Formians are strangely reminiscent of ants, except that they're man-sized and have humanoid limbs. Lore states that they originate in another plane, but what suffices to most adventurers is that where there's one, there's a hiveful, and they all are of one mind regarding intruders. The workers may not appear so bad, but they're always guarded by warriors with fighting skills and myrmarchs that wield magic in addition to hitting hard.
All formians are naturally resistent to physical and cold damage thanks to their hard, protective carapaces. They are also immune to poison and sneak attack. As if this wasn't enough, the soldiers and myrmarchs are resistant to magic and the latter also regenerate. Do not underestimate their intelligence and spot checks just because they look like bugs! All of them are clever, and their queen is said to see true.