On a recent visit to Prince Rupert, my granddaughter and I encountered a Pacific banana slug (Ariolimax columbianus) slowly moving along a walking trail. This is a large (up to 10 inches long) native slug typically found in coastal B.C. forests west of the mountains.
It was a brownish-yellow colour, but they can be bright yellow (hence banana), greenish or reddish-brown, or even white. Some have irregular-shaped black spots all over the foot which can coalesce and make the slug completely black.
Slugs are snails in which the shell is completely lost or much reduced. To protect itself from dehydration and predation the slug must produce lots of slime.
A large part of the banana slug’s body is the muscular foot used for movement. At the front is a mantle that covers all the vital organs (lungs, stomach etc.)
The mouth and two pairs of tentacles are located at the front. The longer tentacles have ‘eyes’ at the tip for sensing dark and light, whereas the smaller ones are for feeling and smelling. The mouth contains a ribbon-like band bearing numerous ‘teeth’ and is called a radula.
On one side of the mantle is the breathing hole (pneumostome). The anus and genital pores open at the edge of the mantle.
Banana slugs are hermaphrodites having both male and female parts. Their sex life is very elaborate as they circle around, bite and lick each other, produce copious slime, and end up facing in opposite directions to each other in an ‘S’ position so that they can transfer sperm to each other.
Sometimes, they may get stuck together as the penis can enlarge to be huge. Then they struggle to part and one or both may end up biting the other’s penis off in a process called apophallation. A slug without a penis is then forced to behave like a female and can only produce eggs. Eggs are small, round, and semi-transparent.
Banana slugs are beneficial and are known as ‘nature’s garbage collectors’ because they keep natural forested ecosystems clean by consuming dead plant material, feces, dead animals etc.