My last post created quite a buzz among ethical vegans who categorically declare that it's wrong to harm all animals unnecessarily-insects included. Trust me when I say that I understand how raising doubts about insect sentience makes vegans uncomfortable. Angry, even. Any line drawn through the animal world bearing on the extent of our moral consideration is a line that cuts right into vegan identity politics, complicating as it does the entire concept of veganism as an activist response to systemic injustice.
All that said, here we go. I want to suggest here that insects do not warrant our moral consideration because they do not feel pain, or at least anything qualitatively comparable to what farm animals experience when they suffer. Of course, I cannot make this case with airtight certainty (nobody can)-do note, though, that the same can be said for the plants we eat-but my reading of the evidence (an ongoing process that leaves me open to change) currently compels me to argue that insects are legitimately (ethically speaking) edible. We can, in essence, put them to good use in ways that reduce the harm we cause to animals who we know without a shadow of a doubt suffer. And if we can do that, we should. We are, in other words, not only justified in eating insects. We are obligated to do so.
Begin with anatomy, which is essential to pain. Pain is a sensation that goes beyond the stimulation of neurons. The stimulation of neurons might elicit a response that appears to be a reaction against pain. But, considering insects' primitive anatomical state (compared to animals that clearly suffer), we cannot necessarily trust the external appearance of such a response, much less impose upon it a narration of pain.
As the International Association for the Study of Pain (IASP) explains, pain is an emotional and subjective experience, one that requires a higher ordered, much more complex nervous system. Insects lack this. They have nothing remotely close to it. Specifically, they do not have the nociceptors that transmit pain signals through our spinal cords and to our brains where the thalamus sends those signals into the limbic system for interpretation. Because insects lack the structures that foster this process-one that's essential to feeling pain-they lack the ability to experience pain subjectively and emotionally.
Considered from an evolutionary perspective, the matter of insect pain is that much less plausible. It makes perfect sense for insects-given the biological niches they occupy, their existence as a social collective (most of the time), their relatively brief lifespans (a matter of days in some cases), and their sheer numbers-to lack a pain apparatus. We assume too easily that pain is essential for biological survival. This claim might hold true for an individual, survival-of-the-fittest view of life, which many animals require. But the collective survival of a species (such as insects) could conceivably benefit from the exact opposite: not feeling pain. Several insects propagate themselves through cannibalistic mating practices. Most famously, the female praying mantis will bite off the male's head mid-coitus. Within the male's head you do not find a brain, but rather a little enzyme package that protects the female if copulation is successful. From an evolutionary angle, pain would (to say the least!) inhibit this critical, if weird, symbiotic process.
Taking this logic even further, consider what pain accomplishes for the animals that experience it: it teaches them how to solve problems. This implies a life-span that accommodates a pain-driven learning process. Pain, after all, is integral to a trial-and-error process of negotiation with the external world. I would argue that one of the reasons that insects breed so effectively is to avoid trial-and-error-which can be resource wasteful-altogether. Problems, instead, are solved collectively through breeding efficiency, not through an individual insect drawing on pain to get it right the next time. In essence, insects have no evolutionary need for pain.
The default move here is to argue that we should err on the side of caution and assume they have a pain sensation. To do this, though would also require, given the research done on the behavioral responsiveness of plants, that we take the same precaution for plants. That we cannot do. Moreover, provided the pain that would be spared to obviously sentient animals if we transitioned to an insect-based diet, it would be irresponsible, or something close to it, for us to project the capacity for pain on animals that have no evident apparatus for experiencing it, much less an evolutionary reason for doing so.