Also regarding the soldier and the doctor: I thought the mayor did rape the doctor, hence why his privates were bloody. I thought the mayor had raped her, then pulled down her dress. After all, it was a scene staged specifically for the soldier's benefit.
I had thought that it was possible that there was forced sexual entry of a... different sort, given the incisions in her neck and chest. That felt like a reference to the titular screwflies, who had been altered so that the male mated with the wrong body part.
Honestly, that felt like a bit of an inconsistency. It was quite clear that the men weren't becoming rapists - in fact, they were becoming strangely asexual. This wasn't sexualized violence, it was gendered violence, which is part of what made it so eerie. We're pretty inured to sexualized violence in our society, but I think that gendered violence - for example, those women who were gunned down by that maniac
because they were women (now you're all going to say "which girl-gunning-down maniac do you mean" and I'm going to reply "I don't want to live on this planet anymore") - still bothers us. But then there's the scene with the mayor, and it leaves a lot of questions.
My take on it was that one of two things happened:
1) There was a greater degree of sexualization to the killings than the narrator was reporting, but since all the narrators were more or less unreliable - even the main characters were restrained by not wanting to write about gory details before things got bad, or not wanting to bother writing about the horrible truths once it was too late to do anything about them anyway - it had to be implied sideways, which Tiptree did through the mayor scene. In this case, I'd call it Tiptree's only mistake in the story. I understand wanting to make the references to sexualized murder oblique, to account for the sensibilities of the characters, but if all you're going to do is imply it, you've got to do it more than once, especially if the rest of the content seems to imply that violence is replacing sex, not being added to it (and really, if violence was just being added to their sexual desires, why didn't they just all become kinky?).
2) The killings were more sexualized in an original draft, and Tiptree missed it in the mayor scene in an early draft.
Don't take this as serious criticism - I loved the story. But... the mayor scene did seem a bit odd to me.