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Crab close up, Cuba
Crab close up, Cuba

How Could We Know If an Octopus or Lobster Felt Pain?

Researchers found that, when it comes to awareness, octopuses were the stars, followed by lobsters, crayfish, crabs, etc.

Some researchers, commissioned to find out, offered their wrap-up thoughts at Phys.org recently. They started applying the same standards to octopuses as are applied to mammals that are lab animals. Specifically, they used eight criteria for determining sentience — in the sense that, if you did the same thing to a dog and got the same reaction, would you assume it was pain? The results have been interesting:

We found the strongest evidence for sentience in cephalopods. Octopuses were the stars. With around 170 million brain cells, they have higher brain-to-body ratios than most reptiles and fish. This allows octopuses to perform remarkable feats of learning and memory.

Octopuses also behave in ways that point strongly to experiences of pain. For example, in a recent study, they were given three chambers to explore. Injection with acetic acid in their initially preferred chamber led to octopuses avoiding that chamber from then on. Injured octopuses learned to prefer an alternative chamber, where local anesthetic was available. This anesthetic silenced nerve activity between the injury site and the brain. Similar findings in mammals are taken to indicate the subjective experience of pain.

Alexandra Schnell, Andrew Crump, Jonathan Birch, The Conversation, “Octopus, crabs and lobsters feel pain: How we found out” at Phys.org (December 17, 2021)

That’s why the British government is now moving to protect octopuses from cruelty — as it would protect, say, pigs or cows.

Other experiments showed similar pain avoidance effects in lobsters, crabs, and crayfish:

Decapods also displayed compelling signs of sentience. For instance, one high-profile study allowed crayfish to explore a cross-shaped tank. Two arms of the cross were illuminated, whereas the other two were shaded. In the wild, crayfish use dark shelters to hide from predators, so time spent in the shaded arms was taken to measure anxiety-like behavior. Exposure to an electric field caused crayfish to avoid the light arms. Administering an anti-anxiety drug reversed the effect. These findings reveal that crayfish have mental states with similar brain mechanisms and behavior to anxiety.

Alexandra Schnell, Andrew Crump, Jonathan Birch, The Conversation, “Octopus, crabs and lobsters feel pain: How we found out” at Phys.org (December 17, 2021)

One outcome is that, in Switzerland, it is now illegal to boil lobsters alive without stunning them first.

If this all sounds preposterous, consider two things: Sentience (ability to feel pain) is assumed in mammals. So we reasonably believe that if dogs suffer pain, raccoons suffer too. But in fact, most vertebrates, never mind mammals, have not been studied with respect to pain.

Second, we have assumed that invertebrates were not “evolved” in such a way as to suffer pain (sentience). But some invertebrates turn out to be unusually intelligent and, no surprise, they are at the center of the pain controversy.

The researchers conclude:

We hope our report begins a wider conversation about how these animals can be treated humanely so we can minimize their pain and suffering. Many techniques, such as electrical stunning and rapid slaughter, are already informally considered best practice. Encouraging and enforcing best practice could protect producers against the erosion of standards, and reassure consumers that their expectations of high welfare standards are being met.

Alexandra Schnell, Andrew Crump, Jonathan Birch, The Conversation, “Octopus, crabs and lobsters feel pain: How we found out” at Phys.org (December 17, 2021)

The question of the origin and development of intelligence underlies the controversy, which has resulted in legislation.

There does not seem to be a “ladder of intelligence.” Octopuses, crabs, crayfish, and lobsters are apparently smart but nautiluses and other shellfish are apparently stupid. How does intelligence (and sentience) develop in one but not the other?

How exactly a life form acquires the ability to process large amounts of information and use it to make intelligent decisions (and perhaps end up feeling pain as an inevitable outcome) is a fruitful mystery for science to tackle. Some earlier assumptions might get blown up in the process.

You may also wish to read:

British government moves to protect octopuses from cruelty. The move to protect cephalopods and crabs/lobsters follows from research showing their intelligence and awareness of pain. Researchers are probing why some invertebrates are as smart as vertebrates. It seems that there is no straightforward evolutionary path to smartness.


Can crabs think? Can lobsters feel? What we know now How does a self that feels pain come to exist? And how do we distinguish information use — computer style — from self-awareness?

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How Could We Know If an Octopus or Lobster Felt Pain?