Have you ever wondered why slugs and snails have tentacles on their heads that move around as they crawl along?
Slugs and snails have two pairs of tentacles or antennae that act as sensory organs, much like your eyes, nose, and tongue. The two longer upper tentacles are used for seeing and smelling the world around them. The two shorter lower tentacles are used for smelling and tasting.
Slugs and snails have many interesting ways to find their way around and survive without arms or legs. Let’s take a look at how their tentacles have adapted to keep them alive and safe, and what happens when they lose a tentacle or two in an attack.
Two longer upper tentacles for seeing and smelling
The tentacles higher up on a slug or snail’s head are the longer tentacles. There is a light-sensitive eye at the tip of each long tentacle and cells in the tentacle that can smell.
These tentacles have changed quite a bit over time…
All snails started out living in water, and many snails still live in water. Water snails have only two tentacles on their head (not four like land snails), with eyes at the base of these tentacles. With their eyes fixed firmly to their head, water snails have a very limited range of view.
Over a long period of time, some water snails adapted to live on land. As these snails adjusted to living on dry ground, their eyes moved from the base of their tentacles to the very tips of their tentacles and their tentacles became retractable (more on that a little later).
With eyes at the tips of their long tentacles, snails can move their tentacles to see much more around them. The upper tentacles can also move independently, which means that one tentacle can point in one direction and the other tentacle can point in another direction.
All of this movement is important because land snails crawl a lot further than water snails, so they need to see more and watch out for more dangers, like predators who want to attack them.
Once land snails learned how to live on land successfully, some of these snails evolved again – into slugs. Over time, evolving land snails grew smaller shells (semi slugs), or made their shells so small that they are hidden under the skin on their backs or disappeared completely (slugs).
So some water snails became land snails and some of these land snails became slugs. As a result, slugs and land snails are very similar and use their tentacles in pretty much the same way.
How slugs and snails use their tentacles to see
Slug and snails’ eyes are quite well developed, with a retina, lens, and optic nerve, like there are in human eyes. But slugs and snails don’t see like we do because they don’t have the same eye muscles or cells in their primitive brains to interpret what they see.
As far as experts can tell, slugs and snails can’t adjust their pupils to focus on things near and far, so things far away and nearby are probably very blurry for them. They also can’t see colors.
But we do know that slugs and snails can see changes in light, which tells them when it’s day time for sleeping and night time to come out, and when the days are getting short enough for snails to go into hibernation.
With such bad eyesight, how do slugs and snails see where they’re going?
Slugs and snails use their upper tentacles to see what little they can, but they “see” better by touching things with their tentacles. When they do this, they feel where they are, where they’re going, and they learn their way around an area. They also use smell for this, which we’ll talk about in a bit.
If a slug or snail touches something with its tentacles that it doesn’t like or that might attack it, the slug or snail pulls its tentacles back into its body for protection.
This pulling in of the tentacles is called retracting, so slugs and snails can draw back and hide their tentacles whenever they want.
The following video shows a snail waving its tentacles around to find out what’s going on and how the snail retracts its tentacles when they are touched:
How slugs and snails use their tentacles to smell
Slugs and snails can’t hear and they can’t see very well, but they can smell extremely well using their tentacles. In fact, smell is their strongest sense.
As slugs and snails wave their tentacles around, they are actually smelling chemicals in the air.
Odors are made up of chemicals, and each odor has its own mix of chemicals that make it unique. For example, your brain knows the different chemical odors between bread baking in the oven and rotten meat. Your nose picks up the chemical odors in the air, asks the brain what it is, and you react based on what your brain tells your body to do. One smell makes your mouth start watering and the other makes you turn your face away in disgust.
When odor chemicals come into contact with the olfactory (smelling) cells in a slug or snail’s tentacles, the olfactory cells send a message to the brain to interpret what the odor is – is it food, danger, or perhaps even another snail to mate with?
The brain decides what the odor is and gives the snail instructions on how to react, so the snail knows if it should follow the smell for food or a mate, or change direction to crawl away from danger.
Two shorter lower tentacles for smelling and tasting
The shorter tentacles that sit lower on a slug or snail’s face are used to smell, feel and taste things. They support the longer tentacles above.
The shorter tentacles don’t move around as much as the longer tentacles. They usually point to the ground to do their sensory work.
The shorter tentacles are used to:
- Taste food that the snail has found, to see if it’s edible
- Learn their surroundings, so a slug or snail can feel its way around even with bad eyesight
- Follow mucus trails left by the slug or snail, so the slug or snail can follow the paths it makes back to its shelter to sleep or to the food it eats every day
- Follow another slug or snail’s mucus trail, either to find and eat the slug or snail (if they are predator snails), to eat food with them as snails are social eaters and like to eat in groups, or to mate with them
- Sense danger, such as smelling a predator
Because all four tentacles on a slug and snail are used for smell, it’s often said that a slug or snail has “four noses”. These aren’t noses like people have or snouts like many animals have – they are four tentacles that use olfactory cells to smell things around them and mainly find food.
How slugs and snails retract their tentacles
Land snails and slugs can pull their tentacles back into their head. This is possible because they have a special muscle in their tentacles, called a retractor muscle, that they can control and they can pump blood into their tentacles at will.
When a slug or snail wants to pull a tentacle into its head, it tightens the retractor muscle for that tentacle. When the retractor muscle tightens and contracts, and blood is driven out of the tentacle, the tentacle gets shorter and shorter until it disappears inside the head.
When the slug or snail wants to push the tentacle out again, it pumps blood into the tentacle. As blood is pumped into the tentacle, it keeps rising out of the head until it is as far out as it can go.
Why tentacles come out of snail shells first
When a snail feels threatened, it quickly pulls its head and then its body into its shell for protection. A snail’s shell is actually back to front to make it possible for snails to do this – young snails permanently rotate their shell back to front so they can pull their head in before their body.
Getting their head hidden first gives snails the best chance of surviving an attack.
A backward shell puts a snail’s anus closer to its head than its tail, which is why snails often look like they’re pooping out the front of their body and not the back.
A snail stays in its shell until it thinks it’s safe to come out. But how can it check that the danger is gone?
The snail sticks out its tentacles and takes a look or smells to see if there is still danger nearby. If the predator manages to bite off a tentacle while the snail is checking for danger, the snail can grow another one.
If things look and smell safe, the snail’s body comes out of its shell. If it isn’t safe to come out, the snail stays in its shell for protection.
How to get rid of slugs and snails
If you want to get rid of slugs and snails in your yard, below are the best tips and recommended products from Amazon to get the job done:
- To make sure you have slugs or snails, look for them or look for the shiny, silvery mucus trails they leave behind.
- If you have slugs or snails in your yard, sprinkle these organic snail and slug killer granules to draw them out of hiding and kill them. The good things about these granules are they’re biodegradable, safe to use around pets, children, and wildlife, and are effective in all types of weather (even rain).
- If you have a problem with slugs or snails on certain plants or in certain areas, spray the plant or area with this non-toxic slug and snail repellent made with essential oils. This spray can be used indoors or outdoors, and even around the perimeter of your yard to keep slugs and snails out.
- In the evening, water your garden well and set a beer trap by putting a small plastic bowl in the ground near the plants the slugs or snails are eating. Put the bowl deep enough to leave 1 inch above the ground or cover the trap with a loose lid to stop insects from falling in. Fill the bowl halfway with fresh beer. Empty it out and put fresh beer in every night until you no longer find slugs or snails in the morning. If you don’t want to make your own beer trap, you can buy beer traps from Amazon.
- A DIY option is to go out and pick up slugs and snails with your hands (I suggest wearing gloves for this). The best time to look for slugs and snails is after sunset and rainfall. Throw the slugs or snails on the ground and stand on them or crush them with a rock. Or throw them into a bucket of soapy or salty water to drown them. Here are 10 things to do with all the snails you collect.
- If you have rose slugs, try making this dish soap spray and follow the instructions to kill the slugs with a direct spray of the soapy solution.