> very few animals other than these exhibit eusociality (humans aside,

Technically, humans are not eusocial, which by definition requires a biological division of reproductive labor. Most eusocial species actually have significant morphological differences in their classes (i.e. females that physically can or cannot reproduce).

Wilson tends to repeat the idea of humans and other primates as eusocial which I find confusing.

Eusociality and its evolution is indeed a fascinating topic. There are some great discussions on this from WD Hamilton (the study of led him to inclusive fitness theory and kin selection) and Richard Alexander (who discovered the only eusocial mammal - the naked mole-rat).