there's quite abit of variability within the Field Studies Council's AIDGAP series, and this is one of the best I've encountered so far.
layout and content are great.
at the front of the book there are a series of clear keys to the different slug families and their members, with illustrations, key features, colours and sizes, to help you track down species identities.
the body of the book contains entries for each species, including key identifying features, similar species, habitat and distribution, and impact on human plant growing. each entry is accompanied by scale pictures of adults (and sometimes juveniles), showing variability in markings and colours.
I found myself sometimes working from the key, sometimes jumping to and between species entries, and ultimately using a combination of both to get to better know some of the slugs I encounter.
I also found the book fostered in me a greater appreciation for slugs! and as someone who grows a fair bit of food, it enabled me to identify the - relatively few - slugs that were going to be munching on plants I didn't want them to.