Conservation

This part of the site discusses the rarity, or otherwise, of our mistletoe Viscum album, with some notes on other European mistletoe species. It also discusses the wider conservation value of mistletoe, its importance in biodiversity, supporting other species. Quick links to these sections are below:

Where mistletoe grows

All mistletoe species

Viscum album is a widespread species, occurring over most of Europe and into Asia. In the context of all the mistletoe species worldwide it is one of the most widespread, with most of the other 1500 or so species more restricted.  This map (right) gives an indication of the area the others inhabit – throughout the tropics and the southern hemisphere but petering out in the far northern hemisphere.

Mistletoe Distribution in Britain

Mistletoe distribution in Britain (apologies to Scotland, but there’s hardly any to show there)
Mistletoe distribution in Britain (apologies to Scotland, but there’s hardly any to show there)

Studies of mistletoe distribution in Britain took place in the 1970s and the 1990s. Results of these are discussed lower down this page. A new national assessment project was launched in November 2023 to update the previous work and to gather new information on quantities of mistletoe. This is a new measure, previous studies recorded locations only, not amounts. Details of the new project, app-based and called  mistleGO!, are available on the Tree Council website here.

In Britain most mistletoe (we only have Viscum album here) is found in the south and west midlands, with particularly good populations in Herefordshire, Worcestershire, Gloucestershire, Gwent and Somerset.

There is mistletoe elsewhere, particularly in the south, plus a few rare occurrences in north and east England, Wales, Scotland and Ireland.

But it is only regionally abundant in that core area of the south-west midlands.  Many assume this to be somehow linked to apple orchards (apple is a favourite mistletoe host, and orchards a favourite habitat). This assumption is  incorrect – there are many apple orchard areas elsewhere in Britain that don’t have mistletoe, and studies across Europe link mistletoe distribution to particular climate preferences, which do seem to match the main distribution in Britain.

Enlargement showing mistletoe distribution in the south-west midlands
Enlargement showing mistletoe distribution in the south-west midlands

You can see some clear climatic preferences, particularly altitude, in the detailed enlargement on the right.  The line of the Cotswold escarpment forms the main eastern edge to the mistletoe area, whilst on the western side the valleys of the Rivers Wye and Usk can be traced as lines of mistletoe records, taking mistletoe towards the Welsh uplands. The northern boundary of the area is formed by the Clee Hills (north-west) and the Birmingham plateau (north-east). The central empty area is the upland area of the Forest of Dean – that mistletoe, despite loving trees, isn’t fond of woodland or higher ground.

The 1970s and 1990s Mistletoe Surveys

Much of what we know about mistletoe distribution in Britain comes from survey work co-coordinated by the Botanical Society of Britain and Ireland (BSBI) in the 1970s and a follow-up project, jointly run by BSBI and Plantlife in the 1990s. Data from both periods are shown in the small maps on the left.

The 1990s survey aimed to assess whether the decline in traditional apple orchards was affecting mistletoe too – was mistletoe declining? Results were mixed – orchard loss can affect mistletoe abundance (and vice versa as too much mistletoe kills orchard trees) but distribution patterns remained broadly the same as before and the species is certainly not threatened.  Indeed the new data suggest more mistletoe in the east and south-east, though that might reflect better recording effort more than real change – though there may be change in future, and it may have started already:

Is the distribution pattern changing?

An over-wintering male Blackcap taking a mistletoe berry in Gloucestershire
An over-wintering male Blackcap taking a mistletoe berry in Gloucestershire

In the last 10-15 years there have been several reports suggesting that mistletoe is spreading faster than it used to in Britain.  This is particularly noticeable in eastern areas, where established mistletoe populations, whilst often long-established, have previously seemed slow to spread as they are outside their climatic comfort zone.

Something is changing though – as many of those previously static mistletoe colonies are shifting. It could be subtle hints of climate change – computer modelling does suggest that mistletoe will head east with climate change. Or it could be something else.

One possibility is better spread of the seeds by Blackcaps, a bird species that is particularly efficient at spreading mistletoe. British Blackcaps migrate for the winter so they do not, usually, affect mistletoe here. But in recent decades continental Blackcaps have started overwintering in Britain, with many thousands now spending their winters here. Perhaps mistletoe is spreading more because of their activity.

So… is mistletoe rare or common in Britain?

Since the 1990s National Mistletoe Survey, which investigated whether mistletoe in Britain was threatened by the ongoing loss of apple orchards (its favourite habitat) there has been a public belief that mistletoe is threatened. It is, across the whole of Britain, generally rare, though locally abundant in some areas. But that’s not the same as threatened.  There is no evidence of a decline – indeed the most recent evidence suggests increasing populations.

Local decline due to apple orchard loss is only an issue in the south-west midlands where both mistletoe and apple orchards are abundant. There is certainly ongoing loss of both (mistletoe and apple orchards) in this area and that is an ongoing cause for concern – but it is merely a reduction in local  abundance not a threat to the species per se.

There are other factors to consider too, especially in areas outside mistletoe’s main range.  In those areas it is commonest in garden and parkland habitats, and unlike apple orchards there’s no threat to these habitats.  Evidence suggests mistletoe is increasing in these areas and habitats.

Plus there’s the management factor – in older apple orchards in the main mistletoe ‘zone’ some mistletoe-bearing trees are becoming so neglected that mistletoe is increasing dramatically. This is only a short-term gain though – those neglected trees are dying and will be gone, taking their mistletoe with them, within a decade or two.

Factoring in biodiversity and commercial issues complicates this further. The biodiversity value of mistletoe is considered relatively high, with several dedicated species relying on it. But it isn’t known how much mistletoe is optimal for these species – with some evidence that they survive well in isolated mistletoe colonies and might dislike crowded mistletoe-laden trees.

From the commercial angle the ongoing loss of mistletoe in apple orchards is significant, as most of the Christmas mistletoe comes from these sources (it is not usually abundant enough or sufficiently reachable in other habitats and hosts).

So, drawing general conclusions for the whole country is difficult.  There are several key points to consider, including;

  • mistletoe is rare or scarce in many areas – but not threatened
  • mistletoe is abundant, sometimes unsustainably so, in others.
  • there is a trend of increasing mistletoe growths and faster spread in some areas
  • the quantity of mistletoe in orchards can be huge but is, ultimately, declining as traditional orchards are lost. This does not apply to other habitats.
  • loss of apple orchards only really affects mistletoe in its core growing area
  • mistletoe distribution is not affected by apple orchard loss
  • mistletoe distribution may be changing
  • optimal quantities of mistletoe for maximum biodiversity is not yet understood
  • loss of apple orchard mistletoe will reduce the seasonal mistletoe crop

There are information sheets with information on these issues here:

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Other European mistletoes

Mistletoe (Viscum album) distribution in Europe (from Flora Europaea) – note how the detail of distribution in Britain is lost in this zoomed out view
Mistletoe (Viscum album) distribution in Europe (from Flora Europaea) – note how the detail of distribution in Britain is lost in this zoomed out view

In mainland Europe mistletoe is much more widespread, occurring across most of the continent and spreading eastwards well into Asia.

Distribution here also depends on subtleties of climate, and the absence of mistletoe in the Netherlands, northern Germany and most of Scandinavia reflect mistletoe’s climatic requirements.  Small colonies occur in those areas but, like the isolated eastern colonies in Britain, tend to be fairly static.

A complicating factor for traditional mistletoe, Viscum album, in Europe, is the presence of additional subspecies. In Britain we have Viscum album subspecies album – a plant that only grows on deciduous hosts.  But on the mainland this is joined by subspecies austriacum and subspecies abietis which only grow on evergreens (pines and firs respectively).

Plus, further south in Europe, some other mistletoe species begin to appear.  These are, briefly:

Red-berried Mistletoe, Viscum cruciatum

As well as those subspecies of Viscum album there is one other full species of Viscum in Europe – and that’s the Red-berried Mistletoe, Viscum cruciatum.  Apart from the berry colour this mistletoe is similar to the familiar white-berried species, and grows in similar habitats – often on Olive trees. In distribution terms it is very limited, being found only in Iberia, and mostly in Spain.

Yellow-berried Mistletoe Loranthus europeaus

The most significant other mistletoe of Europe is Loranthus europeaus, the yellow-berried mistletoe. This is particularly peculiar, in comparison to the familiar white-berried species firstly because it likes (actually prefers) oak trees as hosts – whereas the traditional northern species is rare on oaks – and secondly it is deciduous.  So, for this species at least, those special properties of ongoing life through the winter months, doesn’t apply – it loses its leaves at the same time as the host. This species has a wide distribution across central southern Europe.

European Dwarf Mistletoe, Arceuthobium oxycedri

The last of the mainland Europe mistletoes is another oddity – our only representative of the Arceuthobiums or Dwarf Mistletoes.  These are species with reduced leaves, almost holo-parasitic on their hosts and they are major forest pests in North America. Our species doesn’t cause much damage, not least because it only grows on Juniper trees and bushes. And it isn’t very widespread. occurring mainly around the Black Sea and parts of the Adriatic and Mediterranean.

Distribution of European Dwarf Mistletoe, Arceuthobium oxycedri
Distribution of European Dwarf Mistletoe, Arceuthobium oxycedri

Some other mistletoe species from around the World are described on the biology page here. 

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Biodiversity value of Viscum album mistletoe

Mistletoes all over the world have very interesting interactions with other species, and not just with their hosts.  Most also form miniature ecosystems of their own, with specialist birds, insects and fungi.  This page outlines some of the biodiversity value of mistletoe in Britain, with bird species at the top and insect species below. Links to some information sheets are given at the end of the page.

Mistletoe birds in Britain

There are two key background points to consider for European mistletoe with regard to birds.  Firstly it relies entirely on winter birds for berry, and therefore seed, distribution – so birds are essential.  Secondly the white sticky berries of Viscum album are not attractive to many birds – many ignore them as they are looking for red, orange, black or blue berries (mistletoe is the only native British species with white berries)  and even if they try them the birds are put off by the super-glue quality of the berry pulp.

So which birds do take mistletoe berries?  In Britain the answer is largely Mistle Thrushes, whose common name and latin name, Turdus viscivorus, hint at a mistletoe specialism.  Other thrushes – including Redwings, Fieldfares etc will also eat the berries.  Mistle Thushes, despite their name, aren’t really mistletoe specialists as they occur commonly across the country in areas with no mistletoe, where they will eat any berries.  Furthermore they’re not really very efficient at spreading mistletoe.  They usually swallow the whole berry, seed and all, excreting a mass of semi-digested berry pulp and seeds about 30 minutes later.  Some of those seeds, still sticky, may stick to a branch where they can germinate.  Most will not – often hanging uselessly below a branch.

A few other birds will eat mistletoe too, including Waxwings and a few other relatively uncommon species, but the most efficient mistletoe spreading species is the Blackcap.  These smart little birds only swallow the berry skin and pulp, wiping each seed off their beak before swallowing – and so they are much more efficient than Mistle Thushes.

Breeding Blackcaps in Britain migrate south for the winter, so they have not, traditionally, been a factor in mistletoe distribution in the UK.  But changing migration patterns in the last 20-30 years have led to first 100s and now 1000s, of migrant Blackcaps from Germany and eastern Europe visiting Britain each winter.  This huge increase in efficient mistletoe spreaders may be altering mistletoe distribution patterns in Britain

Mistletoe insects in Britain

Specialist insect associations are a common feature of mistletoes worldwide – and ours is no exception, with six species known on mistletoe in Britain.  All are considered rare and worthy of conservation, though actually very little is known about how common they really are – sampling insects on mistletoe is quite difficult so there are large gaps in the data.

Four of the six are bugs and some are rather obscure – including the psyllid bug Cacopsylla visci, which looks similar to many other species-specific psyllids.

The mirid bug Pinalitus viscicola is more distinctive, and has been known in Britain for over 100 years, living on mistletoe on various hosts and habitats across the country.

Another mirid bug Hypseloecus visci is ‘new’ to Britain, known only since 2003. Since its discovery here it has been recorded across mistletoe’s main distribution area and also further east, notably on lime and hawthorn.

Those first three bugs feed on mistletoe itself but the fourth bug, Anthocoris visci, is a predatory species, thought to feed on the psyllid. This species occurs across the country, on mistletoe on a variety of host trees.

Most conservation work on mistletoe invertebrates is directed at the Mistletoe Marble Moth, Celypha woodiana, as this is a Priority Species in the UK BAP a Species of Principal Importance in England under the NERC Act 2006. Known in Britain since 1878 it has larvae that live inside blister mines within mistletoe leaves.  A factsheet on this species is available from Butterfly Conservation.

Our last mistletoe insect is the mistletoe weevil Ixapion variegatum. This is another ‘new’ species, only known in Britain since 2000. The larvae live inside the stems of mistletoe, usually just below the terminal bud during the summer months, and on emerging as adults that bud (which is next year’s flower bud) often dies.

Information Sheets on birds and insects of Viscum album:

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