Myrmarch

(From 3.5e Monster Manual I - 2003):

Formians hail from the plane of Mechanus. They seek to colonize all that they see and incorporate all living things into their hive as workers. 

Expansionist in the extreme, formians are dedicated to spreading their colonies until they have taken over everything and their order is unquestioned. To further this end, they attack all other creatures, usually to put them to work building and expanding cities. Formians maintain these “conscripted” workers as well as those mentally dominated by the power of their taskmasters. 

A formian resembles a cross between an ant and a centaur. All formians are covered in a brownish-red carapace; size and appearance differs for each variety.

Formians build fabulous hive-cities in which hundreds of the creatures dwell. They are born into their station, with no ability to progress. Workers obey orders given by warriors, myrmarchs, or the queen. Warriors carry out the will of their myrmarch commanders or the queen. Myrmarchs take orders only from the queen herself, although they have different ranks depending on services rendered. These are not positions of power but of prestige. The most prestigious of the myrmarchs guard the queen. Taskmasters are equal in rank to warriors but seldom interact with other formians.

The Myrmarch: Myrmarchs are the elite of formian society. Much more than those beneath them, these creatures are individuals, with goals, desires, and creative thought. Very rarely do these thoughts conflict with the wishes of the queen, though—most myrmarchs are still very loyal to her. 

Myrmarchs are commanders in formian armies and leaders in formian communities. They are the hands of the queen, carrying out her direct orders and making sure everything goes as she desires. Myrmarchs also have a secondary role: stamping out chaos wherever and whenever they can. Those who foment disorder, and particularly creatures that revere or exemplify it (such as slaadi), are the hated foes of myrmarchs. 

A myrmarch is about is about 7 feet long and about 5-1/2 feet high at the front. It weighs about 1,500 pounds. Its claws are capable of fine manipulation, like human hands. Each myrmarch wears a bronze helm to signify its position (the more elaborate the helm, the more prestigious the position). 

Myrmarchs speak Formian and Common.

Combat: Myrmarchs’ claws are like hands and thus serve no combat purpose. Myrmarchs occasionally employ javelins for ranged attacks, coated with poison from their own stingers. 

They fight intelligently, aiding those under them (if any such are present) and commanding them through the hive mind. If chaotic creatures are present, however, a myrmarch is singleminded in its quest to destroy them. 

A formian myrmarch’s natural weapons, as well as any weapons it wields, are treated as lawful-aligned for the purpose of overcoming damage reduction. 

Poison (Ex): Injury, Fortitude DC 20, initial and secondary damage 2d6 Dex. The save DC is Constitution-based. 

Spell-Like Abilities: At will—charm monster (DC 17), clairaudience/clairvoyance, detect chaos, detect thoughts (DC 15), magic circle against chaos, greater teleport; 1/day—dictum (DC 20), order’s wrath (DC 17). Caster level 12th. The save DCs are Charisma-based.

(From Planescape: Planes of Law Monstrous Supplement - 1995):

"Had mine eyes ever beheld such beauty? To think, all fashioned by a bug!"

- Unknown traveler upon reaching a formian city

Native to Arcadia, formians are also called centaur ants. As their moniker indicates, they appear to he uprightwalking ants, but their sentience is that of warmblooded creatures as opposed to insects. They’ve always inhabited Arcadia, and sages say they always will. Though formians found on the Prime make war on each other, Arcadian formians of different hives have learned to live together peaceably. 

Similar to true ants, there are three basic types of formians: the worker, the wamor, and the myrmarch. (A fourth type, the queen, is extremely rare.) Unlike ants, formians’ waists are flexible; thus, they often move with only four legs, their heads and thoraces raised. Their forelegs are jointed at the wrist and have three opposing claws, which they can use to manipulate objects and to attack. Formians come in various subdued colors, which serve no function other than to indicate their cities of  origin.

Formians of warrior level and higher can communicate with humans, though their version of common sounds more like eerie chittering. They communicate with one another in their own speech, which is incomprehensible to most other beings.

The Myrmarch: The myrmarch is the size of a horse. Its claws are capable of finer manipulation than that of human hands.

Combat: Myrmarches attack with their mandibles and a poisoned sting. The poison causes 3d12 points of damage and paralyzes opponents for 1d4 turns (save versus poison to take half damage and avoid paralyzation).