If the party has made it this far by violence, they will have to track the Myrmarch down (DC 15) and engage in a great deal of violence along the way. They will be able to release human hostages of varying ability (some with healing powers, some not). The Myrmarch will be ready for them (the advantage of being in a hive mind) and will order the party to "cease their unlawful activity" before attacking.
If the party gets this far by negotiation/bluffing the Myrmarch will explain that this land was ceded to the Formians 75 years ago and it is theirs by right of law. The Myrmarch will have more attendants around her (as she did not have to send them into battle) but she will be prepared for for the party.
In other words, the party can have lots of little fights to get to the Myrmarch, or brace themselves for one big one.
If the party has gotten there by non-violent means the Myrmarch will ask if the human lands want to re-negotiate the contract. If the party agrees, they will have 48 hours to get an official representitive or proof that they are the legal respresentives of the land (easy enough to get, the local rulers are out of their league on this one) or just lie about it (Bluff DC modifier +15, and the Myrmarch is unfriendly).
If the encounter degenerates into combat the Myrmarch will attempt to teleport to her queen if reduced below 40 hit points.
next: Queen formian and conclusion!