The grey squirrel is an object lesson in the value of public relations. Although regarded by many conservationists as little better than a tree-borne rat, the creature retains a loveable image with the human population at large. This is partly because of its cute, bushy tail, which distracts from the squirrel's multitude of sins. But it is also the result of the grey's policy of interfacing with the public at every opportunity.
The native Irish red squirrel is a recluse by comparison, preferring to stay in the trees. Meanwhile its brash American cousin runs amok on the ground, in parks, forests, and even back gardens. An indirect benefit of the grey's paws-on approach is that humans are often happy to supplement its already ample diet.
Like the Normans', the grey squirrels' arrival in Ireland was sealed by a marriage. In 1911, several pairs were brought here as a big-house wedding present and released into woodland in Co Longford. From there, they colonised the country with an efficiency that Strongbow and his followers would have envied, quickly driving the reds out of their ancient strongholds in the east. Not even Connacht is safe from these invaders. The Shannon was long considered a barrier, but the relentless greys crossed it eventually and are now advancing on Galway.
There is no evidence anywhere that the grey actively persecutes the red. The two can cohabit peacefully in the same woodland for up to 20 years. But the American species is bigger, more aggressive, and a lot less fussy about what it eats. Also, it spreads a virus - parapox - that appears to be fatal only to the red. With so many advantages, the invader inevitably prevails sooner or later.
It's not just red-fanciers who have it in for the greys. Foresters hate them because they wreak havoc on young trees. Sycamores are a particular favourite. The greys strip bark to get at the sap (a habit apparently picked up this side of the Atlantic - in their native grounds of the Eastern US they tend to be less destructive). And it's not just the bark. If you visit your local park after a storm, you may notice that the many short branch-endings scattered on the ground had been undermined by tiny teeth marks at the point where the wind severed them.
The native squirrel is now all but extinct in Dublin. Like another species shy of the public gaze - the multi-millionaire rock star - it appears to be confined to the leafier areas of two southside suburbs: Killiney and Dalkey. It exists nowhere else in the city, and certainly not on the northside. Even the Botanic Gardens is now an exclusively grey area, as is the adjoining Glasnevin Cemetery.
In the Phoenix Park, the grey squirrel only appeared for the first time in the same year as the Pope - 1979 - and yet by the late 1980s, the reds had disappeared from the largest city park in Europe. This may soon change. Just last week, a study began there aimed at reversing the trend. The plan is that a Dublin Zoo breeding project will attempt to retake the Phoenix Park for the reds, or at least establish a viable population. But first it has to find out exactly why they disappeared in the first place, a job that has fallen to Dr Tom Hayden of UCD's zoology department.
One of the things Hayden must try to establish is whether the park is "a net importer or exporter of squirrels". If the greys are "pouring over the walls", he says, re-establishing the reds might be like "holding back the tide". In the meantime, even to count the greys is a daunting task. No one knows how many squirrels the park has, or how the population is structured. Having to begin somewhere, the UCD team has begun by surveying the squirrels' signature: tree damage.
Hayden admits it is "almost a philosophical question" what you do with imported species that become naturalised. After all, most species in Ireland - including the rabbit, the rat, and the brown hare - were introduced here. This is one of the few countries in which there are more species now than a millennium ago, the UCD man points out.
But not everyone is philosophical about the grey squirrel's march. In England, where the reds have been driven to the margins - the Isle of Wight and Cumbria - the government has approved a cull of the aggressors. And the European Squirrel Initiative, which also advocates terminating them with extreme prejudice, has established an Irish branch.
On a not unrelated theme, it should be noted that an added advantage the grey squirrel has in Europe, unlike its home country, is that it is not regarded by humans as food. Even in the US, squirrel meat is a minority taste - most gourmets would rather eat their own toenails. But it can be used as a slightly gamier substitute for chicken or rabbit, especially in stews and casseroles. Squirrel nuggets, chowder, and southern fried squirrel also have their supporters.
For anyone interested, recipes are available in the cult classic The White Trash Cookbook, and other similar publications.