I'm no expert, but I just scrolled through the Wikipedia article for Eusociality, because I know that's a really interesting topic in the field you describe, and then picked out all the links to scientists:
And well, descriptive words that get mentioned relatively often: entomologist, biologist and sociobiologist.
Sociobiology is almost a competing theory to sociology, though, in that it tries to explain social behavior with evolution.
The Wikipedia article on sociology does say rather strongly that it is about humans.
My best guess is that while e.g. eusociality would offer a broader range to study, I guess, humanity is just not as interested in the specific details, as they are when studying humans. So, that's why sociology for animals is presumably not a field of its own, but rather lumped into entomology/biology.
Thanks for the pointers, I'll have to give'em a look! Eusociality does sound right in line with what I was wondering about, but hadn't heard of it before!