Robert Elwood once boiled a lobster alive – lobsters being one of the few creatures we eat that we are allowed to slaughter at home. It is the usual way to kill, and cook, them. “Would I boil a lobster now?” asks Elwood, emeritus professor at the school of biological sciences at Queen’s University Belfast, referring to the work he has done for more than a decade on crustaceans and pain. “I wouldn’t. I would kill it before boiling.”

The question of whether lobsters feel pain – and the way people should (or should not) treat them – has been raised again recently. Last week, a London-based company had to defend the sale through Amazon of live lobsters, which are confined in packaging and posted to consumers. Other fishmongers in the UK, not on Amazon, also courier live lobsters to people at home. Last month, Switzerland banned the practice of boiling lobsters alive, which is already illegal in New Zealand. From 1 March, as part of an overhaul of animal protection legislation, the animals must be stunned electrically before cooking.

It is unthinkable that we would be sold a live chicken or lamb to kill at home. Why do some people think of lobsters differently? “They look so different to us, they dwell in completely different environments to us,” says Maisie Tomlinson, campaign director of Crustacean Compassion, which lobbies for the humane treatment of crustaceans. “With their hard shells and peculiar appearance, it can seem that perhaps they don’t feel pain; they look quite tough. But I think that, more and more, people are recognising that it’s not how an animal looks, it’s the scientific evidence of their sentience.” It is time, says the campaign group, to change our attitude to lobsters and other decapod crustaceans, such as crabs, that are treated in a similar way – limbs pulled off, often sold live, sometimes boiled alive.

The organisation was set up in response to a story in the news in 2015 about a Korean supermarket in Surrey that sold live crabs, packaged in clingfilm, for home slaughter. “We discovered that, although the RSPCA were able to have a word, they weren’t able to take further action, because these creatures weren’t protected under the Animal Welfare Act 2006,” says Tomlinson. “When we looked into the science and found how much research there has been into decapod pain, we were really shocked.”

‘The highest population density of lobsters in the world is off the coast of Maine’ ... a US fisherman shows off part of his catch. Photograph: Daniel Grill/Tetra Images/Getty Images

Crustacean Compassion is lobbying the government, which is looking at animal welfare legislation, to include decapod crustaceans in its definition of “animal”. “At the moment, the Animal Welfare Act only covers vertebrates,” says Tomlinson. “There is, however, a clause that allows for the inclusion of any invertebrates if the government is satisfied that the animals are capable of experiencing pain or suffering. We discovered [through a Freedom of Information request] that the government had conducted no assessments of the sentience of decapod crustaceans since at least the time of the 2005 animal welfare bill. We’re arguing that now the evidence is there that shows it is highly likely [that crustaceans are] capable of experiencing pain.”

So, should we all be campaigning on this issue? Much of the research on which Crustacean Compassion bases its campaign comes from Elwood. “There is tremendous difficulty in asking questions about animal pain, because there’s no definitive experiment that will say: now I’ve proved it,” he says. “That applies to all animals. We’re very accepting that cats and dogs experience pain – I think it would be the unusual person who said they didn’t, categorically – but it’s only done on probability. There’s no absolute proof.”

The usual argument against them feeling pain is that their brain structure is so different to ours. “The argument is: we know the areas involved in pain experienced in humans; if you don’t have those areas, you can’t feel pain. But it’s quite clear that, in evolution, completely different structures have arisen to have exactly the same function – crustaceans don’t have a visual cortex anything like that of a human, but they can see. Given the evolutionary advantage of experiencing pain, there is no reason to assume they should not have this protection against tissue damage.”

There is as much evidence for pain in crustaceans as there is in many vertebrates Prof Robert Elwood

The accepted wisdom about crustacean behaviour in response to stimuli was that it was a reflex, not a reaction to pain. “Again and again, we found that these animals were responding outside a reflex,” says Elwood. “For example, the first experiment we did was to put a weak acid on to one antenna of a prawn. The animals then engaged in prolonged rubbing and scraping of that specific antenna. If you wound a crab, they guard it – they put their claw over the wound – if another crab is nearby. These things are consistent with the idea of pain.”

Elwood and his team looked at what he calls “motivational trade-offs”. They delivered small electric shocks to hermit crabs, who live in empty snail shells. Some of the crabs left their shell, although they were more likely to leave if their shell was from an unpreferred species – they appeared to feel they had less to lose.

He also showed they could remember “pain”: if, after receiving an electric shock, they did not leave their shell, they were much keener to swap their shell for a different one 24 hours later than a crab who had not received an electric shock. “Their whole motivation about their shell has been changed by a small electric shock,” says Elwood. In another experiment, shore crabs learned to avoid a location in which they had received an electric shock. “We also found that there were stress hormones being produced after an electric shock.”

Is he convinced crustaceans can feel pain? “We’re now in the area where you can say there is as much evidence for pain in crustaceans as there is in many vertebrates,” he says. “Vertebrates generally receive some sort of welfare protection; crustaceans don’t.”

Live lobsters for sale on Amazon. Photograph: Amazon

Other scientists are less sure. “I’m not convinced they feel pain,” says Robert Steneck, professor of marine sciences at the University of Maine. “There is no compelling case I’ve seen that suggests they feel pain. You don’t really see this level of concern for people who eat oysters or clams – they’re certainly every bit as alive. The problem has more to do with how we anthropomorphise various critters. The fact that lobsters move and clams don’t, that they have eyes – I think that it does tend to increase our sensitivity to their end of life more than having a raw oyster.”

Steneck has been studying lobsters since 1983 in the waters around Maine, the north-eastern-most US state. It is home to 1.2 million people and 3.5m lobster traps. Maine – and the coastline north of it, in Canada – is the sweet spot for lobsters, he says, thanks to its cool water. “The highest population density of lobsters in the world is off the coast of Maine,” he says – and they catch a lot of them. What is surprising, says Steneck, is how sustainable the practice appears to be. “All the accounts show the stock is increasing in abundance and, if you look at the catch of lobsters per trap, it continues to go up,” he says. “That’s been increasing, despite the pressure on them. It’s the only fishery I know of that has been targeted for almost 200 years and is doing better today than ever before.” (There is one sustainable lobster fishery certified by the Marine Stewardship Council in the British Isles – the cross-border Jersey Normandy fishery, made up of about 130 small fishing boats.)

Overfishing of other species has helped Maine’s lobster boom. Steneck says it has “domesticated our ecosystem. By that, I mean we’ve removed all the predators – we used to have cod, hake, haddock, active predators in coastal Maine. They’ve all gone, they’re overfished.” Smaller, younger lobsters can escape from lobster pots, having eaten the bait that was supposed to help entrap them. “Every lobster trap, every two days, gets a kilo of bait. We’re feeding them.” The lobsters’ nursery habitats, where larvae develop, are mostly empty of other species, “but they’re loaded with other crab in Europe, [which] probably contributes to the very low density of European lobsters you have”.

Maine’s lobstermen have a high conservation ethic, he says. For instance, they put a notch in the tail of breeding females “so nobody can harvest them. There is a minimum legal size, but there is also a maximum legal size, above which you can’t harvest the lobsters and they could live for another 50 years.”

Lobsters are fascinating creatures. They are solitary, except when mating – they probably would not appreciate being kept in a tank with other lobsters – and they can live to 100. When they grow out of their carapace, it splits and the creatures backs out of it, vulnerable and naked, until it grows a new one. “Everything that is what we’d call ‘skin’ moults,” he says. “It’s not just their skin – it includes their oesophagus. Then they have a kind of papery skeleton.” Touch one of these before it becomes hard and you will kill it instantly. “Unfortunately, I’ve come across this on a few occasions, where I’ve grabbed it to measure it,” says Steneck.

According to Prof Robert Steneck, ‘there is no compelling case I’ve seen that suggests lobsters feel pain’. Photograph: Beverly Factor/Getty Images

Females also moult to mate; in his book The Secret Life of Lobsters, Trevor Corson describes it as “undressing”. “The male sometimes guards the female as she hardens up, because she’s very vulnerable,” says Steneck. “The mating system is a little bit like wolves, in that there are dominant males that compete with other males, and females compete with each other for the best shelters. You can have one dominant male fertilise 10 females and the females will delay their shedding until they have access to this stud.”

Such is the life of a lobster – unless it ends up being caught, bound and sent to a restaurant or the home of an overambitious cook who then wonders whether they can go through with the slaughter. “It’s estimated that an edible crab that is boiled alive may take up to three minutes to lose consciousness,” says Tomlinson. “That’s something that would be unconscionable in a vertebrate animal, where they talk about milliseconds to lose consciousness [in a slaughterhouse].”

Some restaurants stun their lobsters before cooking. A spokesperson for the restaurant chain Burger & Lobster, a significant importer of live lobsters, says it has “adopted a humane dispatch method ... using a pressurised environment with high-velocity steam [that] cannot be compared with boiling a lobster alive”. The system is the result of years of research, the spokesperson says, but the research has not been published and the spokesperson could not or would not say by whom it was conducted, other than “a collection of our chefs, marine biologists and lobster fishermen”.

Is there a best way to kill a lobster? “I know some people like to put them in the freezer [before cooking them in boiling water],” says Steneck. “I’m not sure that’s a great way to go.” Elwood says that, if he were running a restaurant, “I would have [a device] that gave them electrical stunning, which completely destroys the central nervous system in a microsecond”. At home, as a biologist familiar with lobster anatomy, he would know where to stick a knife in at the back of one’s head before splitting it in two, destroying the brain and the nervous system. “That should take someone a second if they know what they’re doing,” he says. The average person “might end up doing more harm than good, by stabbing the animal in various places before it’s killed”. Putting ethics aside for a moment, there is nothing like a bit of inept murderousness to put you off your dinner.

• This article was amended on 13 February 2018. An earlier version referred to the UK in a mention of the Jersey Normandy fishery; the crown dependency of Jersey is not part of the UK but is in the British Isles.