Saturday, September 3, 2016

Do Insects Feel Pain? A Revealing Question

At some point in their career, every entomologist will be asked the question "do insects feel pain?" A surprising amount of research has gone into answering that question or, in some instances, unrelated research has provided insight into that query. My answer to that question has more to do with the person asking it, and as far as I know, that is a unique response.

Questioning the capacity for insects to feel pain says more about the one who intends to inflict it.

As one who interacts with the public more than many entomologists, it has become evident that while some people have no qualms about ending the life of an insect, even advocating extremely inhumane techniques ("Kill it with fire!" is a common reply to someone else's social media request to identify a household insect), there is an increasing tolerance for insects, even in the home. If the creature is unwelcome, there is now often a plea for a non-lethal means of dealing with the uninvited arthropod.

The flipside of this more empathetic response to "bugs" is the question of whether insects feel pain. The obvious, hoped-for answer is "no, they don't." The person asking is then relieved of guilt for harming or killing any insect in the past, present, and future. So, while the new trend is for more people, especially women, to seek humane methods of insect control, many people still look for examples of how insects do not deserve empathy and compassion as a way to vindicate their own behavior towards other organisms.

The bottom line in the question of whether insects feel pain is thus the unspoken question of whether killing insects and spiders falls into the category of cruelty to animals. Legally, it would be difficult to argue that insects, being animals, are exempt from that crime. Obviously, this is not the case, and I do not see that implied public consensus changing anytime soon. Swatting a mosquito could be an act of "self-defense," though, considering the atrocious diseases that those biting flies can transmit.

Ok, so you want a scientific answer? Most entomologists I know resort to the short answer that insects do not have "pain receptors" like higher animals. This means they have no nerve cells devoted to the perception of pain. Insects can sense heat and cold, for example, and various chemical and tactile stimuli, but not pain as we would define it.

Is the wasp feeling no pain while being killed by the spider?

The fact that many insects, and other arthropods, willingly sacrifice limbs and other body parts in order to survive predator attacks is a testament to how apparently immune to pain they can be. A missing leg hardly slows down a grasshopper. Tattered wings rarely encumber a butterfly finishing its mission of mating and procreation.

As a colleague and fellow blogger noted in his own treatment of this question, another important aspect of physical pain is the emotional distress that comes with it. Ascribing human emotions to non-human organisms is known in the scientific community as "anthropomorphism," and is considered a big no-no when attempting to conduct unbiased research and observations. So ingrained is the concept of avoiding anthropomorphism that we now have to question whether the unemotional conclusions we draw in animal behavior studies are really the correct ones. The truth probably lies somewhere in the middle.

The fact that people are asking questions like this that leave open the possibility that insects and other arthropods are sentient beings is a hopeful sign, regardless if that belief is based in reality. We could certainly stand a little more empathy for other living things. Then again, look how we treat other members of our own species.

Source: Ballenger, Joe, 2016. "Do insects feel pain?," Ask an Entomologist.


  1. Somewhere in there is some cellular response to damage. Even if an insect does not "feel" it like a human does, there's got to be some form of chemical response. Do insects have stress hormones? Do they "feel" scared? I have little doubt that the capacity for such responses is very simple compared to larger organisms with more sophisticated nervous systems, but in the end we're all still machines made of vast numbers of cells communicating with chemicals and electrical signals. We're privileged to be able to ponder these dilemmas.

    1. Wow. I hope *everyone* reads your comment. One of the most eloquent paragraphs I've ever read. Thank you!

  2. Here's another blog post I found covering this issue:

    My two cents: I think this issue, along with similar issues such as "can animals [mainly mammals] feel emotions," comes down to definitions of the words we use to describe a phenomenon. Before we can say an organism has "X," we must define "X." Scientists do define these words, but the problem lies in the fact that scientists will define words differently from paper to paper and through time. How can one definitively say, for example, "Do insects feel pain" if the concept of "pain" has several differing definitions? How a person responds to that question depends solely on what definition they’re using, but the problem is most people don’t define the word for the person asking the question, they simply answer the question in a yes or no manner. There are “set” definitions that the majority of scientists will use oftentimes, but just because the majority uses it doesn’t mean everyone uses it.

    You hit on another concept I want to comment on as well. “Ascribing human emotions to non-human organisms is known in the scientific community as ‘anthropomorphism,’ and is considered a big no-no when attempting to conduct unbiased research and observations.” Your comment covers what I believe is a massive problem in behavior research. Humans are animals. We are not something separate or anything more unique than any other species in terms of the evolutionary process. We share an evolutionary basis with every other living thing, and I think when scientists try to utterly separate themselves from “anthropomorphizing,” they’re inherently acting as if humans are a totally unrelated lineage in evolutionary terms. This line of thinking isn’t solving the problem, it’s just creating another problem. I greatly agree with you that the truth probably lies somewhere between the two extremes.

    Take for example two situations. In the first, a bear walks around the corner and a human becomes fearful of the much-larger carnivore and therefore responds by vacating the area. In the second, a bobcat walks around the corner and a squirrel, seeing the much-larger carnivore, responds by vacating the area. Many scientists would look at this interaction and probably be hesitant to say “well, the squirrel felt fear, so he ran away to avoid the potential danger,” and would instead say something along the lines of “In the presence of a carnivore, a squirrel will avoid interactions with it.” The first line of thinking would be deemed anthropomorphizing, but is it really? I know behaviorists are hesitant to seem biased in their descriptions, but as the saying goes, “if it looks like a duck, quacks like a duck, and swims like a duck, it’s probably a duck.”

    1. I agree with you on all points. Thank you for taking the time to write!

  3. When I studied insecticide toxicology, I tested sublethal doses of malathion on Peripleneta americana by teaching the roaches to run a Y maze, with electric shock on one arm and shelter on the other. It took 10 to 25 attempts with shocks for roaches to learn never turn left. They obviously reacted to the shocks and learned to avoid them. I think they felt pain. Sublethal doses of malathion at several doses apparently retarded learning. Details of this study are long lost, but I remember the roaches reacted to shocks.

  4. Being pragmatic, swatting a bug the way most people do shouldn't be considered the most "humane" way to do it? I mean, it's instant death, isn't it?

  5. Pain (usually a warning) needs to be perceived, then processed. So as scientists we look for receptors, usually peripheral. In organisms with exoskeleton we would expect them in sensory groves around hairs or at thin areas between the main hard plates. Known pain receptors are usually distinctly different from heat, chemo or pressure receptors and are more than just nerve endings. Structures like that have not been found in insects. Thus it is difficult to find neuronal pathways that would process input from these non-existent (?) receptors. To make it more difficult, insect nervous systems are much less centralized (cephalized)than those of vertebrates and even cephalopods and more organized on a segmental pattern. Is a short reflex arc that never involves higher processing to be called a pain reflex? It is impossible to prove a negative. So how about prove positive? Hymenoptera and flies produce a hectic unusual buzz when caught. It's easy to see that as a pain response. But in reality, it maybe a defensive threat from the stinging wasps and bees and a mimicry thereof in case of the defenseless fly. Electric shock examples - which show avoidance learning even in hydra and jellyfish (neural networks with no higher organization) are not really prove of pain reception. Electric shocks circumvent those receptors even where they exist, acting directly on the nervous system. Ask yourself: Does it hurt to touch a cattle fence? No, not really. Would you willingly do it again? usually also,emphatically, no.
    I think it is nice if the general public starts developing some empathy for 'bugs' but I still don't think we, as scientists, can support misinformation. I think the answer is 'Insects do not feel pain as we know it.'

  6. I had an interesting experience tonight. I walked into the kitchen to find a cockroach on the chopping board. This place is being torn down in two months, and I'm moving in a few weeks, so I thought "Why kill it?" I decided to trap it and release it outside, but in the process of trapping it, it attempted to flee, and the plastic container came down on it's leg (the second one from the front), and in response to that, the cockroach jerked backwards and it's leg got ripped off at the "shoulder". Previously when I've seen insects get a leg amputated, they haven't seemed to notice, but this cockroach immediately tried to get at the amputation site with it's mouth, and spent the next few minutes preoccupied with this, to the extent that it rolled over on it's side as far as it could without falling on to it's back, to get to the site. It seemed to truly be in discomfort, and I've never seen an insect act in such a manner before. I made a video of it.