A RARE example of the world’s largest species of slug has been sighted in the Isle of Man for the first time in more than a hundred years, revealing its woodland habitat to be one of the few remaining ancient forests in the island.
The news came to light after an ash black slug was discovered in a deep wooded ravine with mature oak trees near Glen Auldyn by Keith Alexander, a visiting British invertebrate expert.
The species, distinctive for its dark grey with a pale wavy crest running the length of its back, is rare but widespread in both Britain and Ireland, and can grow up to 30cm in length. More commonly they will measure 20cm, so this 15cm Manx specimen is decidedly modest.
Andree Dubbeldam of the Manx Wildlife Trust commissioned Mr Alexander for a study of molluscs in woodland areas. Experts in this field don’t often come to the Isle of Man, the main reason why this species of slug hasn’t been spotted in the island since 1905, also near Glen Auldyn.
The ash black uses large deadwood for protection, requires high humidity and feeds on lichens, moss and algae.
If the original woodland is cleared the slug will not move on and recolonise another area, it will simply die out. According to Mr Dubbeldam, the ash blacks have likely being quietly going about their business at Glen Auldyn for thousands of years. Slugs are hermaphrodites, having both female and male reproductive organs, but two are required for mating so this latest discovery is probably not alone.
Mr Alexander is now back in the UK studying samples for evidence other, much smaller molluscs that may paint a similar picture of the area.
Mr Dubbeldam said: ‘These relic oak and hazel woodlands are the island’s ancient woodlands, survivors of time when woodland had been cleared from most of the island.
Mr Alexander was very excited when he spotted the slug.
‘Along with a tiny chrysalis snail and the brown snail found in Ballure Glen and Glen Roy, we have identified several important relic sites.’
The Isle of Man was at one time a forested island, subjected to clearing over thousands of years as people adapted the land for agriculture. Plentiful rock for building and peat for burning meant pressure on the forests was not so high as in other parts of northern Europe, though uses for native trees included consumption of vast quantities of Hazel sticks for spitting herring.
More recently the Victorian habit of removing the ‘scruffier’ native trees, like the bushy hazel, and replanting the more aesthetically magnificent beech trees in places like Groudle Glen has seen the reduction and extinction of many native woodland plants due to the increased shade.
Mr Dubbeldam acknowledged that none of the 30 identified relic areas are under threat presently, but he would like to see a return of these altered habitats to their more natural state.
‘I would never advocate felling beeches, but perhaps as this generation begins to fail they could be gradually replaced with native trees,’ he said.
l Terry Cringle’s view, page 21