I cannot find any resources in regards to this. They all basically seem to think that there is no such thing as an animate, neuter, noun in Russian. This came up because I have a grammar book which says that in accusative, animate plurals take the form of genitive plural but shows насекомое becoming насекомых when I would've expected it to become насекомоей. I spent a good hour trying to find somewhere that shows you why this is not the case, but haven't yet found one. I asked several other native speakers for an explanation but they didn't know.
So, here it is according to them:
чудовище -> чудовищ
животное -> животных
млекопитающее -> млекопитающих
насекомое -> насекомых
With only four words to work with, the only pattern I can see is that if the word ends in two vowels (ое, ее), you change them to -ых/-их, else you just drop the vowel; or basically like a neuter adjective. Perhaps you could shed some light on this subject for me or point me in the direction of a resource that covers this?