The common understanding of “extinct” is, well, “no longer existing as a species.” So therefore most people may think “extinct in Ireland” means “never found in Ireland.”
Looking into the species listed in Padraic Fogarty’s Whittled Away as extinct, and consulting the Red Lists which are among his sources, one does find that the picture is at times complicated. Is a species definitely extinct or not? This is relatively easy to establish for larger mammalian or avian avifauna. Though here still there are complications. Is a bird that formerly bred here in abundance but now occurs are a sporadic rarity blown in (literally) from elsewhere “extinct in Ireland?” It is obviously even harder to determine for marine species, and also for inverterbrates and plants, which can go “under the radar”
The point shouldn’t be if a species is absolutely extinct or not, the point should be the precariousness of whatever population may or may not remain and the overall picture. I have debated including the nightjar in these posts, which has undergone a precipitous decline, and have alluded to how close the corncrake has come to extinction in Ireland. Even if the corncrake is not extinct, it is highly confined now to a few areas of the country. And from a species whose nocturnal crex crex was an integral part of rural life, it has gone to one only a a few have heard.
Biodiversity loss shouldn’t be about extinction, with anything short of extinction being OK.
The above is prompted by the mud pond snail, omphiscola glabra. On the IUCN International Red List page
it is listed as Near Threatened:
Omphiscola glabra has been assessed as Near Threatened (NT) as, despite a widespread distribution throughout the Palearctic region, regional declines have been evident throughout its range due to continuing threats of habitat loss. This species is typically found in soft, nutrient poor waters with few other aquatic animals or plants. These include freshwater marshes, small ditches, temporary pools or seepages that dry up or significantly diminish in summer. These habitats were typically converted into productive agricultural land or improved visually for landscape reasons. Based on current evidence, a population decline of 20–25% was inferred over three generations (i.e., 15 years), with the species therefore nearly qualifying for a Vulnerable assessment under criterion A2, as causes of this decline have not ceased.
The species was listed as “of Special Concern” in Europe by Wells and Chatfield (1992) due to the levels of decline over the previous 20 years.
Further down the IUCN page we read:
Ireland (Northern Ireland & Eire): Regionally Extinct. In 1980 it was present in three locations. In the latest version of the Irish Red Data book it states ‘One of the rarest of Irish molluscs. A colony was reported from Ballymacar Bridge, Shelmaliere Commons, near New Ross, Co. Wexford. This site has now been drained and the colony destroyed.’ (Byrne et al. 2009)
The story is a bit more complex in terms of absolute extinction. On the Biodiversity Ireland page, I found a PowerPOint presentation by Maria Long and John Brophy from 2013
gives more context and the story. In 2010 it is recorded in Carrickavranty near Waterford.
Is it still there? My internet based research has not been able to confirm it. Perhaps an actual physical trip to Carrickavranty is in order.