Find out the truth: do crabs feel pain?

GOTHENBURG, Sweden — For the first time, scientists have directly observed the transmission of pain signals to the brains of shore crabs, providing the strongest evidence yet that these creatures can sense and process pain. This discovery, made by researchers at the University of Gothenburg, could revolutionize the way we treat shellfish, from seafood restaurants to research laboratories.

The study, published in the journal Biologyrepresents the first time scientists have used EEG-like measurements to record pain responses directly from a crab’s brain.

Shore crabs, small greenish-brown crustaceans that can be seen scurrying along beaches, were the focus of the investigation. The study examined whether these creatures have what scientists call “nociceptors” – specialized sensory neurons that detect potentially harmful stimuli and send warning signals to the brain. Think of nociceptors as your body’s built-in alarm system: When you touch something too hot or sharp, these neurons quickly trigger signals saying, “Danger! Stay away!

“We were able to see that the crab has some sort of pain receptors in its soft tissues because we recorded an increase in brain activity when we applied a potentially painful chemical, a form of vinegar, to the soft tissues. “The same thing happened when we applied external pressure to several parts of the crab’s body,” explains lead author Eleftherios Kasiouras, a doctoral student at the University of Gothenburg, in a statement.

Unlike previous research that only observed the behavior of crustaceans when exposed to noxious stimuli, this study directly measured their neural responses – in the same way that doctors use an EEG to monitor human brain activity. The research team examined 20 shore crabs, focusing on how their nervous systems responded to both physical pressure and chemical irritants.

The research team used sophisticated equipment to record electrical activity in different parts of the crabs’ nervous systems. They tested various body parts, including eyes, antennae, claws and leg joints, by applying either light pressure with fine instruments or small amounts of acetic acid (similar to vinegar).

The results revealed fascinating differences in how crabs respond to different types of potentially harmful stimuli. When they were touched by pressure testing instruments, their nervous systems produced short, intense bursts of activity. However, when exposed to acetic acid, the response was more prolonged but less intense, suggesting that the crabs can distinguish between different types of threats.

Particularly striking was the finding that different parts of the body had different levels of sensitivity. The eyes and soft tissue between the leg joints were incredibly sensitive to touch, detecting pressure as light as 0.008 grams, about 75 times more sensitive than human skin. Meanwhile, their antennae and antennules seemed specialized in detecting chemical threats rather than physical pressure.

Antennae and antennules (smaller antennae-like structures) exhibited a fascinating specialization: They responded strongly to chemical stimuli but did not respond to mechanical pressure. This suggests that these appendages could be specifically tuned to detect harmful chemicals in their environment, in the same way that our noses can alert us to dangerous fumes.

“It stands to reason that all animals need some sort of pain system to cope with danger. I don’t think it’s necessary to test all species of crustaceans, as they have a similar structure and therefore a similar nervous system. We can assume that shrimp, crayfish and lobsters can also send external signals about painful stimuli to their brain, which will process this information,” explains Kasiouras.

The findings have significant implications for animal welfare practices. Currently, crustaceans are not protected by European Union animal welfare legislation, meaning they can legally be cut up while still alive – a practice that would be unthinkable with mammals. As researcher Lynne Sneddon points out: “We need to find less painful ways to kill shellfish if we want to continue eating them. Because we now have scientific proof that they both feel and respond to pain.

The study builds on previous research showing that crustaceans exhibit protective behaviors when injured, such as rubbing affected areas or avoiding situations that have previously caused them harm. However, this is the first time that scientists have directly observed the neural signals behind these behaviors.

Previous studies primarily relied on observing how crustaceans react to various stimuli, including mechanical impacts, electric shocks, and acids applied to soft tissues like their antennae. Although these crustaceans showed defensive behaviors, such as touching the affected areas or trying to avoid the threatening stimulus, scientists could not until now say with certainty that these responses indicated a sensation of pain.

Whether this research will change the way we treat shellfish remains to be seen, but one thing is clear: These side-moving creatures might deserve a second look – and perhaps a more humane perspective.