Actually they are part of the organized militia. However the parties to a contract cannot define the terms of the contract *after* the contract is written, thus the term "militia" means what it meant September 25, 1789 when the First Congress passed the Bill of Rights to be sent to the sates, and until December 15, 1791 when they were declared ratified. However the the Militia Act of 1972 does tell us what Congress thought the militia was. The states may have, and in fact *do* have different definitions. Texas defines it thusly:
Title 4 § 431.001. DEFINITIONS. In this chapter:
(1) "Reserve militia" means the persons liable to serve, but not serving, in the state military forces.
(2) "State militia" means the state military forces and the reserve militia.
(3) "State military forces" means the Texas National Guard, the Texas State Guard, and any other active militia or military force organized under state law.
(4) "Texas National Guard" means the Texas Army National Guard and the Texas Air National Guard.
§ 431.081. PERSONS SUBJECT TO MILITARY DUTY; PERSONS NOT ELIGIBLE TO ENLIST.
(a) A person is subject to military duty if the person is:
(2) a citizen or a person of foreign birth who has declared an intent to become a citizen;
(3) a resident of the state;
(4) at least 18 and not more than 60 years of age; and
(5) not exempt under Subsection (b) or (c) or United States law.
However all that really doesn't matter, the Constitution says "the right of the people not right or power of the militia, or power of the states. Militia service is a duty, not a right, keeping and bearing arms *is* a right, a right of the people. Texas' state constitution terms it a right of the citizen and they aren't protecting their own militia against being disarmed by itself.
Every citizen shall have the right to keep and bear arms in the lawful defense of himself or the State;...".
I was quoting current Federal Code, which superceeds Texas law with respect to the Federal militia.