(ORDO NEWS) — We have long considered insects to be instinctive, mindless creatures with robotic responses to the world and all of its impulses.
But the closer we look, the more amazingly complex behaviors we discover, from bees communicating through dance to incredible feats of ant cooperation, and now we have more and more evidence that these little creatures that rule our world can also experience pain.
Nociception – the sensory nervous system’s detection of unpleasant stimulation, including chemical burning, a sharp cut, and pressure on a bruise – elicits a variety of physiological and behavioral responses in animals. One of them may be the perception of pain.
Insects have been documented to exhibit an avoidance response to potentially damaging contact.
What’s more, in 2019, experiments showed that a widely studied fruit fly, Drosophila, developed symptoms of chronic pain after researchers removed its leg.
After the fruit fly completely healed, the researchers found that the opposite leg of the fruit fly became hypersensitive.
The authors observed that the fly had lost the “pain brake” mechanism in the nerve cord. The mechanism of pain inhibition softens the perception of pain, but in fruit flies, when the sensory nerves were overexcited, it completely destroyed the inhibitor.
But since even bacteria will evade unpleasant stimuli, detecting pain in another life is not as easy as observing a negative reaction to a harmful contact. To consciously register the sensation of pain requires a complex physiological system connected to our brain, and perhaps even emotions.
In mammals, nociceptors (pain receptors) send an alarm signal about unpleasant stimuli to our brain, where neurons generate a negative and subjective, physical and emotional sensation of pain.
Research shows that nociception and pain can be independently regulated and have identified separate systems for regulating each.
These systems have not yet been fully identified in insects.
“One of the hallmarks of human perception of pain is that it can be modulated by neural signals from the brain,” Queen Mary University neuroscientist Matilda Gibbons told Newsweek.
“Soldiers sometimes don’t notice serious injuries on the battlefield because the body’s own opiates suppress the nociceptive signal. So we wondered if the insect brain contains the neural mechanisms that make it possible to perceive pain, rather than just basic nociception.”
Gibbons and colleagues reviewed the scientific literature and found some evidence that this mechanism is present in insects.
Although they lack the opioid receptor genes that suppress pain in us, during traumatic events they produce other proteins that can serve the same purpose.
Behavioral evidence also suggests that insects have molecular pathways that inhibit the response to damaging contact in both the peripheral and central nervous systems. For example, the presence of a sugar solution inhibits bumblebees’ normal avoidance of unpleasant stimuli.
Anatomically, insects have neurons descending from the brain to that part of the nerve cord from which their defensive response against injurious touch originates.
What’s more, the tobacco hornworm even uses behaviors to mitigate the effects of injury, such as grooming.
Each of these signs individually may not be conclusive, but taken together, they indicate that insects do indeed have some kind of pain control system similar to ours.
“We argue that insects most likely have central neural control over nociception based on behavioral, molecular and anatomical neuroscience data,” the team concludes in their statement. “Such control is consistent with the existence of pain experience.”
Because insects are a large and diverse group, it is possible that the sophistication of nociception regulation and potential pain sensations also vary widely.
The prospect of their pain, however, raises important ethical questions for further study – especially in light of the prospective mass breeding of these animals in the future.
“We are at a major crossroads on how to feed a human population projected to reach 10 billion by 2050,” the researchers said.
“While conventional animal husbandry is a major contributor to climate change, the United Nations recommends that insects be mass-produced for food. However, the ethical implications have not been carefully considered, as protection of animal welfare generally does not extend to insects.”
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