An interesting article about whether invertebrates feel pain is out on the New Scientist website.

Apparently even the simplest crustaceans show pain-related behaviours, like favouring wounds. Interestingly however, insects do not. Though that's not really new information.

What's new is that they have an argument for why this could be. It's that evolution would favour using limited neurons for things other than emotional pain response in creatures that lived very short lives.

What does this mean for our considerations? It suggests that some r-selected species that live generally short lives are less likely to feel pain emotionally than K-selected species who can live longer lives and will benefit more from having an emotional response to pain. The shorter the average lifespan of a given species, the less likely they are to actually feel pain and count for much suffering. So it seems at least, that wild animal suffering may actually be less than some initial approximations, assuming that the majority of insects actually don't feel pain on an emotional level.

To borrow from the calculations I was playing with earlier, it would be equivalent to giving those insects zero pain structures.

It also means, if you assume that longer lives tend to be worth living more than shorter ones, that the species who's lives are least likely to be worth living, are also the ones that are most likely to not actually suffer.

Edit: Though the facts about how cockroaches appear to suffer when socially isolated suggest that they may actually have an emotional response to certain kinds of psychological pain, but not physical pain. So it may be possible that those insects that don't suffer from physical pain, can still suffer in ways not associated with physical pain. Cockroaches may be an exception though, as they can live for over a year, and have a million neurons to work with. So it's possible that it really depends on the species of insect or invertebrate.

I'm interested in suffering in general.

Here's my test: Find something you suspect they don't like. Every time they do a certain action, do that thing. If they stop doing it, they're suffering.

I'm interested in suffering in general.

Here's my test: Find something you suspect they don't like. Every time they do a certain action, do that thing. If they stop doing it, they're suffering.

That would be evidence of learning, but I'm not sure it actually shows suffering. It may just show that they don't like that thing, whatever it is, not that it actually causes them emotional suffering. What you're suggesting sounds like Positive Punishment Operant Conditioning, or even simple Classical Conditioning. I'm just thinking that humans don't like very bright lights or loud noises, and you can easily condition a human to associate for instance, a rabbit with a loud noise and make them dislike the rabbit as well. But I don't know that I would say this causes actual suffering. If you consider the fear response to scary noise to be suffering, then I guess so. But clearly, this is different from an emotional response to physical pain.

Though it does appear you can classically condition insects, so it may well be the case that they can suffer in a very loose sense.

So... It may well be that insects can suffer in certain ways, in the sense that they can have negative emotional states. But these states might be detached from their experience of physical pain. So it would be like someone with Congenital Insensitivity to Pain, though not really, because insects seem to sense pain, they just don't appear to care about it like we do. Even so, they might still suffer for other reasons, like social isolation, or some other emotional state where they "feel" bad. Perhaps a bee feels bad if it fails to achieve it's goal of foraging for nectar.

Hmm... If we assume that positive and negative emotions are required to motivate a sentient being to action, then insects probably do "suffer" to the extent that they can experience negative emotions. However, if they don't experience negative emotions from direct physical pain, they probably suffer a lot less from the process of death and physical injury than other more sensitive beings. As a large amount of the suffering that it is claimed wild animals experience, has to do with such things, it suggests that an insect being eaten by a spider, probably suffers less than a gazelle being eaten by a lion. Sure they both have their hopes thwarted (to whatever extent they had hopes), but while the gazelle is in extreme physical and emotional pain, the insect is probably mostly confused as to why it can't move anymore and is receiving signals of danger. Perhaps once it realizes what is going on, it becomes sad at its fate. But so long as it doesn't actually feel the physical pain of dying, it's acute suffering is going to be much more subdued than the gazelle's shocking distress. Though again, I don't know what actually goes on in the head of an insect or gazelle being eaten, so this is all just conjecture.

But you do make a good point that it's suffering in general, rather than just the emotional response to physical pain that we should be considering.