Do Insects Feel Pain? How Do They React to Potentially Harmful Stimuli?

Insects are largely considered to be mindless animals in the sense that they purely respond robotically- to impulses; however, new research bucks this trend with indications that these minute invertebrates indeed feel pain like other animals.

What Is Pain?

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. It is a personal subjective experience that includes negative emotions.

A distinction must be mentioned here between pain and nociception or the ability to respond to damaging stimuli. It is a sensory mechanism allowing animals to detect and avoid damaging stimuli.

The process called nociception detects unpleasant stimulations, sharp cutting, like chemical burning, or bruising pressure. The sensory nervous system holds an account of such kind of events which can induce a number of behavioral and physiological responses in animals.

Nociception is close to being a universal property of living beings. Even simpler microorganisms, such as bacteria, move away after the addition of a noxious stimulus like high pH. The reaction in nature is to shy away from any factor that has the potential hopefully to reduce damage or initiate a protective response.

On the other hand, chronic pain is a lingering kind of pain that continues after the originally hurt tissue gets healed. It could either be neuropathic or inflammatory pain. In human beings, there is the formation of chronic pain through either peripheral sensitization or central disinhibition.

To some extent, both nociception and pain can take place independently of each other.

Do Insects Feel Pain?

Most people tend to treat them indifferently because they are usually regarded as pests. They often experience various acts of violence, with people assuming that they do not feel anything and that they are incapable of feeling any level of pain.

The ability of an animal to detect probably damaging stimuli does not mean that their brain generates pain like those experienced by humans. However, there are prior studies that an insect has avoidant responses to potential damaging contact.

A 2019 experiment proved that fruit flies indicated chronic pain when their legs were removed. When an injury has completely healed, an insect's contralateral limb becomes hypersensitive.

Another study shows that just the opposite is true: bumblebees' response to heat really does depend on other motivations. For example, the authors of the research team offered bumblebees four feeders: two heated and two unheated. The feeders dispensed out sugar water, which is a primary reward that the bumble bees love.

Though all feeders contained sugar water in the same concentration, the insects reacted differently to the two that were heated. If the heated feeders provided sweeter sugar water, the bumblebees would then choose those.

It meant their love for sugar had subdued their hate for heat. It may indicate that bees do feel pain since, just like human beings, their responses are way more than simple reflexes.

It is the same framework that was used in this review to make an estimate of the evidence for pain in various insects and on the basis of which the UK government recently decided to award special protection to two larger invertebrate groups: the decapod crustaceans, such as prawns, lobsters, and crabs, and the cephalopods, which include squid and octopus.

It has eight criteria that an animal's nervous system can sustain the sensation of pain through brain-body communication. This also served as a basis for determining if a certain animal was taxed in the Animal Welfare Sentience Act 2022.

In the case of flies and cockroaches, six of these criteria fitted the bill, pointing to firm evidence of pain. Four were met by ants, wasps, and bees; three, by grasshoppers, crickets, moths, and butterflies.