Monthly Archives: November 2014
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
Hailstorm: The Aftermath
By Bruce Rottink, Friends of Tryon Creek Volunteer Nature Guide and Retired Research Forester
This past June 16th a violent hailstorm hit Tryon Creek State Natural Area. Many plants in the forest sustained damage, but was it serious? How would the plants fare in the long run? What can we learn from this experience?
Some plants are tough!
Let’s take a closer look…
The most common type of damage was the shredding of plant leaves, and breaking of stems from the impact of the hail stones. In general, the leaves and stems that were going to die from hail damage, died quickly. For example, the severely injured leaves on the red elderberry (Sambucus racemosa var. racemosa) shown below were already grey-brown and crispy within two weeks after the hail storm.
The leaf shredding looked serious, and certainly didn’t do the plants any good. But, many of the “shredded” leaves persisted throughout the season. Two species that showed especially severe leaf damage were trillium (Trillium ovatum) and thimbleberry (Rubus parviflora). The photo below was taken 34 days after the storm. It shows a trillium “leaflet” which was brutally shredded by the hail. It hung on like this throughout much of the summer, finally turning brown on approximately a normal schedule.
Likewise, the photo below is a thimbleberry leaf taken exactly 5 weeks after the storm.
The persistence of the leaf tissue in spite of the shredding, is a testimony to the effectiveness of networks. The leaves of broad-leafed plants are typically based on a vast network of veins.
What do these veins do exactly?
A) physically support the leaf
B) deliver water and minerals to the leaf’s cells from the roots
C) carry carbohydrates (“food”) produced by the leaf to other parts of the plant
If you guessed A, B, and C, you’re correct! The key is that there are more than one vein serving each small chunk of the leaf. Thus if any one of the veins was broken by hail, water and minerals could be delivered to a specific cluster of cells via a different path. This network makes the leaf very resilient. The photo below is a close-up of the network of veins in a jewelweed (Impatiens capensis) leaf.
Just for fun, on the picture below trace the number of vein paths you can find to get from the major vein shown in the photo to the cluster of cells marked with the red star. (Hint: The first four ways are pretty easy to find.)
The other major kind of impact damage was the breaking of stems and petioles (a petiole is the “stalk” of the leaf blade which attaches it to the stem). There were many amazing examples of stems and petioles that were broken, and yet survived. The broken petiole pictured below is on red elderberry.
However, the leaf beyond this break remained green and alive, as pictured below.
Some plants have a backup plan!
Some plants sustained irrevocable heavy damage, and resorted to their “Backup Plan” which is to replace the parts that were lost with new parts. Two of the many plants that used this strategy were the skunk cabbage (Lysichitum americanus) and red elderberry.
The hail was particularly hard on the skunk cabbage. In the photo below you can see a skunk cabbage plant taken 23 days after the hailstorm. The blue arrow points to a severely shredded skunk cabbage leaf’s midrib, and the red arrow shows a new leaf sprouting after the hailstorm. This leaf was not visible 4 days after the hailstorm. To be honest, I can’t say for certain this leaf would not have sprouted up without the hailstorm; however the fact that the skunk cabbage had not produced any new leaves for many weeks before the hailstorm suggests that this leaf is indeed “a child of the hailstorm.” At the time of this picture, the new leaf was 15 cm (~6 inches) tall, but being nearly vertical makes it look less impressive. By mid-September, the new leaf grew to 32 cm (just over one foot) tall. A second post-hailstorm leaf appeared later, and grew to 9 cm (about 3-1/2 inches) long. Both stayed green longer than the leaves present at the time of the hailstorm.
The elderberry plants exhibited a classical response to the destruction by the hailstorm, as illustrated in the photo below. As you can see, the tip of the elderberry shoot has been knocked off. In each leaf axil (the crotch between the leaf and the twig) there is a bud. Normally, the tip of the plant produces a chemical, auxin, which inhibits these buds from growing, and they would only sprout out the following year. However now that the tip of the plant has been knocked off, there is no more auxin to inhibit those buds. They are more likely to sprout immediately. For the elderberry, the recovery strategy, then, is to have buds which were being held for next year open early.
The bud (red arrow) on the left side has not sprouted, but the bud on the right side has sprouted, which is facilitated by the death of the leaf (blue arrow) on that side of the stem. If you view the growing shoot tip as “the leader”, this is the botanical version of
“the king is dead, long live the king”.
Another interesting example of recovery from buds was Pacific waterleaf. The visible Pacific waterleaf shoots originate from a rhizome (essentially an underground stem). While there was no real recovery of the damaged above ground shoots, fresh new shoots from the rhizome appeared in many, but not all locations where the aerial shoots were severely damaged. At those sites where new shoots did not appear, perhaps the Pacific waterleaf decided to save its buds, and energy, for next year.
And for some plants, it’s the end of the line!
Some plants never did recover from the hailstorm. The best example is the jewelweed, an annual plant that grows mostly along the creek. The two jewelweed plants pictured below had their tops broken off, and were stripped of all leaves. While the stems managed to stay alive throughout the summer, this is not recovery!
As annual plants that must start from seed each year, jewelweed did not have buds already formed for next year which it could call upon to elongate early. As mentioned in my earlier Naturalist’s Note, the jewelweed will have to rely upon two things; the fact that viable jewelweed seed can be “banked” in the soil for a couple of years, and the fact that not all the jewelweed plants were damaged as heavily as these two individuals.
From an overview perspective, there were substantially fewer jewelweed flowers this year than the last two years. Only more time will tell how serious this setback was for the species at Tryon Creek.