The Large Black Slug

Slugs are not as black as they are painted.  The Large Black Slug can of course be black but it also appears in another orange version.

  Although it can chew the odd bit of garden produce it is more interested in other stuff.  It's the much smaller common garden slug, the grey keeled slug, the grey field slug and the yellow slug that cause the most damage.

There are about 30 species of slug in the UK of which only those four can be considered pests.  It is estimated that the average garden has about 20,000 individual slugs and agricultural land will contain 250,000 per acre.  They mostly live underground and come out at night, using their slime trails to find their way back home.

Like snails, slugs have two long tentacles which they use to smell and dimly see, plus two shorter tentacles below, with which they feel and taste stuff.  In the photo above you can also make out the thicker 'mantle', the smoother bit just behind the head.  When they are alarmed they pull their tentacles in safely under the mantle.

This DEFRA site shows the 11 most common slugs   

 Defra slug identification

And this 23 page website, includes more details if you are really keen.

Identifying British slugs