The last two questions we tackled revolved around the cognitive abilities (communication, and personality) of arthropods, specifically insects and spiders. These are really tough questions to tackle because a lot of people, even (especially?) those who genuinely like insects and spiders, want to humanize them as a way to identify with them.
I think it’s a good thing to want to identify with these animals, so long as we’re making proper comparisons. Sometimes, however, this very human impulse can get us into trouble…like this Twitter post by the Featured Creature twitter account.
Jumping #spider holding its baby. < This. This is how you turn a spider #hater into a spider #lover. pic.twitter.com/g7kmyHwcYo
— Featured Creature (@ftcreature) July 22, 2013
This image is typically shared as an example of maternal care in jumping spiders. Although maternal care does exist in this group, it doesn’t typically involve the mother carrying them to a new location in the manner shown.
Assuming the picture is real (see Chris M. Buddle’s comment), the activity pictured here is most likely cannibalism. Instead of being an endearing picture, this is more of an example of how our desire to identify with insects and spiders can cloud our image of how they behave. This desire has a name, it’s called ‘anthropomorphism’…which means to imbue human characteristics or motivation onto non-human organisms.
I wanted to open our discussion of insect pain up with that story, because it’s a very important point to make. Insects react to the world differently than we do, and when it comes to cognition it’s very difficult to separate our motivations from theirs.
Separating Pain and Sentience
The first thing I think we need to do is to define ‘pain’, because it’s not as simple as avoiding injury. During the deepest stages of sleep, people still toss and turn to avoid putting themselves into potentially damaging positions…even if they don’t remember the experience. We can also react to stimuli without feeling it, using a reflex arc. It’s possible to avoid injury without experiencing pain as we understand it.
The people who study pain in humans have a pretty useful definition of pain, which differentiates between experiencing pain and avoiding injury (which is termed nociception). You can read the full definition here, but I’ll remove the relevant snippets:
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
…
The inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment. Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life.
…
This definition avoids tying pain to the stimulus. Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state, even though we may well appreciate that pain most often has a proximate physical cause.
Although it might seem to be a little nitpicky, we really should separate pain and nociception. After all…bacteria can avoid toxic substances just as well as animals can.
Insects and Injuries…what do we know?
We know that insects can avoid injuries, and sense most potential sources of damage. The best studied nociceptor is the Drosophila nociceptor TRPA1, which is pretty closely related a gene in mammals which has an identical function. It senses pressure and heat, and reacts to the chemicals which make peppers hot (capscaicin) and mustard spicy (isothiocyanate). I’m not sure how widespread this protein is, because there have been gains and losses in some nociceptors. It’s also found in beetles, so painless appears to be somewhat widespread.
Different animals use different receptors to sense different things. Drosophila is repelled by the taste of wasabi, but crayfish are not. Additionally, crayfish do not react to the type of burn that dry ice produces when you get a wart burnt off at the doctor’s office. They do, however, respond to heat. It’s very likely that crayfish have TRP receptors, but it seems they use different receptors than fruit flies and humans use.
Pain and Emotion
Pain is ultimately an emotional response, so the question of whether insects feel pain as we would understand it really depends on whether they feel emotion. This is where scientists run into problems with the whole ‘do insects feel pain’ question.
There’s a rather obvious philosophical issue which needs to be mentioned, The Problem of Other Minds. I’m not going to spend much time on this, because we can avoid that issue by comparing the behavior of injured insects to injured mammals. Mammals, being animals we *know* feel pain, are the positive control here.
It’s important to note how Drosophila defends itself against parasitic wasps. It does this by rolling over them, which makes it impossible for the wasps to get enough leverage to pierce the larva’s exoskeleton.
Mammals have a diverse response to pain, often avoiding use of the injured area and responding to different types of pain differently. Drosophila, on the other hand reacts to many different insults by rolling towards the thing that hurts.
If you poke the larvae with a needle, stick them with a soldering iron, bathe them in blue light, or put them in hot water…it’s always the same response they have to the wasp ovipositor.
That being said, we can make some further observations about how insects learn to avoid bad situations. Drosophila can be conditioned in a manner to the famous Pavlov experiments. The gene White, which we talked about when we spoke about personality, appears to regulate how extreme the fly experienced a situation. Some White mutations, in addition to regulating some aspects of the fly personality, appears to make flies overestimate how bad the experience was. They learn to avoid stimulus associated with shocks quicker, and un-learn the association slower than flies without the mutation. This only happens with bad memories, though. If you reward (rather than punish) the fly, the White mutants perform pretty similarly to non-mutants.
Interestingly, the human equivalent of White is involved in panic disorders in humans.
Bringing it all together
With this topic there’s a million different ways we could go with this, and there’s just not enough room on this blog to go through all of the required material in detail. While researching this article, I found a diagram which sums up this topic rather nicely:
Image Credit: Sneddon et. al 2014
Drosophila does a lot of things in this graph which indicate the presence of pain. It…
- can sense when it’s injured, using equipment similar to mammals.
- can learn to avoid bad things, and seek out good things
- can differentiate degrees of ‘good’ and ‘bad’ experiences.
However, fruit flies don’t seem to…
- Have appropriate responses to different degrees of injury
- Employ mitigating behaviors, such as rubbing, limping, or guarding the injury.
So it’s likely that Drosophila doesn’t feel pain…because it doesn’t match the positive control, right?
Well, the tobacco hornworm can also do all these things…but it has responses which are more mammal-like than Drosophila.
Noxious stimuli to anterior or posterior segments can evoke a transient withdrawal (cocking) that precedes a strike towards the source of stimulation and may function to maximize the velocity of the strike. More intense noxious stimuli evoke faster, larger strikes and may also elicit thrashing, which consists of large, cyclic, side-to-side movements that are not directed at any target. These are sometimes also associated with low-amplitude quivering cycles. Striking and thrashing sequences elicited by obvious wounding are sometimes followed by grooming-like behavior.
There’s also some evidence of self-medication in insects, which usually involves ingesting substances that have a negative effect on their development. So they’ll pay a cost to access some sort of mitigating measure, when it comes to parasites or illness. Drosophila happens to be one of these insects.
The Bottom Line: Do Insects Feel Pain?
This article, for me, was one of those really weird articles where I think my opinions changed while doing research for the article. The typical position of entomologists is that insects feeling pain is pretty unlikely. In the past, I’ve argued a position stronger than the one that Bova argues in his piece…one which was based upon the information similar to what Bova received during his undergraduate training.
However it now appears to me that a lot of the pathways insects use to not only sense injury, but interpret these experiences, and respond to that injury are a lot more similar to my pathways than I had originally realized. The paper on hornworm responses to pain was something I was unaware of, and have never had the opportunity to observe in person. The grooming behavior is what interests me, and it doesn’t seem to have been addressed further in the literature.
So based on all of this new information, my response has gone from outright skepticism to something more akin to:
¯\_(ツ)_/¯
Insects are a very diverse group, with biology that can vary widely between all groups. I would not expect every insect to interpret the world the same way, because they do not all have the same level of complexity.
Among insects, most of the pieces of the evidence required to say that insects feel pain appear in some groups to some extent. However, they do not appear in all groups to the extent which would result in a definitive answer. It would not surprise me to learn that some insects, particularly some of the social insects, would posses all the pieces of evidence.
While we can’t say for sure with our current state of knowledge, it seems that the field of insect nociception may be heading in that direction.
Works Cited
- Abbott, J. (2014). Self‐medication in insects: current evidence and future perspectives. Ecological Entomology, 39(3), 273-280.
- Barron, A. B., & Klein, C. (2016). What insects can tell us about the origins of consciousness. Proceedings of the National Academy of Sciences, 113(18), 4900-4908.
- Bentley, A. J., Newton, S., & Zio, C. D. (2003). Sensitivity of sleep stages to painful thermal stimuli. Journal of sleep research, 12(2), 143-147.
- Diegelmann, S., Zars, M., & Zars, T. (2006). Genetic dissociation of acquisition and memory strength in the heat-box spatial learning paradigm in Drosophila. Learning & Memory, 13(1), 72-83.
- Gerber, B., Yarali, A., Diegelmann, S., Wotjak, C. T., Pauli, P., & Fendt, M. (2014). Pain-relief learning in flies, rats, and man: basic research and applied perspectives. Learning & Memory, 21(4), 232-252.
- Gherardi, F., Aquiloni, L., & Tricarico, E. (2012). Revisiting social recognition systems in invertebrates. Animal cognition, 15(5), 745-762.
- Kim, H. G., Margolies, D., & Park, Y. (2015). The roles of thermal transient receptor potential channels in thermotactic behavior and in thermal acclimation in the red flour beetle, Tribolium castaneum. Journal of insect physiology, 76, 47-55.
-
Milinkeviciute, G., Gentile, C., & Neely, G. G. (2012). Drosophila as a tool for studying the conserved genetics of pain. Clinical genetics, 82(4), 359-366.
-
Nakamura, M., Ueno, S., Sano, A., & Tanabe, H. (1999). Polymorphisms of the human homologue of the Drosophila white gene are associated with mood and panic disorders. Molecular psychiatry, 4(2), 155-162.
-
Puri, S., & Faulkes, Z. (2015). Can crayfish take the heat? Procambarus clarkii show nociceptive behaviour to high temperature stimuli, but not low temperature or chemical stimuli. Biology open, BIO20149654.
-
Sneddon, L. U., Elwood, R. W., Adamo, S. A., & Leach, M. C. (2014). Defining and assessing animal pain. Animal Behaviour, 97, 201-212.
-
Tobin, D. M., & Bargmann, C. I. (2004). Invertebrate nociception: behaviors, neurons and molecules. Journal of neurobiology, 61(1), 161-174.
-
Walters, E., Illich, P., Weeks, J., & Lewin, M. (2001). Defensive responses of larval Manduca sexta and their sensitization by noxious stimuli in the laboratory and field. Journal of Experimental Biology, 204(3), 457-469.
Ask an Entomologist 
THE ONES I HAD IN MY 55 YEAR OLD MATTRESS IF INJURED 1 IT WOULD CHARGE ME.I THINK THAT ANSWERS YOUR QUESTION. ALL I HAD TO DO WAS ROLL OVER IN BED AND GET A STING. THEY WERE CAMOUFLAGED LIGHT GREY WITH SPARKLING BUNCHES OF LEGS ON EITHER SIDE .THEY ALSO HAD 2 BLACK SPOT EYES AND 2 WINGS ON EACH SIDE WITH A LOBSTER SHAPED TAIL. SOME WERE 1&1/2 INCHES LONG. IF THESE WERE WERE FOUND OUT BY HOLLYWOOD THEY WOULD MAKE A GREAT MONSTER WITH ALL THE LEGS ON THE SIDES AT THE FRONT AND IF ANGERED WOULD KILL SMALL INSECTS AND IF HUMAN SIZE –I DO NOT EVEN WANT TO THINK ABOUT THOSE UGLY NASTY THINGS BEING ANY BIGGER.
LikeLike
MY QUESTION IS ARE THEY RELATED TO SCORPION FLIES? A BOOK I HAVE FOR A LONG TIME READ THERE ARE OVER 1,000 VARIETIES OF THOSE FLIES.
LikeLike
THEY SEEMED TO HAVE A WHOLE ENTOURAGE OF FLIES AND LITTLE HARD SHELLED INSECTS WHERE EVER THEY ARE. IT IS REALLY STRANGE THE ADULT ONES ARE MUCH SMALLER AND HAVE FEWER STINGING LEGS. I BROKE A FLY SWATTER ON THEM NIGHT AFTER NIGHT SEALING THEM IN UNTIL BLEACH KILLED THEM. ANT AND ROACH KILLER DID NOTHING. THE BIGGER ONES WOULD COME OUT AND IMMEDIATELY FIND A DEAD 1 AND BEGIN TO EAT IT.
LikeLiked by 1 person
These studies appear to be done on larvae and adults. Do pupae feel pain?
LikeLike
Why are you shouting? Those insects sound interesting. I might draw them.
LikeLike
Just out of curiosity, I caught a fly, and broke a leg off. Not trying to hurt it, just an experiment. The fly didn’t appear to have any pain, the next day, I broke another leg off. Still not appearing to be in any pain. It was still flying. Then I put it in the freezer, after it froze, I took it out of the freezer, it thawed out and flew away. My conclusion was that flies do not experience pain. Not sure about other insects, but with the small size of their brains, I do not believe they have the capability of of experiencing pain.
LikeLike
It should be considered that nociception as a withdrawal or escape behavior motivator is quite obvious in brainless creatures. But sweeten up the spot and it will keep coming no matter how many times you zap it (eg, bait a window glass with a bit of sugar and see how a fly keeps coming back for the sweetness. It’s not dumb it just feels the sugar more than suffering noxious stimuli. Given the escape but not avoid reaction does not mean that the fly doesn’t feel pain, causing it to fly away, but that it doesn’t suffer so it keeps coming back for the sweet. Spiders and all other fly-catchers count on that so they wait for the inevitable return. Had the fly suffered, return would not have come so quickly; so not suffering but arousal of defense circuits is what pain does. Indeed, many insect species while being eaten from the back keep eating after escape proves futile. But we recognize pain by the attempted escape reaction, though only suffering leads to long term defense and avoidance. Yet we can be like flies too. In fact we know that with certain lesions in the CNS people do not feel pain, nor will they engage in withdrawal movements. Indeed, some feel pleasure where you feel suffering pain. Other lesions cause all the defense and escape behaviors but not avoidance. While with other lesions victims will withdraw but not know why. To suffer, animals must have a certain number of neuronal circuits We now have robots that upon signal of damage become hyperactive as programmed to rapidly engage in repair programs. On the other hand, we see seizure like activity in flies (intense seemingly purposeless movements) which like post-ichtal behavior are exhausting but do not seem to alter behavior patterns. Injury seems to cause a lot of motility, but does not seem to produce learned avoidance. Therefore, no lingering evasion lessons seem to have been learned as the attractive power of a nociceptive experience does not seem to provoke avoidance. For example, spray a fly with Lysol (ammonia) spray, a costly experiment, and it will constantly return to a sugar coated spot. But a bee, ah that’s a real genius!
Lastly, endogenous endorphins do cause some to tolerate amazing pain. Some people have no pain too but they die young due to an amazing degree of self injury. However,hen you see the suffering of people with terminal cancers, for example, you realize that nature doesn’t give a damn. Suffering went way beyond pain for one reason: why not? The genetics of evolution is heartless to its errors as DNA changes randomly.
LikeLike
Upon common sense observances, insects are capable of emotions like fear or love. You can see their attractions towards one another. Capturing an insect elicits immediate flight and panic responses, but after gentle handling, the animals calm down. Helping an injured insect back to health will earn total trust and friendship with that individual. So, they are complex beings capable of emotion. Scientist contend that you need that to feel pain. Really? Anyway, as far as pain goes, yes, there are definitely signs of that. For example, in rescuing an injured butterfly, who I’ll name Sunset, unable to move one wing, I could see that pain would keep him from using it, just like we won’t walk on an injured foot. Upon one week of care and therapy, Sunset eventually made a full recovery. During the healing process, I noticed that the wing was not used because of pain, which prevented further damage. Only severe pain can imobolize you at a time when you’d rather get away. As healing began, the wing was used increasingly more. Trust developed quickly as Sunset learned that I intended no harm and didn’t mind my approach or handling, even when being launched into the air for flight lessons. Another example was with a cicada. They have a language that sounds like music to our ears. One particular call is definately an alarm. This can also be a signal of a painfull event. I’ll call her Rambo, for her markings. One day, I heard intermittent chirping and found her on the ground. I gently put her back on a branch only to see her fall off. Rambo was weak and frustrated, chirping weakly too. Then, I noticed her injury; a stab wound to her thorax. I figured she’d die soon from infection, so I dabbed a bit of tree tea oil on it. To our horror, it elicited an immediate reaction of pain, accompanied by thrashing, wing flapping and the most desperate cry I’ve heard from a cicada, worse than when they are snatched by a bird. This continued for five minutes followed by more intermittent chirps as she weakened from all of the trauma. I felt horrible and didn’t know how to stop the suffering that I just made worse. Hours later, Rambo was in heaven. If pain is an emotion, then insects definately feel both. If emotion is pleasure, they experience that too. Ever notice the female grasshopper during mating? Talk about exhibiting pleasure! But then there is the scientific evaluation that pain is an emotion and that they don’t see that in insects. First of all, many people can’t see emotion in any animals and question their abilities to feel pain. Then there are people who can’t see the pain and suffering that other humans feel. So, some scientists are overly analytical, to the point where they can’t see the obvious. Now, I can see both pain and emotion when observing insects and believe that they can be neurologically separate. Pain comes first, then the emotional response, if you have one. If pain is an emotion, then explain how I felt pain that woke me out of a deep sleep. My dream, at that time, had a different source for that pain than what was actually causing it. So, that shows that you don’t need a five pound brain to experience pain. You don’t even need to be conscious or emotional for that bad experience. Another example of this occurance was when I was still unconscious, comming out of the O.R. At that time, I was in intense pain and had been crying. After waking, the pain and my crying continued. Now I was unable to remember the unconcious experience until months later because of the drugs they had me under. So, scientists can be really blind to the obvious. They can injure their subjects without a flinch just by their callousness alone. They say that some insects don’t have nociceptors, needed for the sensation of pain. There can be more primitive mechanisms for that function. As I explained, not all of my pain is tied to emotion or to thought. Insects have brains connecting their nerves throughout their bodies, just like we do. They do react to touch, which means they can feel. We feel by pain. The more pain the greater the response. Im glad that your artical mentions the possibility that insects feel pain. If scientists can’t figure it out, they should at least say that we should insects the benefit of the doubt to avoid causing them great suffering.
LikeLiked by 1 person
I think the issue of sentience is an important one, and specifically perception of self. If I don’t feel consciously alive, how can I consciously feel? I’m merely responding, like a computer would.
LikeLike
“Pain is an emotional response”? Colour me incredibly sceptical. If it was true then having more control of your emotions would make it less painful to have one of your fingers cut off. Pretty definite it can’t. This sounds like one of these stories some humans tell themselves because they want to feel unique and completely different from any other animals. Which won’t work anyway as there’s already plenty of evidence of other mammals mourning dead group members for instance.
LikeLike
You are mistaken. Hypnotism can (and does) make things less painful, even surgery that would normally require a general anaesthetic! Also it is possible to be unaware of an injury at the point it occurs and only begin to sense the pain when you are conscious of having been injured. How can that be explained if pain isn’t an emotional response?
LikeLike
Pingback: Χορτοφαγία και βίγκαν ιδεολογία. Ποια είναι τα υπέρ και τα κατά; (part 3) – Enallaktiki Gnomi
Pingback: So why DOES anesthesia work on plants? | Ask an Entomologist