As far as I know the grey squirrel introduced in Germany by humans. It starts to slowly oust the common brown squirrel.

Of course I feel bad for the brown squirrel but people around here act like it's the end of the world. They say that it somehow matters for the overall habitat/natural environment. Does the growing number of grey squirrels and the according shrinking number of brown squirrels really effect the complete natural balance?

  • What's with the black squirrels? I also regularly see those in Germany.
    – Wills
    Commented Aug 17, 2016 at 14:01
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    They're just grays with a genetic mutation @Wills. Often seen in cities where the gene pool is limited
    – user2766
    Commented Aug 17, 2016 at 14:54
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    More info: en.wikipedia.org/wiki/Black_squirrel. I think the gene is recessive which is why it's more prevalent in particular groups.
    – user2766
    Commented Aug 17, 2016 at 14:55
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    I am sure someone has used that expression for this but generally that is used to describe the genetic competition within a species, not between native and alien species.
    – RomaH
    Commented Aug 17, 2016 at 21:56
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    @NoctisSkytower: maybe, but then that's always the situation with invasive species. Japanese knotweed appears to be the fittest plant in many habitats, but it doesn't follow that we actually want it to dominate... Commented Aug 18, 2016 at 9:53

4 Answers 4


Yes, they do damage habitats, namely from bark stripping, and disease. This is why the UK class them as a pest. However it is not limited to grey squirrels as red squirrels also strip bark, but they have much smaller numbers proportionally so their damage is proportional. Lack of grey squirrels therefore does not wholly prevent this damage.

In addition to displacing this native species they frequently cause damage to woodlands by stripping bark from the main stem and branches of trees

This has an effect commercially and natively. This can lead to a loss in food for red squirrels, birds, dormice etc.

Such damage acts as a major disincentive to the planting of broadleaved and coniferous trees for timber as it reduces the value of the final crop. Increasingly wider impacts are being recognised as potentially of major significance to woodland conservation, biodiversity and sustainability. In time damage may lead to a loss of particularly vulnerable species (e.g. beech) within the mature canopy of woodlands and this may be accompanied by loss of associated fungal and invertebrate fauna and their predators. In addition, there may be indirect competition, e.g. for food, between grey squirrels and native fauna such as the red squirrel and common dormouse; or predation by grey squirrels, e.g. on woodland bird populations. Grey squirrels also carry squirrelpox virus, an infection fatal to red squirrels.

The UK has been controlling the population of grey squirrels for many years, and we have some grey free areas, such as Brownsea Island.

Source: The Forestry commissions 2007's grey squirrel PDF

  • 3
    Greys are still encroaching on areas of the Lake District with reds, so overall the picture looks bad for the reds.
    – Chris H
    Commented Aug 17, 2016 at 10:19
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    You may want to emphasize that while grey squirrels can carry and transmit squirrelpox, it is mainly the red squirrels who die from it. Few infected grey squirrels can potentially infect and kill most of the red squirrel population in an area.
    – Peter1807
    Commented Aug 17, 2016 at 11:42
  • @Peter1807 I think that's clear form the last line in itself.
    – Aravona
    Commented Aug 17, 2016 at 11:56
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    You guys apparently need more weasels and raptors in the UK.
    – ShemSeger
    Commented Aug 17, 2016 at 14:12
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    Pretty much every natural predator to Grey squirrels is endangered in the UK. @ShemSeger Where there are Pine Martens (i.e. Scotland) the Red Squirrel population has bounced back. But these are (unfortunatly) no longer widespread in the UK
    – user2766
    Commented Aug 18, 2016 at 7:56

They say that it somehow matters for the overall habitat/natural environment.

Just to tack onto Aravona's excellent answer:

isn't losing a rare species to a very common species a bad thing in its own right?

Un-natural tampering in the diversity in an ecosystem has always been proven to be a bad thing (see examples below from Australia). Greys will effect the ecosystem in many different ways when compared to the smaller Red. Any (unnatural/man made) change in an ecosystem should be resisted.

On a wider context (i.e. not just squirrels). Introduction of foreign species to an ecosystem can be totally devastating, see rabbits or cane toads in Australia. The introduction of grays has had relatively minor consequences when compared to these issues.

So again, history teaches us that introduction of foreign species can have wide ranging and unforseen problems, so all introductions by man should be prevented. whether they have minor consequences or wide ranging and dangerous ones.

BTW this isn't natural selection, man has taken a species with natural checks and measures in it's natural habitat and transplanted it thousands of miles away into an environment without these checks. Likely (eventually) nature will catch up but humans influence these processes far too fast and it takes time for nature to re-balance.

As a side note to this, humans now influence their envrionment so much that it's thought we may now no longer be continuing to evolve! So humans and human consequences are well outside of natural processes.

Why are Grey squirels bad for the red?

The main issues with Grey Squirrels when introduced into a Red Squirrel population are twofold:

  1. Squirrel pox

    The Grey carries a disease (Squirrel pox) that the Greys have a genetic immunity to but the Reds don't. So if a population of Greys comes into contact with a population of Reds the pox is often spread killing the Reds but leaving the Greys unaffected.

  2. Competition

    Basic natural selection, the Greys are bigger, stronger, reproduce faster and eat more than the Reds. So the Reds lose out here, lowering their numbers even further.

The UK is an excellent case study in this. Reds used to be the only squirrel in the UK prior to the introduction of the Grey. They are now critically endangered with a population of only 140,000 (compared to 2,500,000 Greys) left. The future is increasingly bleak for the Reds in the UK with some major holdouts losing large numbers of individuals despite fierce protection and a shoot on sight policy for Greys.

For example the small population on the Sefton coast near me, lost nearly 85% of its population recently due to an outbreak of Squirrel pox. This is starting to bounce back but it's tough to bounce back from losing that number of individuals in short period of time.

  • But is the end effect on the environment any different despite the dominant squirrel species?
    – SeanR
    Commented Aug 17, 2016 at 11:20
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    The situation in Ireland is very similar to that in Britain. One way by which the invasive grey squirrel out-competes the native red squirrel is that the greys can digest food containing tannin and eat large seeds such as acorns before they have ripened (giving them a substantial head-start on the reds). reference.com/pets-animals/… Commented Aug 17, 2016 at 11:40
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    @AnthonyGeoghegan So the grey squirrels are an evolutionarily superior brand of squirrel - what's the problem
    – coburne
    Commented Aug 17, 2016 at 13:31
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    @coburne No. They are a different brand of species which wins against the reds under some specific circumstances. If after Squirrel pox, which kills all the reds, we get Grey Squirrel Pox that kills all the greys (and which the reds would have been immune to), then we have neither grey nor red. And without hosts even the Grey Squirrel Pox dies - so is "everything dies" the evolutionarily superior solution? A species can not be evolutionarily superior, it can only have a competitive advantage in a specific ecosystem which - geologically speaking - only lasts for a short amount of time.
    – Peter
    Commented Aug 17, 2016 at 14:22
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    @coburne No, they are an animal which has been plucked outside of evolution by mans interference and introduced into an environment where they are not meant to be. Nature simply hasn't been able to catch up (yet). There are numerous, numerous examples of devastation caused by this kind of interference, see rabbits or cane toads in Australia.
    – user2766
    Commented Aug 17, 2016 at 14:28

Excellent answers already; one point no-one has covered is that greys will occasionally eat eggs / chicks of small birds. Wikipedia says there is a lack of evidence on the actual impact of that, but it is something that does have a wider effect and that reds very, very rarely do.

However, there is, in the UK at least, also a reverse viewpoint. The introduced grey squirrels are greater generalists than the reds. Red squirrels thus suffer far more from habitat destruction and climate change than greys.

You often see greys bouncing along the pavements in my town, a city of 250,000 - they can live in parks or gardens and will coexist with humans and eat a wide range of foods; whereas reds are limited to conifer woods.

So another way of looking at it is that humans have depleted the red squirrel population by destruction of their specific habitat requirements, and the greys have filled the gap. The greys get a bad rap as invasive vermin, but we should really be looking at what we did that allowed them to become so dominant.

Britain’s surviving red squirrels feel the pressure (New Scientist)

However, reds do have some natural advantages; they have greater agility, enabling them to avoid pine martens, a major predator.

In neighbouring Ireland, the population of the less nimble greys crashed when pine martens became more abundant, while the reds were unaffected

Pine marten in search of a snack takes a selfie (New Scientist)

In answer to your actual question, in my view there is no straightforward answer. Liam's statement of "any (unnatural/man made) change in an ecosystem should be resisted" is a classic conservation viewpoint, but there are other ones, and once a change such as an introduction of an non-native species has occurred then any attempt to resist risks being an even more dramatic man-made intervention. Also, a species as successful as the greys will spread widely itself - at what point does their population growth into other areas become natural rather than introduced?

And of course, reintroduction attempts such as the UK beaver reintroduction blur the line - a reintroduction is clearly an unnatural change. Should we accept that a snapshot in time when beavers were a native species has gone, and conserve the current moment, or should we try to return to and conserve the past?

Grey squirrels have been in Britain since 1876; when do we start considering them just a highly successful endemic species?

DISCLAIMER: I am not an ecologist; I just have a fascination with ecology and have developed a recent interest in grey/red squirrels in the UK :o)

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    One small point: Reds are limited to conifer woods because of the grays, not despite them. They adapt (slightly) better in this environment than the greys not because this was their main environment prior to the grays arrival. It's simply their last hold out. If there we're no grays we may well have red squirrals in our towns and cities, they simply have never had the opportunity.
    – user2766
    Commented Aug 17, 2016 at 14:31
  • your points on when they become endemic and the beaver re-introduction are very good BTW
    – user2766
    Commented Aug 17, 2016 at 14:33
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    Also, I guess that although a pine marten is a major predator as far as an individual squirrel is concerned, there are too few of them to make much of dent population-wise. Commented Aug 17, 2016 at 15:20
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    Pine martens are endangered also. They are virtually extinct in most of England and Wales. The only significant population is in Scotland. Where as the Gray's are everywhere!
    – user2766
    Commented Aug 17, 2016 at 15:33
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    What the reds needs is my wife, who can summon them on demand. When we were honeymooning we'd been talking about how she'd never seen one. "So compared to the greys, how big are they?" she said. Instantly one ran across the road in front of us. "About that big" I replied, deadpan. Commented Aug 18, 2016 at 8:56

The premise of the question, i.e. the occurence of Grey Squirrels in Germany is at the moment wrong:

The NABU page on invasive species in Germany says:

Aktuell gibt es in Deutschland keine Hinweise, dass Grauhörnchen bereits freilebend vorkommen oder unmittelbar zu erwarten sind

so far, there's no evidence of free-ranging Grey Squirrels in Germany, nor does that need to be expected in the near future.

So if you see a squirrel with gray or black fur right now in Germany, it's actually a perfectly normal color-variant of the Red Squirrel*

You can distinguish Red and Gray Squirres regardless of fur color by the fur at the ears: Red Sqirrels have bushy fur on their ears (Pinsel literally paint brush in German), Grey Squirrels don't.

There is a wild Grey Squirrel population in Northern Italy (since about 100 years), and they are expected to arrive in Switzerland and France, soon, though.

Two reasons why Grey Squirrels have spread far more slowly in Continental Europe compared to UK and Ireland:

  • The North Italian Grey Squirrel population is not known to have squirrel pox.
  • In contrast to large parts of England, Germany has pine martens in suitable habitats, i.e. forests and even smaller woods and bushes (and sometimes even less suitable habitats like marsh lands in Schleswig-Holstein). The status is protected, but under hunting law (exception is North-Rhine Westphalia where it is highly endangered). Hunting statistics are overall increasing, even though hunting pressure/interest has been decreasing due to low prices since the 1980s**.
    Pine martens btw. don't need pines or coniferous trees, they do fine with broad-leaved trees or bushes. But they need them in sufficient density so they can go from branch to branch and don't need to touch ground. They very much prefer to cross roads or railway lines (or rivers) from tree to tree rather than on ground.

*Btw. the English name confusion Red vs. Grey Squirrel does not occur in German unless English texts got badly translated: they are [Eurasisches] Eichhörnchen vs. Grauhörnchen

**The Hunting statistics include roadkills.
It's not a very good surrogate marker for population since it will react to population: e.g. in NRW the hunting statistic was exclusively roadkill already in the 9 years before they were taken out of the hunting law; whereas in BW where population is classified as OK roadkill was only 1/3 in 2016. And of course roadkill increases with traffic.
But at least it gives some indication.

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