first it didn't register, but then I realised that it was a Nightingale and that there were two of them in the scrub.  Positioning myself at a spot where there was an opening in the scrub I was able to see them moving about, but they never stayed in one spot long enough for a photograph.

In all there were eight different fritillaries in the clearing, but I was still looking to find Cook's Glade so I left the clearing and joined the main track to retrace my steps. On the way in I had passed an RSPB information board and from the map it looked like this could be close to the place I was searching for.  Turning right there was an open area with bracken and grasses and more Heath Fritillaries.

There was even another butterfly, the Meadow Brown.

Positioned at the side of the glade there was a bench that had a good view across the glade, when the sun went behind the clouds the action eased, but once it came back out there were Heath Fritillaries everywhere.

The Heath Fritillary is only found in four landscapes in the United Kingdom: The Blean Woods complex here in Kent; woodlands in southern Essex; the heathland combes of Exmoor in Somerset and the Tamar and Lydford valleys of Cornwall and Devon.

The butterfly was considered on the verge of extinction in the 1980s and this may have become a reality were it not for concerted conservation work in the ensuing years. However, despite these great efforts, the status of the Heath Fritillary has continued to fall and remains of great concern.

Traditional management practices such as coppicing and ride management are required in woodlands and on moorland sites extensive grazing along with burning to tackle the gorse and scrub encroachment are necessary, to create ideal conditions for egg laying and larval survival. 

Although very local in its distribution, this butterfly can be seen in large numbers at some sites in good years.   This butterfly forms discrete colonies and rarely strays from the main breeding grounds.

It was very difficult to be exact because there were so many butterflies, but I would estimate there were well in excess of fifty here in Cook's Glade.

Where the conditions are open, after the coppice is cut, much of the ground is colonised by common cow-wheat, which is the food plant of the caterpillar of the Heath Fritillary butterfly. As the chestnut grows up again and the shade becomes denser, the habitat becomes unsuitable for the flowers and butterflies, therefore it is very important that regular coppicing is carried out to maintain open areas for our colony of one of Britain's rarest butterflies. The older coppice is, however, valuable for nesting birds such as warblers and Nightingales so a regime of careful rotation of coppicing is required.

The ecology of the Heath Fritillary has been extensively researched since the 1980s and it is known to be reliant on early successional habitats. Targeted management is required to provide the ideal conditions for the species where the principal larval host plants of Common Cow-wheat and Ribwort Plantain are plentiful.

Common cow-wheat is an annual of woodland edges, heaths and upland moors that has deep golden flowers from May to September. It is a hemi-parasitic plant, meaning that it relies on obtaining some of its nutrients from the roots of nearby plants. The nectar of Common Cow-wheat can only be reached by insects that have a long proboscis, especially bees. If the flower is not pollinated, it will pollinate itself.

The leaves of Common cow-wheat are narrow and pointed. It has yellow flowers that grow in pairs up the square stem, both facing the same direction; the first pair to emerge are those at the top of the stem.

Common cow-wheat has a mutually beneficial relationship with the Wood Ant of which there were many to be found as I walked around the woods. The flowers produce a sugary liquid from tiny glands below the petals that the ants are attracted to and feed on. The seeds of the plant are very similar in appearance to the cocoons of the ant and are transported back to the nest where they can grow.

Another different butterfly appeared for a brief while, the Holly Blue.

But it was very difficult to pull away from the many Heath Fritillaries.

Going back to the conservation work, in the Blean Woods the occupancy of the butterfly is dynamic and targeted management is required to provide a regular resource of suitable habitat patches (coppice coupes or sections of rides) for the butterfly to colonise and occupy while they remain suitable (usually <6 years for coppice). Targeting habitat management is key to maintaining occupancy and abundance. 

Researchers at the University of York used Heath Fritillary data to build a simulation model that would help to target the area and spatial location of management. The resulting model confirmed that the observed rates of coppicing were not enough to meet conservation targets, under a ‘worst case scenario’ model the populations could be sustained if the coppicing area increased to approximately 30 ha per year. Targeting of the management is vital as the four woodland blocks are interdependent, with movement occurring between woodland blocks. This research has helped us, working with the various landowners, to target our advice and management priorities. 

Here the long-term population trend is stable, although there have been declines over the last four years along with a reduction in the size of colonies. The cause of this decline is possibly related to a recent reduction in management levels within some parts of the woodland complex potentially as a result of the restrictions around the Covid pandemic. This has now been reversed and we would expect the species to respond positively again which will continue to be monitored. Anecdotal evidence is suggesting that climate change is impacting on the abundance and phenology of the host plant and this is an area for further research. 

I dragged myself away from Cook's Glade and followed one of the smaller paths that lead through the woods, I came across another Nightingale, but like the others it would not show well enough for a photograph.  I decided on walking a loop around the woods in the hope that I could find some more butterflies, but like when I arrived there was very little about other than Heath Fritillaries.  I did mange to see a Red Admiral, a male and female Brimstone and a Speckled Wood.

On the return loop I came across several more Heath Fritillaries and the count by now had to be well in excess of one hundred.

I followed the path back to the main track and returned to Cook's Glade where the Heath Fritillaries continued to fill the open spaces and could be seen flying between the bracken and chasing each other around.  I watched the spectacle as I ate my lunch and then my time was up and it was time to return.

I had finally managed to see my first Heath Fritillary which was then quickly followed by over a hundred more.  Quite a spectacle and the Blean Wood Complex will definitely be due another visit next year when there will be the opportunity to pin down the Nightingales as they sing and also maybe Pearl-bordered and Small Pearl-bordered Fritillary.