Science Questions

Can slugs and snails feel pain?

Sun, 17th Jun 2012

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Question

Karen Wells asked:

Chris

 

I'd like to know if slugs and snails feel pain?

 

They are the bane of my horticultural life and I would like to know which is the most humane way of dispatching them, apart from natural predators?

 

K x

 

 

Answer

I wasnít actually sure about the answer to this to start with, whether things like slugs and snails do actually feel pain.  The way that the medicines and the drugs work that you put into slug pellets is they basically just cause them to expire through various toxic ways which are not going to affect humans and other animals and mammals.  You're exploiting a chemical problem that the snail has when it eats this stuff compared with us.

Then I looked back at a story I wrote about 5 years ago - "Can prawns feel pain?"  Bob Elwood, at Queens University Belfast, published a paper showing that prawns, when he dabbed a vinegar onto their pincers and on their antennae, seem to flinch, and he suggested this was because they felt pain.  Then I found that heís actually published a follow up paper and I've looked that up for you.  I'm actually quoting from Science Daily, but it says here:

ďNew research published by Queens University Belfast Academic has shown that crabs don't just suffer pain, but they also remember it too.  The study looked at the reactions of hermit crabs to small electric shocks and it was carried out by Professor Bob Elwood at the School of Biological Sciences at Queens University Belfast, and published in Animal Behaviour.  Professor Elwood, who has previously carried out a study showing that prawns endure pain, said that his research highlighted the need to investigate how crustaceans used in food industries are treated."

Obviously, this is about crabs and you're asking about slugs and snails, but they are closely related in the grand scheme of things, and therefore, itís reasonable that if we read what happens to a crab, we can sort of extrapolate to a snail. 

Now he goes on to say, wires were attached to the shells of the hermit crabs to deliver small shocks to the abdomens of some of the crabs in their shells.  The crabs that got out of their shells were those that had received shocks, indicating the experiment was unpleasant for them and it shows that central neuronal processing, in other words, they realise it was unpleasant the they decided to vacate their shell.  It wasnít just a reflex response. 

He also says that crabs that have been shocked that had remained in their shell were appeared to remember the experiment of the shock because they quickly move towards a new shell when they were offered one, compared with the shell they were already in.  In other words, they prefer certain shells over others and if they're in one that they're already been uncomfortable with and you then shock them, they're much more likely to vacate the premises and go for a new shell. 

So, this would suggest that simple creatures like prawns and also crabs, and hermit crabs can experience pain. 

Therefore, I think itís probably not unlikely that if you bring a snail to an untimely end by pouring salt over it or poison it with some slug pellets, itís probably not very pleasant for the slug or the snail.

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I think that snails must feel pain. As a child, I poked snails in the eye, and they withdraw their eye-stalks to protect their eyes. It's like the human reflex when we get a poke in the eye. evan_au, Wed, 20th Jun 2012



Sorry Doc, but I must take issue with you on this point.



See the whole post here:- http://www.thenakedscientists.com/forum/index.php?topic=44496.msg390642#quickreply

Used properly, slug pellets should not be a problem, but the trouble is they are all too often used incorrectly, with far too much being put down at a time.

The doses required to kill slugs falls well short of the doses required to have any effect on other animals. However, Angela Squires, who runs a Hedgehog hospital, claims to be finding poisoned hedgehogs. See this. And in 2009, the Daily Mail reported this case of dog poisoning. Amazing, maybe, but horses have also died from low doses of metaldehyde. NCBI

You might also read this entry in the Merck Veterinary Manual and this from the Cornell University.

Our tortoises have free range in our garden, so we do not use slug pellets. Having tried other remedies with only limited success, we turned to nematoads and so far with 100% success.

I think slug pellets need more investigation into their affect on other animals and what concentrations might prove dangerous. Although the active ingredients of slug pellets are said to neutralise on ingestion by slugs and snails, I wonder if this might not be the case where large quantities have been ingested, or if the dead slug can be described as 'safe' when ingested by another animal. Don_1, Wed, 20th Jun 2012

I've checked my "child-friendly" slug pellets, which tell me that they don't contain the stuff listed above but are instead based on aluminium sulphate - so they won't kill me, but they could give me Alzheimer's if I eat the whole tub. Now I'm wondering if slugs can get Alzheimer's too... chris, Thu, 21st Jun 2012

I'm sorry, but you CANNOT compare snails and crustaceans like that. That is like comparing apples and carrots. It is not right to extrapolate the results of what happens to crabs to what happens to snails, as they are in almost no way related. Crustaceans are arthropods, while snails are molluscs. Besides, insects and crabs are both arthropods, but it has been proven that most insects (with the exception of the fruit fly) do not experience pain. The same for oysters. Snails, oysters and slugs are all molluscs, yet oysters have no central nervous system. However, I have read some reports that nociceptors have been found in the gastropods Aplysia (a sea slug) and Helix (garden snails) have nociceptors and are capable of operant conditioning, so pain is not out of the question for these two gastropod groups. So if you have to kill them, do it quickly to avoid any potential pain. Anonymous, Mon, 7th Oct 2013

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