Silmarillion - Valaquenta "Of the Enemies": Yet so great was the power of [Melkor's] uprising that in
ages forgotten he contended with
Manwe and all the
Valar, and through long years in
Arda held dominion over most of the lands of the EArth. But he was not alone. For of the
Maiar many were drawn to his splendour in the days of his greatness, and remained in that allegiance down into his darkness; and others he corrupted afterwards to his service with lies and treacherous gifts. Dreadful among these
spirits were the
Valaraukar, the scourges of fire that in
Middle-earth were called the
Balrogs, demons of terror.
Flammifer quoted:
"Far, far below the deepest delvings of the Dwarves, the world is gnawed by nameless things. Even Sauron knows them not. They are older than he."
Sauron was among the "others he corrupted afterwards", being first a
Maia of
Aule. So if
Ungoliant fits into the 'nameless things' category then she was older than he, and herein lies a problem, because the
Ainur sang the song through which Illuvatar created the world, and the Maiar are of the Ainur. It can be overcome by assuming that age, in terms of time, was invalid in the heavenlies, which were outside of time; so Sauron's age only began to be calculated when he entered Middle Earth.
This means that, if
Gandalf was right, Ungoliant was already there before Sauron, so she was one of the first to be drawn to
Melkor, ie: a Maia (though an ugly one).
Shelob was her 'daughter' - a lesser spawn of spontaneous gestation, or product of a mating with some lesser arachnid maybe, but not a deity like her mother - she seems to lack the
evil intelligence of Ungoliant, having only hate for every living thing and an appetite to consume all she hated. Corruption can only multiply in degenerate form, and Shelob was a degenerate form of her powerful mother, though still a force to be reckoned with.
Thingol and
Melian's union produced children who were not Maiar but
Elves (though of greater power). If Ungoliant mated with a natural arachnid, then I would call her offspring a spider, though a great one, and infused with her mother's evil and just enough sentience to use it.