Many people, myself included, find it plausible that suffering of a certain intensity, such as torture, carries greater moral significance than any amount of mild suffering. One may be tempted to think that views of this kind imply we should primarily prioritize the beings most likely to experience these “lexically worse” states of suffering (LWS) — presumably beings with large brains.* By extension, one may think such views will generally imply little priority to beings with small, less complex brains, such as insects. (Which is probably also a view we would intuitively like to embrace, given the inconvenience of the alternative.)
Yet while perhaps intuitive, I do not think this conclusion follows. The main argument against it, in my view, is that we should maintain a non-trivial probability that beings with small brains, such as insects, indeed can experience LWS (regardless of how we define these states). After all, on what grounds can we confidently maintain they cannot?
And if we then assume an expected value framework, and multiply the large number of insects by a non-trivial probability of them being able to experience LWS, we find that, in terms of presently existing beings, the largest amount of LWS in expectation may well be found in small beings such as insects.
* It should be noted in this context, though, that many humans ostensibly cannot feel (at least physical) pain, whereas many beings with smaller brains show every sign of having this capacity, which suggests brain size is a poor proxy for the ability to experience pain, let alone the ability to experience LWS, and that genetic variation in certain pain-modulating genes may well be a more important factor.