Switzerland’s animal welfare legislation recognizes the sentience of invertebrates, including cephalopod molluscs and decapod crustaceans. These include, for example, marine animals such as octopus and squid and crabs and lobsters. This decision was based on evidence that emotions and felt experiences (i.e. sentience) are not limited to humans and animals that are genetically closer to humans, such as mammals. This debate was initiated nearly a decade ago when it was questioned whether fish could feel pain.
But pain is not emotion. Pain, known as nociception, is the unconscious reaction to harmful stimuli. This reaction is relayed by the peripheral nervous system1 and does not require the brain for the initial response. In contrast, emotion requires a subjective experience that can be either appealing or aversive, positive or negative. For instance, when it was found that fish could learn from negative experiences, and avoid dangerous situations, it was therefore concluded that fish had “felt” and processed these harmful situations.
When it comes to insects, it has long been thought that they would respond to harmful stimuli repeatedly, without learning. In a study published in PNAS, Matilda Gibbons and her colleagues challenged this paradigm by presenting bumblebees with a solution with various concentrations of sugar (from 10 to 40%) — with the highest sugar concentration being the bees’ preferred option. However, when the 40% feeder was heated to 55°C, the bumblebees traded off their motivation to avoid uncomfortable heat against their preference for the high levels of sugar. When the unheated feeders had a lot of sugar, the bees avoided the hot feeders. But when the unheated feeders had less sugar, the bees were more willing to go to the hot feeders for the sweeter reward. This means that the bees made a decision based on their motivation: they were willing to put up with the heat if the sugar was worth it. The bees made these choices by learning to recognize colors that were associated with different sugar levels, suggesting that they were using their brains to weigh the options and decide, rather than just reacting automatically. This behavioral response demonstrated the involvement of the central nervous system2 (which involves the brain) to avoid heated feeders, which supports the idea that even insects can experience a form of sentience.
As research continues to shed light on the complexities of insect behavior, the question of whether insects experience emotions remains open but increasingly compelling. If even creatures as small as bumblebees demonstrate decision-making that reflects a form of sentience, it challenges us to rethink our assumptions about the boundaries of emotion and experience in the animal kingdom. This evolving understanding may have profound implications for how we treat all sentient beings, regardless of size or complexity, and pushes us to consider a more inclusive view of empathy and ethical responsibility.
1 The peripheral nervous system (PNS) consists of nerves that branch out from the brain and spinal cord, reaching every part of the body. These nerves carry messages back and forth, telling the body what to do and bring information from the senses back to the brain.
2 The central nervous system (CNS) includes the brain and spinal cord and regulates the body. The brain processes information and makes decisions, while the spinal cord sends signals between the brain and the rest of the body. The CNS is the main control center, and the PNS is the network that connects this control center to the entire body, allowing us to move, feel, and respond to our surrounding.
Authors: Christopher Cederroth, Jessica Lampe & Robbie I’Anson Price, Swiss 3R Competence Centre
References:
De Waal & Andrews K (2022) The Question of Animal Emotion. Science. 375:6587. https://doi.org/10.1126/science.abo2378
Gibbons M, Versace E, Crump A, Baran B, and Chittka L. (2022) Motivational trade-offs and modulation of nociception in bumblebees. PNAS 119(31):e2205821119.
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