Slugs in Our Surroundings
Banana slug
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.
Banana slug
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).
Blue-grey Taildropper
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).
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Banana Slugs are native to the Pacific Coast of North America. They grow to be about 20cm (7.8 inches) and some have been measured at 25cm. They are the second largest slug in the world. To reproduce, Banana Slugs lay 20-30 eggs in a ground nest where they overwinter. The eggs hatch in the spring, and the baby slugs go off on their own. Banana Slugs can live up to seven years.
Banana Slugs need a temperate damp environment to survive, so are often founds in wetlands, coniferous rain forests and other similar habitats. They are found all along BC’s coast, but also stretch as far as northern California and southern Alaska.
The Banana Slug’s colours range from white, yellow, green, brown and black. They are often one lighter solid colour with darker splotches on their body.
Banana Slugs have a tooth-covered tongue used for eating, with up to 27,000 teeth (called a radula). They are decomposers, and help break down a wide variety of decaying plants, algae, mushrooms, deceased animals and even animal droppings. This decomposition is a very important part of maintaining ecosystem health.
Slugs produce a slime that keeps their body moist and helps them move easier. The slime, often considered gross to those who have touched it, is not poisonous and poses no threat to humans. Since ancient times, people have used the slime as a treatment for cuts and minor wounds.
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There are several different species of Black Slugs found in southern British Columbia. Their colour ranges from red to black to dark brown. All of them are native to Europe, and pose threats to the native ecosystems here as they eat several native places known to be species at risk. Fully grown, black slugs are about 18cm long.
Like the Banana Slug, black slugs have a wide ranging diet of live or dead plants, fungi, algae – and even other slugs. They will happily eat garden and farm plants too, which is why they are so often considered a pest.
Unlike the Banana Slug, black slugs can lay up to 150 eggs at a time which they bury in loose or shallow soil. They also reproduce very quickly which can cause their population to grow beyond manageable in a short time period.
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The much lesser known Taildropper slugs – genus Prophysaon – are native to the Pacific Northwest, and are considered a species at risk. Their numbers are dwindling due to loss of sensitive habitat they rely on for survival. They are very small slugs, sometimes only a few millimeters long.
The name tail-dropper comes from a defence mechanism this animal has, where it can self-amputate which causes a huge excess of mucous when attacked by a predator.
There are ten identified species of Taildropper slugs including the Scarlet-backed Taildropper, Reticulate Taildropper, Yellow-bordered Taildropper, and Blue-grey Taildropper.
The Yellow-bordered Taildropper has a distinct yellow border along its mantle. They are found in wet vegetation and wooded areas, often seen around Skunk Cabbage or other similar plants. These slugs have been found around Pacific Rim National Park, and Uclulet, BC.
The Scarlet-back Taildropper belongs to a family of slugs called Arionidae, or round-backed. They are about 2.5-5cm long, and colour varies from white to grey to red. They are found around the south coast including Saltspring Island, BC and are a species at risk, but not currently at risk of extinction.
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Habitat Acquisition Trust is working to increase awareness and conservation efforts towards the protection of this tiny, rare, local and extremely endangered slug. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has classified the status of the Blue-grey Taildropper as threatened, and its BC List Status is Red – extirpated, endangered, or threatened.
The Blue-grey Taildropper is very small, ranging from 5mm as a juvenile, to 4cm as an adult. Its colour is various shades of blue and grey. In the United States, Blue-grey Taildroppers have been found in Oregon, California, Washington and even Idaho. All evidence suggests that in Canada they are only found in 12 forests on southern and southwestern Vancouver Island, living in Garry Oak and Douglas Fir ecosystems. Both of these ecosystems are threatened and disappearing from human development and climate change.
Within these environments, the Blue-grey Taildropper slugs are most often found on the forest floor among leaf litter, Sword Ferns, Ocean Spray, and other moist plants and fungi. Like Banana Slugs, Taildroppers lay eggs in the fall which hatch as juvenile slugs in the spring.
Blue-grey Taildroppers play a vital role in spreading Mycorrhizal fungal spores from the food sources they eat. The relationship between these fungi and trees is vitally important to the survival of the forest, so it is important that Blue-grey Taildroppers are able to survive and continue their important work in the ecosystem.
By learning more about this amazing creature, people can become more aware of the threats it faces, and conservation efforts that can be done to protect it. Learn more about the Blue-grey Taildropper Slug here.
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