Saturday, 27 February 2016

Everpresent on evergreen - a rare moth in Newhaven?

Ectoedemia heringella: is this tiny moth ubiquitous wherever Holm Oaks are located within the Lewes and Seahaven areas?

When I discovered some leaf-mines on a Holm Oak in Newhaven last summer, I was pleased to have found evidence of a nationally scarce species. Further fieldwork has led me to re-evaluate my initial excitement.

Ectoedemia heringella is one of one hundred species in the Nepticulidae moth family found in the UK. Each species in the family is tiny and heringella measures only 3mm in length (wingspan 4.5-6mm). Many of the adult Nepticulidae moths are similar in appearance, making it too difficult to separate most species on appearance alone. Their small size means they are rarely seen in their adult forms, but it is easier to find evidence of their presence during their early life-stage as a larva. This is because they feed within leaves, eating the tissue between the upper and lower surfaces of the leaf. As they progress through the leaf they leave a frass-filled trail behind them. Like a meandering river which can be followed from source to sea, the mine begins small, often near the egg, which may be laid on the upper or lower surface of the leaf depending upon the species, and broadens as the larva grows. The trail is called a leaf-mine. Many moth species and other insects have adopted this successful strategy during their early stages, including some fly species (Diptera), some wasps (Hymenoptera) and some beetles (Coleoptera). The genus Ectoedemia can be roughly translated as meaning 'outside swelling' (ektos and oedema) and this presumably refers to the appearance of the mines they create.

Ectoedemia heringella mines on a host plant at Riverside in Newhaven

Ectoedemia heringella feeds on Holm (Evergreen) Oak (Quercus ilex). The moth was first discovered in the UK in 1996 in Middlesex, but the record was not confirmed until 2001 (see UK Moths website). The species is native to the Mediterranean region from southern France to Cypress, where it feeds on Quercus ilex and Q. alnifolia (see British Leafminers website). It is possible that the accidental introduction to the UK was made during the importation of the host plant in the early 1990s. The mine created by the larva is strongly contorted and distinctive. An infested tree often has several individual mines on one leaf. One could speculate about how many adult moths may emerge from a single tree and reasonably suggest a number in the tens of thousands, perhaps more.

Ectoedemia heringella mines - many on each leaf

When I look at an infested tree it is reminiscent of the Horse Chestnut (Aesculus hippocastanum) and the notorious Horse Chestnut Leaf-miner (Cameraria ohridella). That species has infamously spread across Europe since its discovery in 1985 in Macedonia and has regularly attracted media attention in this country, probably because of concerns about its charismatic host-tree as much as anything else. Everyone loves the conker tree - including ohridella! Ectoedemia heringella has remained well beneath the radar compared with it, presumably because the holm oak is not as rooted in our collective hearts as the chestnut.

E. heringella has made the news, such as in a University of Reading Whiteknights Campus blog post and, hysterically so, in this Mail Online effort. It should be argued, however, that the photosynthesising potential of an infested tree would not be significantly compromised; only the mined parts of each leaf are affected in this way and the leaf is still able to properly function where chlorophyll remains. It is a reasonable suggestion that a heavily-mined leaf may be shed by the tree, but unless a critical threshold is exceeded, the health of the tree should not be too badly affected. This view may be somewhat subjective, however, depending upon where your interests lie: vegetable or animal.

The mines appear on the tough oak leaves in November, at a time of year when the deciduous tree species are shedding their leaves. This allows the recorder to pick out holm oak trees, which are as conspicuous in the wider landscape at that time of year as the mines themselves are on individual leaves in the macro-landscape. Larvae feed through the winter months and pupate in a cocoon between the leaves from April and appear as adults in June and July. It is an easy species of moth to find.

The species is given a provisional status of Nationally Scarce B (Davis, 2012), which suggests that, at the time, it had been recorded in only 31 to 100 hectads (10km x 10km squares) in the UK. According to the NBN Gateway, heringella is found to the south of a line drawn from The Wash to the Bristol Channel and from Hampshire eastwards.

Colin Pratt FRES, in his Complete History of the Butterflies and Moths of Sussex, Volumes One (2011) and Four (2015), provides a fascinating account of the history of the species within Sussex. It was first recorded in 2009 and only about sixteen records had been reported by early 2015 (when Volume Four was published), all following intentional searches for the leaf-mines. The sequential pattern of incoming records does not suggest a specific origin and colonisation of Sussex from elsewhere and this has led Colin Pratt to suggest that the moth might be a genuine overseas immigrant as well as an accidental import on holm oak saplings. The closest locations in which it had been recorded to the Ouse valley and Seahaven areas were Saltdean, Telscombe and in the Ouse valley itself at Piddinghoe, so it was probably already present in the Newhaven area by 2014 when these records were made.

I first discovered the moth on 29th July 2015 at Meeching Down SNCI, locally known as The Union Field, which is located to the west of Newhaven. This was during a children's bug-hunt in which I was assisting the SCDA and Lewes District Council. I noticed the distinctive mines on a low bough of a single oak close to the A259 Brighton Road. When I revisited on my own I counted well in excess of 300 mines and there were probably significantly more beyond my reach. Such an infestation on a single tree suggested that it might be found on other holm oaks in the area and I added a leaf-mine search to my winter to-do list. I finally managed to do some more work this February.

I was aware of a handful of  holm oaks in Newhaven so, on 14th February, I started inspecting them. Starting at Castle Hill LNR, I inspected trees in Riverside, just a few metres from the congested one-way system, and in Church Hill. Widening my search I inspected a plantation of seven holm oaks growing around the boundary of the Church of the Ascension at the junction of Arundel Road with Steyning Avenue in Peacehaven. A further four holm oaks were inspected in the Southover High Street area of Lewes. Trees at every location that I inspected were host to heringella - and often in very high numbers.

As winter began giving way to spring I continued to search for host trees and found them in numbers in Lewes (Brighton Road, Broomans Lane, The Pells area, Lewes House), Swanborough, where a truly mightly oak was affected, Rodmell, the churchyard of St. Mary's at Tarring Neville and Poverty Bottom near Newhaven, where only a few mines were seen amongst a heavy infestation by another Quercus ilex-feeding moth, Phyllonorycter messaniella. Perversely, messaniella is considered to be a common moth (which it is), but this is the only location at which I have seen it on Holm Oak.

So to conclude, while Ectoedemia heringella may still warrant its nationally scarce status, it does appear to be locally abundant - if the numbers seen in the Lewes and Seahaven areas are anything to go by. There are several further Holm Oaks that I have spotted during my travels and made a note of to check at a later date. I suspect that the known distribution of this moth will grow with almost every tree that is inspected.

The Holm Oak at Church Hill in Newhaven - about 40 years old
Some of the seven Holm Oaks at the Church of the Ascension, Arundel Road, Peacehaven
The Holm Oak between St. John The Baptist Church and Priory Crescent at Southover High Street, Lewes
The magnificent mature Holm Oak near the Cockshut Road junction with Southover High Street in Lewes

The Drove, Newhaven
Avis Road, Newhaven
St. Mary's Church, Tarring Neville

Swanborough Drove
Swanborough Hollow/Lewes Road

Southover Grange Gardens

The Pells, Lewes

Castle Banks, Lewes

Sunday, 21 February 2016

Cutting brambles at Barrow Head

Restoring a mixed grassland habitat for the Common Blue butterfly (Polyommatus icarus) on the slumps at Castle Hill LNR in Newhaven

In February, the sun-splashed, salt-stunted grassy slumps beneath the cliffs at Barrow Head are largely absent of human activity. The occupation by hordes of barbecue-brandishing sun worshippers and their competing beat boxes are still five and a half months away; for now only the occasional dog walker ventures off the ribbon of vegetative shingle onto the slumps. The rabbits and voles need concern themselves only with the fox and the kestrel amongst their daily anxieties.

The Barrow Head rabbits are a depleted race; once numerous enough, perhaps, for the headland name to have been re-Christened in their name as their burrows became the noticeable feature following the geological demise of the barrowland. The rabbits have melted away themselves over the decades and their nibbled turf has become neglected so that the few remaining burrowers cannot compete with the advance of successional vegetation: the slithering bramble and brittle-boned elder which have slowly and ominously emerged the victors in a turf war across the slumps. The salt-laden Channel winds do their best to slow the advance, but these are winds which lack the fury of an Atlantic or North Sea gale. Channel winds are soft in a way which the Welsh writer Edward Thomas understood in his 1909 book The South Country

...the South is tender and will harbour anyone; her quiet people resent intrusion quietly, so that many do not notice the resentment. These are the "home" counties. A man can hide away in them. The people are not hospitable, but the land is.

Common Blue (Polyommatus icarus)
The slumps are a habitat in flow, particularly so in February. The chalk cliffs of Barrow Head are topped with layers of change: London and Woolwich clays, sands, raised beach, lignite and a rendzina crowned with short-cropped fescue and thrift. These flow, perhaps in emulation of the Ouse river a stone's throw to the east, from the clifftop downwards in a glacial dance onto and into the slumps, plump with the weight of the winter's rain. Castle Hill's barrows, after which the small headland is named, have long since melted away into the slumps below, noticed or not by the eyes of man. But the flow is not always glacial in character, a smooth progression of melting clay or fossilised oyster bed dancing across deep time; it is seasonal, sudden and catastrophic and some February inspections reveal the gashes and scars of a sudden night time slip or collapse of sandstone.

Wild thyme and trefoil
The sandy, ligneous soil forming the slumps is well drained and offers a suitable habitat for Sedum: biting and white stone-crops which flower sulphur and white in the summer. This two-tone tableau carpets the exposed soils, filling the gashes and scars of winters past. Amongst these one can find burrowing invertebrates such as solitary bees and wasps, beetles and hunting spiders. Their exposed habitat relies on change. If the flow from above was to cease, the barren ribbon of soils would engage in a succession of the grasses and sedges which can be found a little lower down the slumps and, as their roots take hold of the soils, rhizomes of bramble would sneak in and begin to suffocate the lower plants and their denizens. The burrowing insects would be replaced by cone-heads and Roesel's bush-crickets, which already chirrup and drone further down the hill, but the loss of the marginal habitat and its tenants would be very difficult or impossible to replace once it is gone and the character of the place would become more uniform, less diverse.

It is a mistake to look upon the Barrow Head slump and see only a wasteland of slipped ground, useful only as a site for disposable barbecues, a resting place of windblown litter or to utilise as an outdoor latrine. There are contours of life here: narrow bands of neighbouring communities which exploit ribbon-like bio-halines. These specialist niche-dwellers of the slumps collectively amount to the richest biological community anywhere within the Castle Hill Local Nature Reserve. The resident stonechat pair seem to know this. These ribbons require a well-considered eye and hand to ensure they are performing well. The suffocating tangle of bramble must be held in check and this is the reason why our work-party is visiting today.

We arrive with our tools, down them and stand in a cluster to ponder the landscape. The slumps' grassland areas have been choked by encroaching bramble during recent years and it came to our notice the previous year when numbers of butterflies experienced a significant decline. The grassy undulations, now smoothed by crowns of bramble, were in previous years host to a colony of common blue butterflies, which laid their eggs on bird's-foot trefoil. Mixed clovers fed the Mother Shipton and Burnet Companion day-flying moths; countless noctuid moth species nibbled away at grass roots and, as adults, they shared the shelter of the grass tussocks with foreign visitors such as Silver Y and Rush Veneer. The loss of grass and flowers means also the loss of the invertebrates which rely upon them. The birds which are fed by their lower trophic levels shelter in the bramble perhaps less certain of their next meal.

Our group of friends have pondered how to tackle the thicket. We debate the need for sheep - their grazing power would do the trick! To fence the sheep in would be a simple and satisfying task, but fencing out humans and their dogs is considered by all to be an impossible goal. Everything growing before us has endured despite the behaviour and activity of many people and their pets and any livestock, however lookered, would be placed in a precarious situation, however optimistic or diligent we may be.

Sedum, sulphur and white growing above the Barrow Head slump
We agree to leave in place a protective skirt of bramble a few metres thick along the cliff bottom and to remove anything below it. There are some considerations and negotiations to be made: what will happen to the cherished colonies of Roesel's bush-cricket and long-winged cone-head, which we recorded around the thicket the previous summer? We agree that the next generation of these species will emerge from their protective grasses as nymphs and, if desired, shall migrate slightly uphill to the remnant bramble. Where shall we have a fire? Must we scorch and lose another patch of grassland? After much debate and concern about the practicalities of carrying a prickly cumbersome mass of bramble down to a remote fire site and the prospect of sacrificing a remaining patch of grass to a fire, we agree to cut a patch of bramble and build the fire on the exposed ground. How should we actually cut the bramble? It appears to be more involved than lopping and sawing through the scrub of gorse, blackthorn, hawthorn and sycamore on the northern slope of the reserve. We decide to learn through doing and get to work.

We agree to leave in place a protective skirt of bramble

Tired arms
Burning the tangled, rolled fleeces is a pleasurable affair
It quickly becomes apparent that cutting bramble is hard work. One has to adopt a crouching posture, so as to work at the level of the lower stems, but also to ensure a reasonable working distance from the thorns. Legs and arms are not as protected as hands and, soon after cutting commences, as body temperature rises and layers are cast off, they are protected less still. A few explorative snips with a lopper persuade me that progress can only be made with a less discriminatory set of shears: several cable-thick stems may be cut at once instead of a single stem at a time. I swap tools and progress through the stems. We learn that the best method for removal is to imagine we are shearing a sheep and begin working with a partner, cutting and rolling, cutting and rolling, one shearing through the spinous fleece, bristling with thorns, the other rolling the cut fleece over, pulling it back to enable the next cut.

The hard work takes its toll and my forearms tire too quickly. The slashes of my shears slow, soften and cease. The lactic acid burn would penetrate so deeply into seldom-used muscles that I would not enjoy full use of my aching arms for six full days. When I stop and sit by a cleared patch I notice for the first time just how much new habitat we have created. If the potential for blue butterflies could be measured in satisfaction, we had enjoyed a very satisfying morning of hard work. The resident stonechats, perched almost within an aching arm's reach behind me, clack in appreciation.

Burning the tangled, rolled fleeces is a pleasurable affair. The flames take hold of the brambles with enthusiasm. I stand a distance from the heat and imagine that the potential for harm held within each thorn can be measured as a unit of energy. As the flames sweep through the newly added bundles, the crackles and pulses of flame mark the demise of one thorn after another. No longer shall they catch hold of my boot or pierce my skin; no longer shall their stems and leaves shade the trefoils and their butterflies from the sun.

...we had enjoyed a very satisfying morning of hard work.
Barrow Head and restored slump
Cleared bramble, exposed land
Cleared bramble and fire site

Wednesday, 10 February 2016

Back into the Motherlode

A rich seam of hibernating moths and butterflies runs beneath the wintry land at Newhaven Fort and its stunning and embracing neighbour, Castle Hill Local Nature Reserve. They stand together, arm in arm, overlooking the Ouse estaury and facing the full force of the bracing English Channel winter. The historic tunnels are dark, damp, ventilated, mild and these conditions are stable. The temperature within the tunnels is consistently between 1°C and 2°C warmer than the ambient outside temperature. Any adult insect seeking an hibernaculum would increase their chances of surviving the winter as they fly into the tunnel entrances or ventilation shafts here. Buried alive each autumn to be reborn the following spring. We ventured into the dark, damp shafts twice during the 2015/2016 winter. This was the second winter of what we hope will be regular annual surveys. This is an account of what we found.

Outside and in: inside the southern counterscarp gallery
Outside and in: outside - the area close to the southern counterscarp gallery

Our first survey during this winter was made on 15th December 2015. The outside world was halfway through experiencing the warmest December on record and I was interested to learn whether the mild conditions had affected the number of hibernating insects within the tunnels. It had not; we saw very nearly the same number of insects as we had during the previous December. So does day length rather than temperature drive adults into hibernation, or is there a complicated juxtaposition between the two? All good tunnel surveys should generate more questions than you begin with - it's part of the journey.

Two new species were added to our list: Acrolepia autumnitella (Bittersweet Smudge) and Amblyptilia acanthadactyla (Beautiful Plume). Acrolepia autumnitella feeds as a caterpillar on bittersweet or deadly nightshade. The tiny caterpillar feeds within the leaves and creates characteristic pale blotches. As an adult, it remains small at about 6mm long, but its inconspicuous appearence is betrayed under magnification, revealing a macroscopic beauty in its brindled patches and pale cross-lines. There are two broods in most years, in July and again in October, when the adults hibernate and emerge the following spring to produce the next summer brood - exactly what our individual was doing. Photographs and further information about this and all the species described below can be found by following the links.

The Beautiful Plume (Amblyptilia acanthadactyla) is a common but spectacular little moth, which appears to have become more common during recent decades. It feeds in its early stage on a range of herbaceous plants and, similar to autumnitella, the adult flies in July and again in September, when it seeks hibernation.

Although total numbers were similar to those in 2014, there was an interesting variation in the numbers of individual species. The Bloxworth Snout (Hypena obsitalis) was present in almost the same numbers (thirteen this year; fourteen in 2014), as were Small Tortoiseshells (Aglais urticae), with six counted both this year and last. The Twenty-plumed Moth (Alucita hexadactyla) was more numerous with 47 seen this year compared with 32 last December. This intriguing little moth somehow chooses a resting place which, despite the pitch dark, often provides a cryptic background, for example a pebble-dashed wall. This makes it a challenging species to count with a headlamp, but perhaps the greater number seen this year suggests we have got our eye in better than we had during our first visit last year.

The Peacock (Aglais io) was seen in fewer numbers this year than last
The greatest contrast in numbers was seen in the Peacock (Aglais io). In 2014 we counted 33 individuals; this year we saw only twelve - nearly two-thirds less. Perhaps this was because fewer adults had survived this year to the point of hibernation? Perhaps last year's number will prove to be unusually high? More questions requiring an answer! Jean Jacques Rousseau once wrote that patience is bitter, but its fruit is sweet. This I am learning. We saw a total on ten species and 112 individuals during this survey, which has proved to be our best result to date, but only just greater than the very similar result obtained in 2014 (eight species, 109 individuals).

Curled autumn leaf: The Herald (Scoliopteryx libatrix)
Our second and final visit of this winter was made on Tuesday 2nd February. Why do we survey twice each winter? I don't know whether there is any value in this just yet, and a good enough reason might emerge during the coming years. For now, a second survey enables an interesting comparison with the earlier winter survey - a before and after or early- and late-winter evaluation. One clear benefit of a second visit is that it fulfils a need which grows within me during a long period which is otherwise absent of moths and butterflies. So the flame of personal gratification is perhaps the strongest attractant. But there is also a fascination that many of the individuals discovered during December have not move a single millimetre during the five or so weeks between our visits. There is a pattern emerging to this: certain species appear to enter a deeper slumber than others. For example, the butterflies - those poster boys of hot summer days - are regularly found in the same state in February as they were in December. The same may be said of the stunning Herald (Scoliopteryx libatrix), which hangs like a curled autumn leaf from the tunnel walls. Also apparently less active is the tiny micro-moth Digitivalva pulicariae (Fleabane Smudge), which inexplicably appears to seek the same section of deep tunnel a long way from the outside world and in which no other moth or butterfly species has so far been found.

A reluctant slumber? The Bloxworth Snout (Hypena obsitalis)
More active is the Twenty-plumed Moth, which will often flutter back into activity under torchlight. But by far the most restless species is the one we are the most interested in: the Bloxworth Snout. During the four surveys we have performed, the Bloxworths have proven to be sensitive to light, taking to flight as torchlight falls upon them and flying a short distance before settling down again. In February 2015 we counted only five of the fourteen individuals we had seen during our first visit in December. It seemed a fair suggestion that they were more tolerant than other species of cooler temperatures - a behaviour which is often witnessed in the outside world during the early and late winter, when they are seen around doorways - and that the Bloxworths emerge from a comparatively lighter slumber ahead of some other overwintering species. Does this convey some ecological or evolutionary advantage? Would this winter's second survey suggest the same behaviour? As well as one stand-alone survey could suggest this, yes it did: only seven of the thirteen individuals counted in December remained and the others were not seen. Of the ten species seen on 2nd February, only the similarly active Twenty-plumed Moth was seen in noticeably fewer numbers: 28 individuals compared with 47 seen in December. The numbers of both these species had roughly halved. Only patterns which emerge in future tunnel surveys will provide more robust data to these initial findings, but it is one of the more interesting findings we have made to date. Until December, patience.

One of the Bloxworth Snouts seen in February 2016
Another of the Bloxworth Snouts seen in February 2016

The Herald (Scoliopteryx libatrix) - a spectacular moth which is associated with Poplar and Willow