Rough Identification Guide to Slug Genera of Ontario (In Progress)

Guide to Superfamilies

When trying to identify a slug, here are some characteristics you should try to notice (in roughly this order of importance):

How much of the body is covered by the mantle
Location of breathing hole (pneumostome) on the right side of the slug, relative to the mantle
Shape (e.g. is there a keel/ridge on the tail behind the mantle or is it round)
Texture, especially on the mantle
Size
Colour and pattern (e.g. orange, brown, plain, mottled, stripes along the sides)
Mucus colour

By far the most common genera to see are Arion and Deroceras. Double-check if you think it is not one of those two. Also note that it is often difficult to determine species of slugs without dissection.

This guide only includes genera that I know to be in Ontario. It is unclear for sure what genera and species are present - hopefully iNaturalist can help improve our knowledge. I'd appreciate any suggestions or critique.

Superfamily Parmacelloidea

Has a strong keel running all the way from the mantle to the tail
Pneumostome toward back of mantle
Mantle can look like it has two different sections
Mostly plain colouration with little pattern

2 genera in Ontario (Milax, Tandonia) in one family

Superfamily Limacoidea

Rounded tail (no keel) except sometimes at very end of tail
Pneumostome toward back of mantle
Mantle texture often with circular ridges resembling fingerprint
Can have plain, mottled, or striped pattern

5 genera (Lehmannia, Limacus, Limax, Deroceras, Boetgerilla) in three families

Superfamily Arionoidea

Pneumostome usually either halfway along or toward front of mantle
If the mantle covers most of the slug (i.e. not just the front half, or it looks like it has no mantle), then it is in this superfamily
Pattern often striped, but can be plain or mottled