D&D 5E Help putting stats on giant sentient cockroaches

[Lanliss]

For those who don't know, Suzzanne Collins, the author of the recently famous Hunger Games trilogy, had a series of books before called the Underland Chronicles. It is a massive underground continent, not dissimilar from the Underdark, sans rampant insanity. It was full of giant, sentient animals, who banded together in various factions, mainly fighting for or against the humans who lived there.

Now that you have the basic back story, I would like to build this as a continent in my world that I am building. Does anyone have any experience giving stats to giant sentient bats? Not planning on having any caster enemies, as they were all a bit busy surviving the pitch black terror of the Underland to try worshipping a god or gods, so any help on how martial enemies can handle casters would be helpful too.

EDIT: I just realized that an actual list of animals might be helpful, so here it is.

Rats: average anywhere from 4 to 9 feet
Bats: mostly over 6 feet, big enough to carry a pair of rats, or more if needed.
Roaches: only about 1 to 2 feet off the ground, but probably around 5 feet long.
Spiders: too spread out to say. None smaller than a 3 foot leg span, some up to 10 foot I think.
Mice: probably about 2 to 3 feet tall, and 3 to 4 long, not counting the tail.
Firefly: around 3 feet from tip to antenna. will mostly be npcs, as they dislike fighting, being an entire species too lazy to do anything. Kept alive for their massive usefulness as lights.

That is all I can think of for now.

 

[Jediking]

You can just treat them as any other group of intelligent, sentient creatures. Using the stat block of a Giant Bat (or even larger birds) could be a good start, and then add in a trait or ability that fits within your lore/how their society is. Bats might be able to strike in complete darkness, Rats might be able to spread disease, Spiders can set traps. If they know they can't survive a direct Fireball, they will take steps to avoid ever having the caster see them.

If you don't want actual learned casters, maybe innate spell-casting is the easiest way to go. A Firefly race may have some innate magical control over their own heat and be able to cast something similar to Burning Hands. Of course, if you want to ditch magic altogether refer back to the race's culture and how they survived until now anyways. Maybe they harvest plants or herbs that have effects that can replicate spell effects (like a poisonous mushroom that causes paralysis), or they built spike traps right next to a flammable gas vent. Hobgoblins may not have a caster with them, but if they corner the sorcerer and have archers pin him down it may not end well.