From being accidentally stepped on by careless walkers to being salted by frustrated gardeners or sautéed by chefs, snails face great risk to life and limb on a daily basis.
The question is, should one of these or any other unfortunate incidents befall the slow-moving gastropods, does it hurt them?
Yes, that’s right: what we’re asking today is do snails feel pain?
The quick answer is yes. A snail crushed underfoot will feel pain akin to how you would feel if stood on by a giant as tall as the Empire State Building. A snail that has been salted will feel pain similar to that you’d feel if doused in acid. The extreme suffering you’d experience if thrown into a vat of boiling oil? That’s the pain a snail feels when thrown into a frying pan with some garlic.
However, if you have a few minutes, read on for the considered answer and learn why we’ve drawn that conclusion and what others think.
Are you still with us? Great: let’s start with some definitions and get into our discussion.
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What are snails?
Snails are a type of gastropod (a word derived from the Greek words for ‘stomach’ and ‘foot’ because of those two parts of their body being in such close proximity) with a coiled shell large enough for them to retreat inside when the need arises. Those we tend to be most familiar with are land snails, but there are also sea snails, sea slugs (which somewhat confusingly, are another type of snail), and finally slugs – a type of snail without a shell.
What is pain?
Although almost all of us are familiar with the sensation of pain, this is in fact quite a difficult question to answer.
Although there are a huge variety of definitions of pain, the two essential features we can focus on are nociception (the capacity to detect a stimulus that can potentially cause damage) and sentience (the sensation of suffering felt when nerve endings have been stimulated).
Nociception induces a reflex response in which the animal moves away from the cause of damage. It is possible for this to occur without any consequent suffering – in the case of unicellular organisms or bacteria, for example. The reason for this is they lack a nervous system.
So, when one of those creatures shifts to avoid the cause of bodily damage, they do it purely out of reflex, not choice. It’s similar to what happens when we sneeze – we don’t choose to do it.
However, the animal that feels pain makes a choice about how it is going to reduce, remove or prevent it and as such is capable of taking different measures according to circumstances. Unlike the aforementioned unicellular organisms and bacteria, these animals have a nervous system, meaning signals are sent from nerves to the brain. Snails are among the animals in possession of a nervous system.
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How do we know snails feel pain?
Not everybody believes they do. We are nothing if not objective, so we will always present reasonably argued perspectives that differ from our own. Those who argue that snails (and many other animals) do not feel pain base their conclusion on the basis that those animals do not:
- live for a long time
- have sufficient cognitive capacity
- experience emotion
That is a perspective, but we respectfully disagree. The evidence strongly suggests that none of those factors are necessary conditions for an animal to feel the uncomfortable sensation we know as pain.
Cognitive capacity is not a pre-requisite for feeling pain. Not only do humans with lower cognitive abilities feel pain just as intensely as those with greater ones, but the same is true of species whose mental abilities fall far short of our own.
As to how painful an experience is, we cannot know precisely how painful any injury is to another individual, people included. It is entirely subjective. The pain you feel when dropping a book on your finger may well differ from that of another person, even one who is very similar to you in size, age and resistance to pain.
We can only form an approximation of how painful that experience is because we cannot feel it ourselves. However, we are able to assess approximately how uncomfortable it is by communicating with that other person. Information gained through making more than one such comparison means we are even able to gain an idea how painful an experience we have never had may be.
Now, that’s all very well and good with other people. The obvious drawback with non-humans is the language barrier: they are not able to tell us anything so precisely about their discomfort. However, they are able to tell us in other ways. In some circumstances it will be through howling or squealing in pain, in other cases it will be demonstrated by the speed and extent to which they remove themselves from the cause of injury.
It is clear that a snail does not give us an audible clue when it feels pain. However, it gives us behavioral signals that mimic those of supposedly ‘higher’ animals and even humans. Snails exposed to high temperatures do all they can to escape the pain and learn to take an indirect route rather than their previously preferred one to reach a target.
In addition, snails, along with several other invertebrate species, alter their behavior to avoid electric shock in exactly the way vertebrates, including humans, do in similar circumstances.
These examples are the ones that prove the snail is experiencing pain rather than just a reflex – their avoidance techniques vary. It is that variation that shows they are making a choice about the way they respond to the cause of damage and that in turn reveals they are experiencing discomfort and not only detecting they have been damaged in some way.
So, taking everything into account, it is our considered opinion that snails do indeed feel physical pain.
Yes, it is questionable whether they can feel the emotional pain such as loss that humans and several other animals with well-developed cognitive abilities can sense, but the weight of evidence strongly suggests they feel physical pain on a similar continuum to us: the worse the damage, the greater the pain.
Minor damage causes less pain, greater damage causes more pain.
On the other hand, when a snail isn’t able to find lettuce to eat it doesn’t feel the sadness you feel when you can’t get hold of your favorite pizza or burger!