Do insects feel pain?

To answer this question, first we must look at what we are asking: what do we mean by “feel”? and what is “pain”?

When discussing the subject of pain, researchers make the distinction between nociception – “the sensory nervous systems response to harmful or potentially harmful stimuli” [1], and pain – the subjective experience of anguish, suffering, or other negative affective states.

It is becoming clear then, that the question of pain in insects (or any other organism for that matter) actually refers to the question of whether or not an insect can have a subjective, emotional state, which is a much harder question to answer.

maurice3
This is Maurice the wasp (possibly, Vespula germanica? I’m not sure, is there an entomologist in the house?!) who decided to hang around my windowsill after a cold night. Doesn’t it look cute with its little puppy-wasp face? If you pinch it, will it not get pinched??

Let’s first consider the necessary conditions for the perception of pain.

“The neural apparatus”

Researchers agree that a necessary condition for the perception of pain is the existence of nociceptors – neurons dedicated to sensing damaging stimuli.

In humans, the process of nociception occurs when nociceptors – sensory nerve cells connected in pathways to the spinal cord and brain, are activated by different types of noxious stimuli. Nociceptors are distributed all around and inside the body. The first thing to consider when asking whether or not a certain organism is capable of experiencing pain, is whether or not that organism possesses the proper “equipment” to perceive and process noxious input.

Nociception does exist in insects, although little is known about how nociceptive information is processed within the insect.

Another dimension to consider is the responses to nociception – physiological and behavioral.

How do insects behave when they sense pain?

The research on the concept of pain started out very human-centric. Because humans are the only animal which can verbally communicate and report their internal state (feelings, emotions, sensations, drives, motivations, etc.), and thus produce rich measures for research, when researchers examine pain in other animals, they were looking for human-like behaviors in response to pain, and for analogous-to-human brain and CNS circuitry and mechanisms in these animals. When we get a cut on our hand, we immediately withdraw it, or rub it. If humans are severely injured, they will usually stop what they’re doing to address the injury. That is not the case with insects however.

In a first report on insect pain from 1984, Eisemann and colleagues[2]  described how insects do not display common behavioral responses to pain. For example, an insect will not limp after removal or injury to a limb, and some species might continue to mate or feed even after or during serious injuries or dismemberment. The sexual cannibalism behavior in species of Mantis comes to mind as an obvious example. While mating, the female mantis might start to feed on the male (starting with the head, which is possibly both convenient and delicious), but the male will continue to mate with her, moving even more vigorously in its delivery of sperm.

Eisenmann concluded that while this evidence does not prove that insects do not feel pain, if insects do have a sense of pain, ‘it does not have any adaptive influence on behavior’.

The behavioral responses to pain – from simple to complex – criteria for pain perception

The behaviors described above seem to point to the conclusion that insects do not possess the subjective experience of pain, despite the fact they do possess nociception.

However, since the 80’s further investigations revealed more complex responses to pain in insects. Insects respond to noxious stimuli, they may change their behavior when faced with damaging stimuli, and can even be trained to perform various tasks using noxious stimuli, suggesting a motivational shift in response to pain or perceived threat of injury.

Sneddon and colleagues[3] suggested to evaluate the potential for pain in various species, including insects and other invertebrates, on two planes: First, the responses to a noxious event should effect the animal on the physiological, neurobiological, and behavioral level, and this response should be different from the response to a harmless stimulus, and this behavior should change including avoidance learning and protective behavior. This plane of evaluation includes the existence of nociception. The second plane of evaluation will include a long-term motivational and behavioral change after a painful event: self-administration of analgesia, paying a cost to access analgesia or avoidance of painful stimuli and reduced performance in concurrent events. In this view, insects fail to fulfill most of the criteria from the second plane, while the behavioral changes that they do display, can be explained using nociception alone. One might say then that insects are more like robots than mammals.

However, it is possible that insects possess certain aspects of an emotional experience, but lack others. If insects indeed do not feel pain per se, then what can explain their complex behaviors? The answer might come from robots [4].

What can robots teach us about pain?

But does a behavioral response to nociception necessarily point to a subjective experience of pain?

Current advances in AI exemplify the notion that a subjective emotional experience is not necessary to produce complex motivated behavior.

One example is this (rather creepy) “dental patient” human-like robot designed to mimic human responses to pain, and used for training for dentist procedures. These robots will flinch, cry, and show mimics of human pain responses in response to careless treatment by the dental student.

An AI can also be programmed to have motivation to move when sensing discomfort, changing its behavior flexibly to avoid threat or get away from it, like the virtual system MoNETA[5], which is basically a virtual rat, programmed to learn how to navigate a Morris Water Maze. Its underlying subscripts are programmed so it will try to avoid “discomfort” and approach pleasant stimuli.

These examples demonstrate that an artificial entity with a nociceptive-like system, can respond to unpleasant events and stimuli in a similar way to natural entities, even without the existence of “feelings” per se. One might use this example to argue that, just like robots, insects too have simple systems who generate complex responses for damaging events without the subjective experience of pain.

However, the flaw in this argument is that the behaviors of robots are intelligently designed, while insects are naturally selected, so their behavior must have some sort of evolutionary benefit.

Are insects conscious?

Recently, Klein & Barron[6] (a philosopher and a neurobiologist), recognized structures in the insect brain that are functionally analogous to the integrated structures in the vertebrate brain which support the capacity for consciousness. Klein & Barron thus argue that insects may also have a capacity for subjective experience, feelings, and consciousness.

The debate over the question of pain in insects is multi-dimensional in that it encompasses theories, evidence and opinions from philosophers, biologists, neurobiologists and more. The question of ‘pain’ is “nested” within the bigger question of consciousness and subjective experience. and as such, it might take a long time to answer.

References:

  1. (2016, September 12). In Wikipedia, The Free Encyclopedia. Retrieved 16:09, September 30, 2016, from https://en.wikipedia.org/w/index.php?title=Nociception&oldid=739087092
  2. Eisemann, C. H., Jorgensen, W. K., Merritt, D. J., Rice, M. J., Cribb, B. W., Webb, P. D., et al. (1984). Do insects feel pain? A biological view. Experientia, 40.
  3. Sneddon, L. U., Elwood, R. W., Adamo, S. A., & Leach, M. C. (2014). Defining and assessing animal pain. Animal Behaviour, 97.
  4. Adamo, S.A. (2016) Do insects feel pain? A question at the intersection of animal behaviour, philosophy and robotics. Animal Behaviour, 118.
  5. Ames, H., Mingolla, E., Sohail, A., Chandler, B., Gorchetchnikov, A., Leveille, J., et al. (2012). The animat new frontiers in whole brain modeling. IEEE Pulse, 3.
  6. Barron, A. B., & Klein, C. (2016). What insects can tell us about the origins of consciousness. Proceedings of the National Academy of Science of the United States of America, 113(18), 4900-4908.

 

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