Disclaimer: I'm not an expert in animal physiology or psychology so I don't intend to present this as a rigorous description of animal suffering.
I think that it's reasonable to assume that the degree to which something can experience suffering is proportionate to the sophistication of its ability to think.
When I'm playing a video game, enemies respond to my attacks and attempt to keep from dying. However, we generally don't consider that suffering because we don't believe that the associated program has a concept of pain.
Simple animals appear to be able to experience pain. However, they might not be able to experience suffering as a condition. That is they don't appear to be able to creatively imagine and dread pain.
More sophisticated animals (e.g. dogs) appear to be able to understand suffering in a psychological sense.
Very sophisticated animals, most notably humans, can also understand suffering more philosophically. E.g. by understanding the way that suffering is preventing them from reaching their longterm goals, how suffering could be due to injustice, etc.
My point here, is that while it is clear that virtually every organism avoids death, it is not necessarily clear in which of these or other senses they experience suffering. My understanding is that it was previously thought that insects were more like the computer program: able to avoid injury but without actually having an experience of pain.
I think that it's reasonable to assume that the degree to which something can experience suffering is proportionate to the sophistication of its ability to think.
When I'm playing a video game, enemies respond to my attacks and attempt to keep from dying. However, we generally don't consider that suffering because we don't believe that the associated program has a concept of pain.
Simple animals appear to be able to experience pain. However, they might not be able to experience suffering as a condition. That is they don't appear to be able to creatively imagine and dread pain.
More sophisticated animals (e.g. dogs) appear to be able to understand suffering in a psychological sense.
Very sophisticated animals, most notably humans, can also understand suffering more philosophically. E.g. by understanding the way that suffering is preventing them from reaching their longterm goals, how suffering could be due to injustice, etc.
My point here, is that while it is clear that virtually every organism avoids death, it is not necessarily clear in which of these or other senses they experience suffering. My understanding is that it was previously thought that insects were more like the computer program: able to avoid injury but without actually having an experience of pain.