Set- Yeah, there's fire resistance, but it's only 5 which, if I had to guess, is aimed at Alchemist Fire. Let's be honest... a party taking on a CR 7 creature ought to have more than just a couple vials of Alchemist Fire in the arsenal. There ought to be somebody capable of casting 3rd level arcane spells in the group by now.
Saint Trickery- The boiling makes sense to me because it likens the creature to another insect, the bombardier beetle.
Mothman- The implication of hive mind is found all throughout the text. The hive submits completely to the queen's telepathic will. The hive loses all direction and motivation should the current queen die before the new one is hatched. The queen's direct involvement in combat boosts all non-physical ability scores for that specific swarm because she can focus. Hive mind.
Andrew (I know you can't answer yet, but I'm still throwing this out there)- One of the things I'd like to see is how big a colony/hive can be. "A mile in any direction" covers a lot of ground so it'd be nice to have an idea of how often you could throw one of these swarms at a party.
One of the things I really like, as Saint Trickery notes, is the crazy mixture of many different types of insects. All the little traits that, in their individual breeds, would be a pretty easy (almost negligible) combat, make for a nasty rumble when combined into one creature with a mind for tactics and some spell casting ability. Again, it's CR 7, so it shouldn't be easy by any stretch. More than one swarm of these at a time, though... that's an ugly thought.
I'm also a fan of the creepy factor. A horde of enormous bugs closing in and TALKING? Ew. Just ew. As a horror writer, I dig it.