We swat bees to avoid painful stings, but do they feel the pain we inflict? A new study suggests they do, a possible clue that they and other insects have sentience—the ability to be aware of their feelings.
“It’s an impressive piece of work” with important implications, says Jonathan Birch, a philosopher and expert on animal sentience at the London School of Economics who was not involved with the paper. If the study holds up, he says, “the world contains far more sentient beings than we ever realized.”
Previous research has shown honey bees and bumble bees are intelligent, innovative, creatures. They understand the concept of zero, can do simple math, and distinguish among human faces (and probably bee faces, too). They’re usually optimistic when successfully foraging, but can become depressed if momentarily trapped by a predatory spider. Even when a bee escapes a spider, “her demeanor changes; for days after, she’s scared of every flower,” says Lars Chittka, a cognitive scientist at Queen Mary University of London whose lab carried out that study as well as the new research. “They were experiencing an emotional state.”
To find out whether these emotions include pain, Chittka and colleagues looked at one of the criteria commonly used for defining pain in animals: “motivational trade-offs.” People will endure the pain of a dentist’s drill for the longer term benefits of healthy teeth, for example. Similarly, hermit crabs will leave preferred shells to escape an electric shock only when given a particularly high jolt—an experiment that demonstrated crabs can tell the difference between weak and strong painful stimuli, and decide how much pain is worth enduring. That suggests crabs do feel pain and don’t simply respond reflexively to an unpleasant stimulus. Partly as a result of that study, crabs (and other crustaceans, including lobsters and crayfish) are recognized as sentient under U.K. law.
Chittka’s team gave 41 bumble bees (Bombus terrestris) a choice between two high-quality feeders containing a 40% sugar solution and two feeders with lower percentages of sucrose. The researchers placed the feeders in a testing arena on top of individual heating pads colored pink or yellow. Initially, all the heating pads were turned off; the bees entered the arena one at a time and sampled the feeders. They had to sip from each one to detect the amount of sugar. All preferred the feeders with the most sugar.
The scientists then warmed up the yellow pads beneath two of the high sucrose feeders to 55°C (temperatures above 44°C can be fatal to insects); feeders on the pink pads stayed cool. For a bee, landing on a hot yellow pad would be like us “touching a hot plate,” says lead author Matilda Rose Gibbons, a behavioral neuroscientist and Ph.D. student in Chittka’s lab. But bees that could withstand the pain would also get more sugar.
When given a choice between hot, sugar-rich feeders and cool, low-sugar feeders, the bees chose the former, the scientists report today in the Proceedings of the National Academy of Sciences. “If the sugar was superconcentrated, the bees would put up with more pain,” Gibbons says. “They could walk away whenever they wanted, but they didn’t. Getting that sugar was a huge motivator.” When both the hot and cool feeders held high-sugar solutions, the bees avoided those on the yellow pads—demonstrating they used associative memories when choosing where to feed, the scientists report.
Besides crustaceans, “This is the first direct demonstration that arthropods”—a group that also includes insects and spiders—“can also do trade-offs,” Birch says. He calls the study “intellectually fascinating” and “ethically important,” given growing interest in farming insects for human consumption—and the complete lack of “research into the welfare needs of insects.”
Still, it remains unclear whether bees really feel what we call pain; the scientists point out that their study does not provide “formal proof” of this ability. Given its subjective nature, “proving that insects feel pain is probably impossible,” says Greg Neely, a behavioral geneticist at the University of Sydney. He has shown fruit flies’ nervous systems can experience chronic pain, but he doubts that insects have the neurological systems to allow pain to register as a complex emotion.
Definitively proving insects mentally feel pain probably isn’t possible, agrees Jennifer Mather, a zoologist and cephalopod expert at the University of Lethbridge whose studies helped prove those animals are sentient. Nevertheless, given that insects represent at least 60% of all animals, she says, “We can’t ignore them. There is still anthropocentrism in Western science that rejects the idea of caring about ‘dumb invertebrates.’ Papers like this one will gradually chip away at this self-centered attitude.”