Western Daily Press (Saturday)
A giant of the slug world
Gardeners may want to look away now, as Charlie Elder goes on the trail of the UK’s – and quite possibly the world’s – largest slug
As any gardener will testify, the mild and wet West Country is a paradise for slugs. Step outside once the light fades and a whole variety can be found motoring around tucking into our lettuces, razoring off flower seedlings and carving holes in our hostas.
However, if one is able to momentarily put aside the damage they can cause, it is worth appreciating the remarkable variety of these molluscs – some lemon yellow or glossy black, others delicately patterned or a ghostly white.
And they are not all after your veg. While the majority of our 40 species are generalist herbivores, some have a particular taste for fungi or lichens and only a small number are more widely considered a pest.
They also play an important role in ecosystems, acting as composters, disposing of decaying vegetation and providing slimy snacks for birds, hedgehogs, toads and ground beetles.
So, it’s three cheers for our super slugs! Hip-hip…
Or maybe I’m alone on that one. Being vulnerable to predation and desiccation, soft-bodied slugs and snails typically keep out of sight by day or in dry conditions, tucked away in cool crevices. But after dark a veritable army of these guzzling gastropods goes on the march.
If you want to go slug spotting (and I imagine that idea also being greeted with universal silence) then a damp night provides ideal conditions. And this month I set off on a slug hunt with a difference – in search of a monster mollusc found in our ancient broadleaf woodlands: the ash-black slug (Limax cinereoniger).
The ash-black slug is not only the UK’s largest slug, but also reputed to be the world’s largest land slug, with individuals typically 10-20cm long but apparently capable of reaching 30cm (that’s a staggering foot long) in parts of its European range.
However, fear not gardeners, your tender perennials are safe. This hefty forest slug is a tree-climber with an appetite for fungi and algae.
I have wanted to come across one of these critters for a while, given they can be found in old oak woods in the Westcountry, and I joined expert entomologist John Walters and acclaimed nature writer Brigit Strawbridge at a wood near Bodmin to try our luck.
It was a warm evening, with a breeze keeping the midges at bay, and as the light faded we headed into the shadows beneath the canopy and played our torch beams up and down the trunks of trees in the hope of spotting one heading out, and upwards, to feed.
I’ll admit, this was not the first time I had been on a nocturnal hunt for a forest slug. Back in 2018, I joined a citizen science expedition to Borneo in search of new species. The trip, run by Taxon Expeditions, enabled untrained enthusiasts like myself to team up with taxonomists, biologists and geneticists exploring tropical rainforest and recording new discoveries.
Our big find among many was a small and rather secretive slug, resulting in a published scientific paper in the Journal of Molluscan Studies in which we named the species after our triumphant ‘slug squad’ – Microparmarion exquadratus.
Slugs are far from abundant in the northern forests of Borneo, and this rarity was a type of
‘semi-slug’ – halfway between a snail and a slug, bearing a small vestigial shell on its back.
In fact, slugs are snails which have lost their shells, rather than the other way round, and possess a remnant of the absent shell, typically hidden out of sight beneath the thick mantle area on their back.
This month’s search in a Cornish wood was mercifully free of the risk of being bitten by tropical leeches or snakes that were plentiful during the humid night safaris in Borneo. But it was still every bit as atmospheric, and we came across one of Britain’s rarest beetles – the blue ground beetle, a large and leggy insect found at only a handful of sites and a nimble climber which preys on slugs (including tackling the mighty ash-black slug).
The conditions were perhaps too dry and slugs were keeping out of view, apart from the occasional large black slug. This is a decent-sized species, though the ash-black slug can be differentiated by a light ridge running down the bottom half of its back, while its underside is noticeably white along the middle and dark at either edge.
On a second trip I joined John
Walters in Devon Wildlife Trust’s Dart Valley reserve at the eastern side of Dartmoor, and once again we were not blessed with good fortune by the slug gods (imagine them if you dare). John, who is a wildlife artist and fantastic observer of nature, showed me the best area to search, and heading back we came across a couple of leopard slugs – which as the name suggests are light with blotchy dark patterning. They are another large species, with a keeled back like the ash-black, and feed on fungi and dead plant or animal matter using, as with all slugs, mouthparts bristling with thousands of tiny tooth-like protrusions called denticles.
Finally, this week I returned to the same wood at dusk and waited until darkness fell. Alone in an ancient woodland, silent apart from the sound of the nearby River Dart and quite a walk from the nearest road, certainly tested my nerve.
At around 11pm, as I searched the mossy bases and lower trunks of trees, I was brought to a halt beside a huge oak tree by a couple of hornets guarding the entrance to their nest.
Beneath them, curled among the roots, something else caught my eye in the torchlight – a large dark slug with a light dorsal line. Immediately I recognised it as the species I was after: an ash-black slug emerging for the night shift.
It was an impressive beast, gradually unfurling before making headway across a tree trunk, its two pairs of antennae extended – the longest pair sensitive to light and smell, while the smaller pair beneath working on touch and taste. At full stretch it was probably over 12cm in length.
For anyone who likes their wildlife, seeing a new species is always a treat. And given three attempts I had certainly earned my sighting of this localised woodland specialist.
More than that, the hunt had taken me into woods at night, which in itself is a magical experience, and opened my eyes to the fact that not all slugs are alike. At a safe distance from my lettuce, these serene wanderers going about their business after dark are really quite captivating.