Giant Horsefly in Exeter

Last night I found a Dark Giant Horsefly (Tabanus sudeticus) on the wall of the Devon and Exeter Squash Club. This is the largest horsefly in Britain and they don’t get any bigger anywhere else in the world including the tropics.

The body is 24mm long – the orange base to the antennae and dark markings on the abdomen are diagnostic. This is a female – they have gaps between their eyes. In the males their eyes touch.

I’m not sure what it was doing at the Squash Club, I’ve normally seen this species in wild remote places like the Highlands, the Lake District and Dartmoor. I wonder whether it had been affected by yesterday’s heavy rain and took shelter before setting off again in search of cattle and horses.

Here is a photograph of the same species – one I took on Dartmoor a few years ago with a pound coin for scale

This is the same individual showing its mouthparts – it is only the females that bite – little reassurance though as this is a female!

This is the national distribution of the Dark Giant Horsefly – not very common

A Western Bee-fly in my garden in Exeter

Yesterday in the warm sunshine I came across a very small bee-fly in my garden. I have regularly seen the larger Dark-edged Bee-fly (Bombylius major) but I have never seen a Western Bee-fly (Bombylius canescens) in the garden before. If I want to see one of these I normally go to Hembury Woods on Dartmoor.

Distinctive bee-fly with its long proboscis – the animal was around 8mm long

Feeding on Germander Speedwell flowers – gives a good indication of the size of the bee-fly

The dark core with the lighter fringing hairs is distinctive.

As you can see from this distribution map (courtesy of the NBN) it is not a common animal

The problem with Heather Beetles

The Heather Beetle (Lochmaea suturalis) is a native Chrysomelid leaf beetle which feeds almost exclusively on heather (Calluna vulgaris). It is common in areas whether heather grows from the south of England to Orkney in the north (Duff 2016).

Heather beetle populations are well known to fluctuate greatly from low numbers which have little over impact on heather plants to very high numbers which can lead to the widespread defoliation of heather and can cause its death.


Heather Beetle damage on Ryders Hill March 2016

Heather beetle outbreaks have historically been problematic for grouse moor owners and the issue of heather beetle and its control has been championed by the Heather Trust who have produced a short document on the species (Heather Trust undated).

In addition the Heather Trust commissioned a literature review of the species (Rosenburgh & Marrs 2010) which summarises the ecology of the beetle, its impact as a pest and strategies for control. This work has been updated (Gillingham et al 2015a and 2015b) and published as Natural England Evidence Reviews on its ecology and its management.

These reviews state the following regarding heather beetle outbreaks:-

  • ‘Considerable damage to heather can occur with complete death in the worst cases’.
  • ‘Large scale vegetation change can follow’ (heather outcompeted by invasive grass species).
  • ‘The occurrence and severity of heather beetle attacks appears to be made worse by increased levels of nitrogen in the soil and plant tissues, which has been blamed on high nitrogen pollutant inputs from the atmosphere in recent years’.
  • ‘The high nitrogen in the leaves provides the beetles with more high quality food to consume’
  • ‘Climate change is expected to lead to increased winter survival of heather beetles’

On Exmoor heather beetle is considered a major problem, and the National Park Authority report that outbreaks are common and are spreading from the south to the north of Park. They also suggest that in areas where Purple Moor Grass (Molinia caerulea) is absent the heather plants recover fully and rapidly but where Molinia is present this quickly swamps the heather and replaces it (ENPA 2015).

I have written before about the loss of heather that had occurred on the National Trust’s land in the Upper Plym valley on Dartmoor (see here). In 1995 there was a serious outbreak of heather beetle which killed off the heather in the area known as Hen Tor Fields. At the time it was assumed that overgrazing was the cause although no increase in stocking levels had taken place for a number of years.  In this specific instance the heathland communities (H12 Calluna vulgaris-Vaccinium myrtillus) were replaced by upland grass communities (U4 Festuca ovina-Agrostis capillaris-Galium saxatile) which do not naturally contain Molinia. On the wet heaths of the Upper Plym Estate there were numerous other outbreaks on heather beetle during the 1990s and 2000s (Helen Radmore NT tenant pers comm) and in these habitats Molinia now dominates (my observations).

There has been no systematic survey of heather beetle on Dartmoor and Goodfellow et al (1997) only briefly mention it “Outbreaks of heather beetle cause local declines in heather”, however my recent observations on the moor suggest that heather beetle damage is very widespread and extensive.


Heather Beetle damage on Ryders Hill – March 2016

I would be very interested to hear from anyone with information about heather beetles on Dartmoor in recent years – it is an issue which is begging for more research.

References
Duff A.G. (2016) Beetles of Britain and Ireland. Volume 4 Cerambycidae to Curculionidae. A.G. Duff (Publishing) West Runton.
ENPA (2015) Exmoor Swaling Review 2014/15. Seminar Notes ENPA. Dulverton. http://www.exmoor-nationalpark.gov.uk/__data/assets/pdf_file/0011/583454/Exmoor-Swaling-Review-2014-15.pdf
Gillingham P., Diaz A., Stillman R. & Pinder A.C. (2015a) A desk review of the ecology of the heather beetle. Natural England Evidence Review, Number 008. http://publications.naturalengland.org.uk/publication/6386866406293504
Gillingham P., Diaz A., Stillman R. & Pinder A.C. (2015b) Desk review of burning and other management options for the control for heather beetle. Natural England Evidence Review, Number 009. http://publications.naturalengland.org.uk/publication/4817807814426624
Goodfellow S., Wolton R. & Baldock N. (1997) The Nature of Dartmoor: a biodiversity profile. English Nature / Dartmoor National Park Authority publication. http://www.dartmoor.gov.uk/__data/assets/pdf_file/0014/42701/au-natureodp2.pdf
Heather Trust (undated) Heather Beetle. Download from Heather Trust Website http://media.wix.com/ugd/fdc287_2b9ec8fa073d4ca38baf4a754d7a77f4.pdf
Rosenburgh A. & Marrs R. (2010) The Heather Beetle: a review. Report to the Heather Trust. http://media.wix.com/ugd/111722_4370d9fb976442b2af6e678aa83c3663.pdf

Some different sheep at the magical Challacombe

I was up at Challacombe Farm yesterday afternoon for a site visit to see and discuss the work of Naomi Oakley and Mark Owen who farm this Duchy Farm. It was a field visit which was part of a 2 day workshop entitled ‘Locally led agri-environment schemes – from a farmer’s perspective.’ I’ll report back on the workshop at a later date – in the meanwhile here are a few photos I took at Challacombe.


Naomi showing the extent of her farm and its large number of associated archaeological features.


Reporting back on the bracken management project


The slopes of the valley showing the Mediaeval lynchets – see here for more details on these.


From the barn up the valley to Hameldown Tor


In the barn Naomi shows of three different breeds of sheep which are being kept for their wool – the little dark one at the front is a Black Wensleydale – a very rare breed – see here. The white sheep at the back are Wensleydales – see here.


The sheep with the black and white faces are Zwartbles – famous for producing  an excellent fleece – really good to see wool coming back into profitability again (assuming you use the correct breeds) – see here for more details.


Here are a few Wensleydales out on an in-bye pasture.And this a hardy Welsh Black Mountain Sheep – small but very efficient at grazing around the Scheduled Ancient Monuments.

We also visited the amazing Rhos pastures at Challacombe –  wet valley mires – in the summer they are buzzing with life – I’ve written about these before – see here and here.

 

Finally …. can really recommend this book – tells the amazing story of sheep in Britain – from the times when wool created the country’s wealth right through to the dominance of sheep for lamb. The last chapter won’t be to everyone’s taste as Philip Walling is clearly very angry of the recent controversies regarding ‘overgrazing’ and the subsequent reduction in the national sheep flock. The book though does give a wonderful introduction to sheep breeds, where they came from and where they now survive.

A great afternoon at a magical place.

Managing Purple Moor Grass

According to Ian Mercer (in his Dartmoor New Naturalist book pp118-120) around 35% of Dartmoor’s Commons are now dominated by Purple Moor Grass (Molinia caerulea) – now often just referred to as Molinia. It is considered to be a major problem for the Commoners as it shades out the more nutritious grasses and a major problem for conservationists as it dominates habitats and reduces the dwarf shrub communities such as heather.

The reasons behind the increase in Molinia are contested and unclear. Overgrazing and over burning have been blamed as has the increase in sheep grazing as opposed to summer cattle grazing. The conservation agenda as articulated and prescribed by Natural England has been to promote increased spring grazing by cattle and reduced burning (swaling). Mercer telling says the following ‘the system that allows a hill-farmer to maintain a good enough herd of the hardy stock and of the right number all year round to be profitable and to follow current nature conservation thinking about a regime for blanket bog vegetation management has yet to be devised.’

This conundrum is at the heart of the debate on Dartmoor about favourable condition and the extent / decline of heather on the moor.

Last September the National Trust team based at Marsden Moor in Yorkshire organised a three day conference on this very topic (it is a major issue for all upland areas in the UK not just Dartmoor). I unfortunately was unable to attend the conference but fortunately the proceeding have now been published.

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You can download this 200+ page document here.

If you are interested in the quality of our habitats in the uplands then this document is essential reading. The report consists of a number of scientific presentations from the country’s leading experts along with a series of case studies describing the actions and outcomes of a number of site managers.

This is a major contribution to understanding the management of our uplands and it shows how complex the problem is.

For example, Rob Marr and his team from Liverpool University replay their research from the early 2000s which told us that grazing and burning regimes in isolation will not solve the problem, they only got reductions in Molinia when they also used herbicides.

Simon Caporn’s team explain the role played by atmospheric pollution and tell us that whilst sulphur dioxide pollution is now a thing of the past, nitrogen deposition is definitely on the increase and that this along with rising carbon dioxide levels (as a result of climate change) and ozone may very well be promoting the growth and spread of Molinia.

These presentations (and all the others) are well worth reading and mulling over as they explain why the quest for ‘favourable condition’ in the uplands is currently so elusive.