As invertebrates, slugs do not have a backbone and are part of the approximately 96% of living things that are regarded as invertebrates.
Slugs are not a welcome part of most gardens and let’s face it, not many people’s minds go to . going back to take a closer look at the anatomical features of slug, because of their slimy soft bodies.
But these gastropod mollusks which are without shells are interesting little creepy crawlers and far removed from the large families of insect invertebrates.
In this article, we will also look at a few of the interesting features of slug and how to deal with them if they have set their sights on the fruits and veggies you have grown in your own garden.
The Slug Family Is a Large One
A “slug” refers to a land mollusc gastropod with an external shell or an internal shell.
Did you know? There are 48 slug species (with 40 present in the UK) but they all have an identical body structure, physiology and reproductive process.
Key Anatomical Features of the Common Slug
Being invertebrates means that slugs do not have a brain, spinal cord, musculoskeletal systems, or a cardiovascular system.
However, they can still express all of the characteristics of living organisms.
They have just adapted differently for breathing, moving, feeding, excreting, reproducing, and performing many more necessary activities.
Let’s look closer.
The Soft Elongated Body of the Slug Hides Some Interesting Anatomy
- Tentacles are the soft projections on the head of the slug that can retract. The two pairs of feelers on most land slugs are comprised of the two upward extending light sensing tentacles that have eyespots, as well as the lower pair extending downward for smelling, navigation, and possibly extending the distance from the slug’s body for light sensing.
- A Mouth. Believe it or not, slugs have a mouth, jaws and teeth which they use for feeding. Slugs have thousands of tiny teeth are arranged in a flexible band that is called a radula. These teeth act like the teeth of a circular saw, cutting into and rasping off food that the slug can ingest.
- The mantle is a saddle shaped structure, located behind the head on top of the slug. The anus and genital openings are located beneath the mantle. Their unusual location is because of torsion (see above), where most of the internal organs rotate through 180 degrees.
- Slugs only have one lung and to the right of the mantel is the pneumostome, which is a respiratory pore that the slug uses to breathe.
- The keel is a ridge found on some species of slugs, and runs from the anus, as the keel of a boat, through the length of the back to the tail.
- The tail is the remainder of the body of the slug, beyond the mantle.
- The foot is the flat rounded elongate bottom of the slug that it uses to propel itself when moving. The name gastropod means “stomach foot”. In some species of slug, there may be a crimping that occurs, referred to foot fringe. Slugs can move by the use of wave muscular contractions, allowing them to glide on their abundant slime secretions. The slime is secreted mucus, as will be noted below, and is secreted to protect and prevent injury to the foot.
- A vestigial shell can also be present, but is typically internalized and if present, it would be used as a store of minerals that the slug can utilize.
Though Slugs Do Not Have Backbones, They Still Possess a Competent Nervous System
Slugs don’t have a spine, and they don’t have a spinal cord, but they have a nervous system that uses the interconnected ganglia (collection of nerve cells, or neurons) that provide communication in the nervous system equally effectively.
The elongated axons ( where nervous system signalling and communication is necessary for breathing and respiration, locomotion, feeding, and stimulus reaction) of the nerve cells are responsible for what the slug is capable of doing.
Silvery Slime Trail You See on Your Patio after Rain Is Essential to a Slugs Survival
Slugs are mostly made of water and unlike snails lack a shell to protect them, so they are constantly in a losing battle against desiccation (dryness). Slugs keep themselves hydrated with a wet, mucusy discharge of water and mineral salts.
Slugs produce 2 types of hygroscopic, or moisture-holding, mucous:
- The first, a thin & watery mucus is distributed from the center of the slug’s foot to the edges of the foot. The mucus contains tiny fibres that provides traction as the slug moves, as well as molecules that can be detected by another slug, that they may be searching for a mate.
- The second which is more viscous, coats the entire body of the slug, which helps to prevent the slug from drying out. This mucus provides the slug with its distinctive sliminess and can also make the slug, a really slippery meal for the birds and other predators. The sticky slime can also serve a function in reproduction as the hermaphrodite slugs are stick together to exchange eggs and sperm.
Put Your Knowledge of Slug Anatomy and Physiology to Good Use to Tackle Pest Slugs Organically
To lower the amount of slugs feeding on the soft, leafy growth in your garden.
There are many basic methods you could use, that simply take advantage of the physical characteristics of the slug, to make your garden uncomfortable for them.
Some suggestions are:
Attract Slugs and Hand-pick Them
The easiest way to deal with slugs is just to take them off when you spot them. You could even make this job easier by collecting them in one area, and removing them all together.
Try This: Grapefruit skins, beer, old lettuce leaves and even pet food may be liked by slugs and can assist you to attract and trap them for future removal.
Target Slug Hiding Places
Since slugs need moisture they tend to hide out from day light in dark, damp places in your garden until the evening.
Don’t provide them with easy places like mounds of decaying leaves, old logs or boards, or upturned watering cans or planters.
A tidy clean garden will also expose them to their natural predators more than a garden with things to hide under.
Reach for the Table Salt
Salt is an oldy but a goody for getting rid of slugs.
It will virtually kill them. Salt has the same effect as drying them out extremely fast. You can use the salt to make a salt barrier around vegetable beds, and the slugs won’t cross that.
You can’t use too much salt, as it will kill the soil.
Create Physical Barriers
Coffee grounds can be used as a slug deterrent because they are an abrasive surface for the slug to inch over and they have caffeine in them that is a powerful neurotoxin.
Copper is also a powerful slug deterrent and is thought to cause an effect similar to an electric shock when a slug’s slime trail comes in contact with it.
Rounding Up
Slugs are most commonly considered pests because they chew on garden plants, fruits and vegetables.
Most of the work that slugs will do will be direct and beneficial work (ie. having to do with decomposition and biodegradation) for your garden.
Addressing the slugs in your garden with a curious and chemical free manner does take some extra work, but think of the benefits of a healthy garden ecosystem.