Jason Castro contemplates it:
While there’s a good deal known about invertebrate neurobiology, these facts alone haven’t settled questions of their sentience. On the one hand, invertebrates lack a cortex, amygdala, as well as many of the other major brain structures routinely implicated in human emotion. And unsurprisingly, their nervous systems are quite minimalist compared to ours: we have roughly a hundred thousand bee brains worth of neurons in our heads. On the other hand, some invertebrates, including insects, do posses the rudiments of our stress response system. So the question is still on the table: do they experience emotion in a way that we would recognize, or just react to the world with a set of glorified reflexes?
The Dish 