It’s a lovely fall day. The sun is shining, the birds are singing, you’re out for a walk in the forest. As you’re admiring the colours in the trees and the smells in the air, you suddenly notice something on the ground that would cause many people to jump back and make a wide berth. Can you see it? In the middle of the path, trailing tree needles and forest detritus behind it is a long, green, slug. What is your reaction?

                Many people see slugs as pests who destroy gardens, and are considered gross due to the slime covering their bodies, and the slime trails they leave behind them.

                Slugs are not harmful at all to humans. Touching the slime, while an unusual texture, is not toxic. They are natural decomposers, helping with the decay process in forest and wetlands, which is a critically important part of ecosystem health. But as with many other plants and animals, the benefits of our local, native species are outweighed by the consequences of their invasive cousins.

              Slugs are living animals which are invertebrates – no bones. Along with snails they belong to the class Gastropoda, and the phylum Mollusca (Read more here). While many molluscs have a soft body protected in a hard shell, slugs evolved so their shells became either greatly reduced in size, or were lost completely. What remains of the vestigial shell is called a mantle, which looks like an extra layer of skin over the slug’s upper body. Within the mantle are the slugs reproductive and digestive excretion organs. Slugs breathe through an opening in their body called the pneumostome, which leads to the lung inside their body. Slugs have four tentacles on their head – two longer ones one top for sight and smell, two smaller ones underneath for touch and taste. The back of the slug is called the foot, and the
underside is called the sole. Some slugs have a fringe along the lower edge of their body, called a skirt (See here).

                As of 2021, E-Fauna BC estimated there to be about 94 species of terrestrial – meaning living exclusively on the land – slugs and snails in British Columbia. Of these 94, at least 26 are known to be invasive species originating in Europe, most likely carried in and spread around in imported plants (E-Fauna BC). There are also a large number of water dwelling invertebrates that are related to or look like land slugs and snails called nudibranchs.

          The most commonly seen and known slugs around southern Vancouver Island are the green Banana Slugs, which are a native species, and various species of black slugs, which are invasive. A lesser known group of native slugs which are endangered and considered at risk are the native Blue-grey Taildropper slugs (Click here for more information from HAT).

Writting by HAT volunteer Darcy Harnadek

Learn More

Gastrods - Britannica

The Land Snails of BC - E-Fauna BC

Slug Anatomy 101 - Oregon State University

Banana Slug - Go Hiking

Banana Slug - Sierra Club BC

Black slug - BC Invasives

Taildroppers - Island Nature

Scarletback taildropper - South Coast Conservation Program

Blue-grey taildropper slug - COSEWIC

Blue-grey taildropper slug - HAT