The study of weather arthropods can feel pain is a contentious issue, but it seems evidence is increasingly pointing towards yes. But there is something I noticed. Studies on arthropod pain focus almost entirely on decapods and pterygote insects. I ask, why? Of course it is neither possible nor practical to investigate pain in all 1.5 million+ known species. But why are entire classes and orders entirely ignored? Why has no one investigated in earnest weather scorpions, ticks, opilionids, isopods, amphipods, branchiopods, ostracods, centipedes, millipedes, silverfish, springtails, etc feel pain? Decapods and multiple pterygote insect orders show evidence of pain, but we have no idea if this is generalizable towards arthropods as a whole because none of the others have even been investigated much if at all. Personally I think more or less all arthropods feel pain with the exception of hyper degenerated parasites, but we can’t know until we look.
A particular case I think is relevant is silverfish and bristletails. Unlike winged insects, they molt continuously throughout their lives, and thus may have more capacity to heal injuries than things like flies. They also live rather long lives for insects, ranging from two to up to seven years. Doesn’t it make sense that the ability to feel pain and remember this feeling would be more beneficial for a long lived animal that keeps repairing its body rather than a short lived animal who’s regenerative capacity falls off a cliff after reaching reproductive age? A lot of non insects as well are rather long lived compared to similar sized insects. Bumblebee millipedes (Anadenobolus monilicornis) can live up to 5 years, which is quite long by insect standards.
Decapods for their part is almost a more egregious situation. At least with pterygote insects, species from multiple orders have been tested, so general statements about “insects” feeling pain are not entirely without basis. But a lot of sources say that “crustaceans” can feel pain, which is at best extremely misleading. “Crustaceans” have not been tested, just decapods. Nothing is known about pain in other orders and classes of crustaceans.
With all this at hand, why investigation the question of pain in Triops, Centruroides, Scolopendra, or Lepisma, rather than doing Drosophila for the ten billionth time?
“It doesn’t feel pain. It’s just a reflex.” is an argument that has floated around since… gods know when. And it hasn’t been solely towards non-humans. I remember that “babies can’t feel pain”-thing. As an autist, I keep running into the idea of “-autists don’t really feel pain. Um. We feel it differently to neurotypicals. Sure, I can provably walk with two broken feet, but a seam in clothes can cause enough pain to make me incapable of focusing on anything else and becoming forced to avoid moving in a way to increase it.
If a non-human doesn’t feel pain like majority humans, or react similarly, doesn’t mean it doesn’t feel pain. You can’t take a different kind of a nervous system, and apply another type’s criteria on it and then move the goal posts every time you are proven false. This has been continuously done with animal consciousness even during my lifetime and is still being done.
Study of pain in non-humans is a difficult subject for me, despite understanding the point in it in the current system. So yes, I think the OP makes a good case if it would help the idea to become generalizeable.
And yes, walking with broken feet did hurt like hell. It was just a different kind of pain, and tooth ache is yet another from the previous examples.
I would imagine something like Drosophila has an advantage that it is common and widely available, infrastructure and techniques are already in place for raising and studying it, it has proven to be suitable to the conditions of lab environments, and the basic physiology is well-understood, meaning that it is possible to build on that existing knowledge instead of starting from scratch.
I understand the sentiment. But we cannot have decapods and pterygotes be our only references for arthropod pain for all eternity.
At some point, you can only get so much insight from one species. Besides when testing all those other insects (and decapods), they were starting from scratch there too. So that begs the question, why are myriapods, chelicerates, apterygote hexapods, and non decapod crustaceans basically never tested?
I haven’t said it wouldn’t be important, but I’d rather find out the reasoning from someone who has publicly made statements suggesting that it is important, before drawing any conclusions. So, what practical differences would having this knowledge make?
Well, tarantulas and millipedes for example are semi popular pets and also commonly kept in captivity. Should welfare laws cover them? We cannot just extrapolate from crabs and fruit flies because there may be significant differences.
Thank you. That seemed like a good argument to me, so I thought I’d check it out to see what the animal welfare laws have to say in my country, the UK. Our key piece of legislation is the Animal Welfare Act (2006). It soon became apparent that this act, as written, only apples to vertebrates. It has been framed though, so that it is possible to “extend the definition of “animal” so as to include invertebrates of any description”, but this can only happen, “if the appropriate national authority is satisfied, on the basis of scientific evidence, that animals of the kind concerned are capable of experiencing pain or suffering”. I’m pleased to report that in 2021, The Act was extended to include decapod crustaceans and cephalopod molluscs. However, just as you state, that still leaves lots of animals unprotected. It still seems incredulous to me that any animal would be incapable of suffering, regardless or not of whether it experiences physical pain. I must concede though, that my assertion is far from scientific and is unlikely to cut any ice with lawmakers. I just hope that any studies undertaken with the ultimate aim of helping other classes of animal are proportionate, as there does seem to be somewhat of a paradox that we have to hurt animals to protect them from hurt.