According to Calvin, at least, the same as to be a bat. But for the rest of us, it seems obvious that there is likely to be a qualitative difference between the subjective experience (if any) of a bug, and that of a bat. And, if true bugs don’t work for you in this example, there’s always the colloquial “bugs” such as bacteria and viruses, which presumably don’t have any experience at all.
The reason I make this point is that it’s long seemed to me that there’s a sorites problem with the ordinary person’s intuitive understanding of consciousness (at least for mine). In that understanding, either an entity is conscious or it’s not, but when you look at the “Great Chain of Being” from viruses to humans, there’s no obvious point at which to draw the line. I thought that Thomas Nagel’s famous paper on “What is it like to be a bat?” might address this problem, but as far as I can see he skates straight over it. Nagel takes it for granted that bats “have experience”, different from ours mainly in the consequences of having different senses and living in a different environment.
His closest approach to the sorites problem is to say that “I have chosen bats instead of wasps or flounders because if one travelstoo fardown the phylogenetic tree, people gradually shed their faith that there is experience there at all. ” But the gradation here is in people’s beliefs. As I read Nagel, animals either have experience or they don’t, it’s just that, while we’re sure about bats, and presumably, in the other direction about viruses, we don’t know about wasps. But does Nagel really believe that at some point in evolutionary history, a light flicked on in a brain somewhere, and the first experience was had? He doesn’t say, and a (not very competent) search on my part failed to find much in the way of answers.
I guess this wouldn’t be a problem for someone like Dennett, whose account of consciousness seems to me to be consistent with a gradual expansion in complexity, analogous to the standard story about the evolution of vision. But I honestly don’t know whether that’s right and whether Dennett’s critics (who seem to be fairly numerous) have a better answer to this problem.