At 15.5 cms this is easily the biggest slug I have ever seen in the UK - and it was in my garden.... Oh dear!
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The great thing about Limax maximus is that it much prefers to eat rotting vegetation and mushrooms rather than green leaves. Not so bad for the garden after all
Lat/Lng: 51.072, -0.69
OS grid ref: SU918311
Outside the window of my house, in mixed broadleaved woodland, altitude 238m, oak, birch, chestnut and willow nearby.