On April 21st, 2011, the last attic vents went into a rebuilt stone lodge in Garryland Wood, just outside Gort in Co Galway. Less than a week later, two lesser horseshoe bats were hanging upside down in the attic, having entered the building the only way they are able: on the wing, just like birds, through an opening made just for them. This tiny species, unlike other Irish bats, cannot crawl, so small spaces are no good; they need clear openings, but for the last few decades, in old houses, outbuildings and sheds, we’ve been closing them off or letting the buildings fall down.
Garryland was home to 150 lesser horseshoes in 1975, but two decades later, the roof had come off and the bats had nowhere to roost, so the colony disappeared. As mitigation for the Gort-Tuam road scheme, the lodge was rebuilt with a slate roof, a cold room for winter hibernation, and warm structures in the attic that act as maternity boxes for mothers and pups. By 2016, 195 bats were living in the lodge, most likely having moved in from nearby roosts. In the summer of 2024, there were 304.
The lesser horseshoe is a miniature thing, weighing about the same as a one-euro coin. It hunts insects within a few metres of hedgerows while staying just a couple of kilometres from its roost. It is a creature of the dark – artificial light at night is an almost complete barrier to this species, acting like a closed door. For lesser horseshoes, the only light at night it can tolerate is the natural low illumination offered by the moon and stars.
There are about 15,000 lesser horseshoes in Ireland, and they’re a species of the west of Ireland. In Clare, Galway and Mayo, they hibernate in caves; in their stronghold of south Kerry, they winter in buildings. In north Kerry and west Limerick, there’s a “Limerick gap” where they are seriously struggling to survive because they’re homeless, agriculture has intensified, and light pollution is so severe.
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Last week I stood in a Limerick field owned by farmer Arnold Acheson, and he showed me a small “bat tower” he constructed beside his hedgerows for lesser horseshoe bats. This stretch of his land lies along the Mulkear river, which is a flight corridor for bats, and Limerick’s small population links the bats of Kerry and those of Clare. Boosting their population in this area is essential to ensure that the species is able to genetically mix across its west of Ireland range.
The tower is simple: a space with two open entrances (with a clever flap, known as a tilt tray, that prevents nocturnal predators like domestic cats from entering) and a series of rafters for the bats to roost. It was part of a publicly funded European Innovation Partnership project that ran from 2021-2023 – the first time agri-environment funding was aimed solely at this bat species.
In many ways, Ireland’s healthy lesser horseshoe bat population is largely down to the work of Kate McAney, who retired earlier this year after 35 years at the Vincent Wildlife Trust. She led roost surveys across the west of Ireland for decades, and established 12 reserves in four counties that are now home to about a third of Ireland’s entire lesser horseshoe population. With Ferdia Marnell of the National Parks and Wildlife Service (NPWS), she wrote Ireland’s first-ever national action plan for the species, and more recently she’s focused on solving the Limerick gap by mapping flight corridors, proposing buried winter chambers, working with Limerick County Council to address light pollution, and building new roosts on Limerick farms.
The hopeful thing is that if we build it, the lesser horseshoes will come. In Glengarriff Castle in Co Cork, the bats lived in the attic in the summer and hibernated in the cellars in winter, but the colony collapsed as the castle decayed. In 2006, the NPWS restored Flahive’s Lodge – a derelict building in the nature reserve – which was home to 50-60 bats. By 2007, 101 were counted, increasing to 318 by 2021. For their winter sites, the NPWS buried three precast concrete sections in an earth bank near the lodge, and by 2021, 373 bats were spending the cold months hanging upside down there.
[ We’ve been wrong about bats all along. It turns out they’re quite the wonderOpens in new window ]
The Limerick gap is a stretch of up to 70km that has been effectively closed to lesser horseshoes. There are no limestone caves to hibernate in, and Limerick has the highest density of street lights of the six counties; satellite data shows it is the artificially brightest of them all. If we can embrace the dark a bit more, and continue to support farmers to keep healthy hedgerows – providing the bats with essential cover from predators, and food like midges to eat – and pay them to build small bat towers, the doors will open to lesser horseshoes, and the Limerick gap might soon be filled.
