By Sharon Hawley, Volunteer Nature Guide
After 15 years of leading school groups along the trails of Tryon Creek, I discovered that I could always count on finding one of these. What’s small, sticky, moves slowly, has a yellowish tint, and is sometimes covered with spots? You guessed it; banana slugs the often overlooked and under-appreciated, but vital recyclers of the forest.
What began as curiosity, has led to an ongoing study of some of Tryon Creek’s slimiest residents. It all started as I was preparing to present a special program for the park’s Ecological Explorations series (be sure to check here for future programs). I decided, after 15 years of guiding, to focus on the ever-present banana slug to enhance my understanding of these creatures that reliably show up on our walks. I did research over the winter, reading everything I could find on Ariolimax Columbianus, our native slug. I found research papers, mostly by scientists at the University of Washington and the University of BC, predominantly dealing with slug slime and movement. Wow, I thought. My background as a biology major helped somewhat with the terminology, along with a collection of several general interest books available, and so the slug study began…
Slugs, slugs, and more slugs
The next step was keeping 10 slugs in 3 containers in my house. I observed, photographed, questioned, and was often amazed. I hope you will be too.
First, take a look at their external parts. Note especially the long optical tentacles with eye spots, the breathing hole, or pneumostome (on the right side only), and the flexibility. Slugs are great escape artists, being able to flatten their bodies into and through tight spaces.
I photographed through the clear plastic of a clamshell container to get the views we do not usually see. This shows the underside of the head, and especially the top part of the mouth. On each side of the area we might call the neck is a glob of pedal slime, the stuff used in movement.
In their containers, my slugs ate a lot of lettuce, yams (which produced orange poop!) and cucumbers. I fed them every day. In the wild, slugs will eat all manner of vegetation, including some that has decomposed. They eat poop, as well.
It appears they poop out of their pneumostome (breathing hole). Actually, the anus is just inside.
In the diagram of the mouth, below, imagine being able to see their 27,000 teeth, or radula. When one nibbles on the dry skin on my finger, it tickles!
Internally, they have fairly well-developed systems for digestion and reproduction. Nervous, circulatory and respiratory systems are pretty basic.
I was especially fascinated by Slug Slime. Since many living things rely on mucus for a variety of purposes, and the banana slug produces an easily attainable and vast amount, they have been used in research.
Slime (or mucus) is vital to the banana slug. It is necessary for their mode of locomotion and adhesion. It protects them from predators. It maintains moisture in their bodies. It helps in reproduction.
The slime used in movement can increase traction (sticky) and overcome friction (slippery). It actually changes physically as the slug moves. When the muscles press down against the substrate, the slime liquefies, allowing the slug to glide. When the movement stops, the slime becomes sticky again, creating a “foothold” for other muscles to push against.
The muscles expand and glide, and then contract and stick, in a series of waves that appear to move forward along the underside of its body.
The body is never lifted off the ground at any point!
In Tryon, especially in the Spring, many young slugs can be seen. I noted these along the Cedar Trail.
They seem to like the waterleaf! I kept a couple inside during my research and they doubled in size in 5 weeks. The babies hatch from eggs that are about ¼ inch across and usually laid in clutches of 20 – 40. Parents do not care for the babies, who look like small adults almost immediately, with tentacles, and, very soon, spots. I have not found any eggs in the forest – YET! Next Spring!
Slugs are hermaphrodites, meaning each individual has both male and female reproductive organs. When they mate, both can become pregnant.
During the six weeks that I kept the 10 slugs at my house, there were 2 matings. I was able to get a minimum time fix on the 2nd one and was astounded that they remained together for at least 20 hours!
I will be continuing to observe slugs in the wild and hope you will too!
More Fun Facts about Banana Slugs:
Did you know?
They can’t walk backwards
They will numb your tongue if you lick them (and have billions of bacteria on their skin)
Glue can be made from slug slime
Tentacles can regenerate if lost
Slug “blood” is bluish
Some people eat them