Not that it's "not allowed," specifically (as far as I know, anyway) but rather that Western art generally isn't the purpose of Danbooru, and so the majority of it doesn't get approved.
I doubt this will be approved before the three-day limit ends.
They're not really all getting it on with each other so much as lying in a grotesque heap while some lucky few get to interact with some human maidens, no?
Although, I admit it would be much better if it was a bit bigger. One cannot fully appreciate the squiggly, squirmy awesomeness of stuff like that in such a small resolution. Drawing bugs is all about the details.