For the first time, scientists have directly observed pain signals being transmitted 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 how we treat crustaceans – from seafood restaurants to research laboratories.
The study, published in the journal Biology, represents the first time scientists have used EEG-style measurements to record pain responses directly from a crab’s brain.
Shore crabs, those small greenish-brown crustaceans you might spot scuttling along beaches, were the focus of the investigation. The study examined whether these creatures possess 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 fire off signals saying, “Danger! Pull away!”
“We could see that the crab has some kind 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 crab’s soft tissues. The same happened when we applied external pressure to several of the crab’s body parts,” explains lead author Eleftherios Kasiouras, a PhD student at the University of Gothenburg, in a statement.
Unlike previous research that only observed how crustaceans behave when exposed to harmful stimuli, this study directly measured their neural responses – similar to how 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 the eyes, antennae, claws, and leg joints, applying either gentle 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 touched with 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 crabs can distinguish between different types of threats.
Particularly striking was the discovery that different body parts showed varying levels of sensitivity. The eyes and soft tissues between leg joints were incredibly responsive to touch, detecting pressure as light as 0.008 grams – about 75 times more sensitive than human skin. Meanwhile, their antennae and antennules appeared specialized for detecting chemical threats rather than physical pressure.
The antennae and antennules (smaller antenna-like structures) showed a fascinating specialization: they responded strongly to chemical stimuli but showed no response to mechanical pressure. This suggests these appendages may be specifically tuned to detect harmful chemicals in their environment, similar to how our nose can alert us to dangerous fumes.
“It is a given that all animals need some kind of pain system to cope by avoiding danger. I don’t think we need to test all species of crustaceans, as they have a similar structure and therefore similar nervous systems. We can assume that shrimps, crayfish and lobsters can also send external signals about painful stimuli to their brain which will process this information,” says Kasiouras.
The findings have significant implications for animal welfare practices. Currently, crustaceans aren’t protected under 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 notes, “We need to find less painful ways to kill shellfish if we are to continue eating them. Because now we have scientific evidence that they both experience and react 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 previously caused them harm. However, this is the first time scientists have directly observed the neural signals that drive these behaviors.
Previous studies relied mainly on observing how crustaceans reacted to various stimuli – including mechanical impacts, electric shocks, and acids applied to soft tissues like their antennae. While these crustaceans showed defensive behaviors like touching the affected areas or trying to avoid the threatening stimulus, scientists couldn’t definitively say these responses indicated pain sensation until now.
Whether this research will change how we treat crustaceans remains to be seen, but one thing’s clear: these sideways-walking creatures might deserve a second look – and perhaps a more humane perspective.