MAMMAL NAMES | The Rat Trap:

The Many Misleading Names of Ireland's Rodents

The brown rat's Irish name, francach donn, derives from the mistaken belief that it arrived from France

Last month we were introduced to two of the rodents resident in Ireland, the red squirrel and grey squirrel, and saw how an investigation of their names reveals a dramatic story of invasion and domination, survival and resurgence. However, our close look at the various names for these two species also revealed that some of these can be somewhat misleading, and this month it will become clear that the same can be said of many of the other rodents on the island, especially their most reviled members – the rats. Among the accusations that can be levelled at these names is that they can lead to confusion over where these rodents live, who they are, and where they come from, while also making it possible to mix some of them up with other mammals on the island. These names, then, are in essence a trap waiting to ensnare the unwitting, but by treading a careful path and looking at the names of each of these rodents in turn, we can avoid springing the catch.


Setting out on an investigation of the rodents’ names, a person could easily be duped into expecting that this might be a voyage through calm waters as the name ‘rodent’ itself couldn’t be clearer in its meaning. ‘Rodent’ simply comes from the Latin word rodere, meaning ‘to gnaw’, referring to the incisors that all rodents, including those in Ireland, possess, which they use to gnaw on everything from seeds to bones to bread. Because these incisors are ever-growing, rodents have to gnaw continuously, and so this is why mice or rats can do untold damage if they invade a house in Ireland, gnawing on timbers, plasterboard, and electrical wires.


So far so good, then, and as we meet our first rodent species things initially look quite straightforward too. The house mouse is surely one of the most familiar rodents to the people of Ireland, not least because, as was just mentioned, we often share our homes with them, even if this is an undesired cohabitation, at least on our part. The ‘house mouse’ is a very suitable name for this little rodent, then, and its Irish name, luch thí, means the very same thing, as does its scientific name, Mus domesticus, with mus, as we already saw when looking at Ireland’s mustelids, being the Latin for ‘mouse’, and domesticus needing no further explanation.


The scientific name for the house mouse would seem to be as straightforward as the English and Irish names, then, but actually it is here that things get a little more tricky and possibly confusing. Although some consider the mice in Ireland to be one of four species of house mouse found across Europe, Asia, and Africa, others hold that there is only one species, Mus musculus, split into four subspecies, making the scientific name of Ireland’s house mouse Mus musculus domesticus instead. And this results in quite a funny name for this diminutive rodent. As musculus is formed of the word mus, for ‘mouse’ and –culus means ‘little’, Mus musculus domesticus essentially seems to translate as the ‘little mousy mouse of the house’, which sounds like the beginning of a children’s poem.

The 'little mousy mouse of the house', Mus musculus domesticus

It is also worth noting that, although the house mouse generally deserves its name, rarely venturing far from buildings and spending the winter indoors, during the summer it ventures out into fields and hedgerows that lie close to buildings, while on uninhabited islands it seems to favour living in open-field conditions. Not always a ‘little mousy mouse of the house’, then.


The house mouse, of course, is not the only mouse in Ireland, and it shares the island with the wood mouse which is about the same size but has larger ears and eyes and a less scaly tale. And, as its name suggests, the wood mouse does not have as close a relationship with the humans of Ireland as the house mouse. Indeed, it is from this very aspect of its nature that its scientific name, Apodemus sylvaticus, is derived, Apodemus coming from the Greek apo, meaning ‘away from’, and demos, meaning ‘people’, while sylvaticus comes from the Latin and means ‘of the woods’.


Even more so than with the house mouse, though, the name wood mouse does not really capture how adaptable this rodent is, and though it is certainly found in woods it is also present in many other habitats, in everything from hedgerows to heather, cropland to grassland, blanket bogs to sand dunes, and even gardens.

Despite its name, the wood mouse is found in far more habitats than just woods

It is the Irish name of this rodent, though, that could truly lead one astray and result in it being mixed up with an even smaller mammal from an entirely different order. The wood mouse’s name in Irish is luch fhéir or luchóg fhéir, with luch, as we have already seen, meaning ‘mouse’ (luchóg just means ‘little mouse’), while fhéir derives from the word féar, meaning ‘grass’. So, the wood mouse is, in Irish, the ‘grass mouse’. The problem here is that one of the Irish names for the pygmy shrew, which is not a rodent but more closely related to Ireland’s hedgehogs, is also luch fhéir or luchóg fhéir, so there is no way of knowing which one of these mammals is being referred to when the Irish name is used alone.


Also, to add to the confusion, in Ireland the wood mouse is also sometimes called the field mouse. But there is another rodent on the island that can also claim this designation, despite it not even being a mouse, although it is closely related to them. This is the bank vole, an even more recent arrival in Ireland than the grey squirrel, thought to have stowed away in earth left in the buckets of diggers and excavators that were sent to Ireland from Germany by the engineering company Siemens in 1925 when they were building the Ardnacrusha dam on the River Shannon. The name ‘vole’ comes from the term ‘vole-mouse’, the ‘vole’ part of this probably derived from an Old Norse word völlr, meaning ‘field’, which, in another neat connection with Germany, is thought to derive from the Proto-Germanic word walthuz.


If the names of the smaller rodents in Ireland can sow confusion, though, those of the larger members of their order on the island can be, if anything, even more confounding. There are two rat species currently scurrying through the dark places in Ireland: the brown rat and the black rat, and, as with the other rodents, an initial inspection of their names seems to reveal nothing but clear and accurate information about them.


For instance, the brown rat is also known as the common rat, which is fitting as it is found everywhere on the island, much to the dismay of many people who come into contact with it. And this description of the brown rat as common couldn’t be more true when it is compared to the black rat which is now one of the rarest mammals in Ireland, being found only on Lambay Island, which is about four kilometres from the Dublin coast, although it also turns up around ports every now and then. Indeed, its maritime connections are signified in its other name, the ship rat.


However, from here we veer onto a familiarly confusing path, that can lead to misidentification and misunderstanding. For example, the brown rat and black rat are not as different in colour as their names might suggest, an issue we also encountered when looking at the red squirrel and grey squirrel. The black rat actually varies in coat colour from being completely black to being brown with a light underside, while the brown rat, although usually a grey-brown colour, can also be completely black. Despite their names, then, colour is not a reliable way to tell these two rat species apart, and an identification should really be made on the basis of form as the brown rat can be up to twice the weight of the black rat and has a shorter, thicker tail.

Diagram showing the clear differences in form between the black rat and brown rat

If the English names of these two rats are misleading, though, the scientific and Irish names only serve to muddy the waters further. The genus that both rats belong to is Rattus, and there are no problems here as this is simply the Latin word for ‘rat’. Indeed, there are no issues with the scientific name of the black rat at all, which is Rattus rattus and so just means the ‘ratty rat’. However, when we get to the scientific name of the brown rat we embark on a voyage through a sea of mistaken beliefs that include the bases for the Irish names for the two rat species too.


The scientific name for the brown rat is Rattus norvegicus, a title that was erected due to the belief at the time it was named that the brown rat came from Norway. However, it is now thought that this species made its way to Ireland on ships that arrived from Russia or eastern Europe in the early eighteenth century, more specifically around 1722, and within a decade it had already become the bane of many peoples lives in Dublin, while its arrival also set the black rat on the path of precipitous decline that has brought it to such a parlous position today.


If the brown rat’s scientific name places its origins too far to the northwest, though, its Irish name places them too far to the southwest. The brown rat’s Irish name is francach donn, meaning ‘the brown French one’, which derives from the belief that the brown rat arrived in Ireland from France possibly during the Norman invasion. This name, then, is not only inaccurate by hundreds of kilometres but by hundreds of years.


As for the black rat, its Irish name also stems from the belief that this rodent arrived in Ireland from France, being francach dubh, or the ‘black French one’. However, where it actually came from doesn’t appear to be very clear. The earliest evidence for its presence in Ireland comes from a site in Rathmullen in Co. Down which dates to the early Christian period, which is generally held to begin in the early fifth century AD. However, a 2014 study has stated the date for the introduction of the black rat to Ireland as being 1,700 years ago, which would be around 300 AD, about a century earlier than the lower boundary of the early Christian period. And as the black rat is thought to have arrived in Britain during the Roman occupation of that island, and the Romans were still present around 300 AD, perhaps it made its way to Ireland from there. In any case, there appears to be little evidence to suggest it arrived from France.


Whatever the truth about where it invaded the island from, it seems to have declined and gone extinct in Ireland and the rest of northern Europe in subsequent centuries before reappearing again in this region in Viking times, apparently due to the new trading routes opened up by these great seafarers. Strangely, though, it has not been found in Irish Viking sites, although it did become re-established in Ireland a little later, certainly by the eleventh and twelfth centuries, and from this time became common and widely distributed on the island. However, yet again, it is not clear where this later wave of black rats to colonise Ireland came from, so we cannot assume they came from France in this instance either.


The Irish name for the black rat, then, is, if anything, even more misleading than its English name. In fact, though the English name may be somewhat misleading when it comes to coat colour, in another manner the name black rat would appear to be devastatingly accurate, as this rodent has some very dark connections indeed.


For a long time, the black rat has been blamed for unleashing an age of lament in Ireland, as it is thought to have transported a tiny mass murderer to this island, the fleas in its coat harbouring the bacterium Yersinia pestis that causes plague, which is thought to be responsible for the Black Death that claimed 25 million lives in Europe, over a third of its population, between 1347 and 1353. The Black Death first appeared in Ireland in 1348, and plague devastated Irish towns a number of times up to the middle of the seventeenth century, with the loss of countless lives.


However, it now seems that even when it comes to this connection that the black rat is not as black as it has traditionally been painted. A study published in January 2018 found that the Black Death and the many other outbreaks of plague up to the nineteenth century, collectively known as the Second Pandemic, were likely not transmitted by the fleas in the coat of the black rat but by fleas and body lice on humans.

Flea infected with Yersinia pestis (L) and 14th century illustration of Black Death burials (R)

In any case, this last connection as regards the names of Ireland’s rodents provides us with some sobering perspective. Although we might find the names of Ireland’s rodents a frustrating obstacle to understanding them at times, this is no matter of life and death. In fact, perhaps we should not see these names as a trap waiting to ensnare us at all but as the wrapping on a present, temporarily obscuring our view yet begging us to delve deeper to see what truly lies beneath.

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