Very cool atmosphere. I especially like how the damage sound, combined with the attack rate on the bigger ants, makes it sound like a heartbeat. That fits well with the eerie music.
If I'm understanding correctly, you can feed an ant to a mouth to get an upgrade? I found it very hard to feed it the right ant. I ended up losing all my upgraded guys that way...
Are there health pickups hidden in the walls, or do you just heal in certain corridors?