Black Slug Invasion

TheTamshee says: Is there some mysterious "garden" plot to have the earth taken over by the Black Slug. These pests can grow up to 20 cm in length. Their colour is very variable - white, red, orange or grey are all common although black is most usual, often with an orange fringe. There is no keel, and the skin is coarse and granular. The sole is pale, sometimes orange, and the mucus is white. The black slug may rock from side to side when disturbed! Familiar to all gardeners because of its spectacular size, the black slug is rarely as destructive as other smaller species but can cause damage in spring to seedlings of many kinds. Later, when its preferred diet of rotting vegetation, fungi, manure and even dead animals is more readily available, it causes little damage in the garden - other than promoting heart failure if you step on one when chasing the neighbours cat from your prized veg patch.