Was Ungoliant more powerful than Morgoth?

Question

Ungoliant and Morgoth formed an alliance temporarily and came to Valinor, while Morgoth cast a dark shadow covering them, Ungoliant sucked the light from the Two Trees and darkened Aman, hence why it fell back into darkness. Meanwhile Morgoth and Ungoliant made their escape across the Helcaraxe, once they returned to Middle Earth Ungoliant demanded the silmarils from Morgoth. When he refused, Ungoliant is said to have wrapped him in her webs and he wasn't able to break free until his Balrogs arrived and attacked her and she fled South.

So based on this information about Ungoliant, even though she is a Maia, was she more powerful than Morgoth?

Answer 1

At the moment of their confrontation, obviously yes. In general, perhaps not; there were some extenuating circumstances at the time:

But Ungoliant had grown great, and he less by the power that had gone out of him

^{The Silmarillion III Quenta Silmarillion Chapter 9: "Of the Flight of the Noldor"}

Ungoliant has been gorging herself on the magic sap of the Trees of Valinor, which has temporarily buffed her strength. Note how she's described while in the process of drinking the Light of the Trees (emphasis mine):

Ungoliant sucked it up, and going then from Tree to Tree she set her black beak to their wounds, till they were drained; and the poison of Death that was in her went into their tissues and withered them, root, branch, and leaf; and they died. And still she thirsted, and going to the Wells of Varda she drank them dry; but Ungoliant belched forth black vapours as she drank, and swelled to a shape so vast and hideous that Melkor was afraid.

^{The Silmarillion III Quenta Silmarillion Chapter 8: "Of the Darkening of Valinor"}

Melkor, in contrast, has put a lot of his power outside himself in the course of his mischief-making, so he's not really at full capacity. This process, incidentally, is what eventually makes him vulnerable and leads to his defeat at the end of the First Age.

Unfortunately, we have very little definitive idea about what, exactly, Ungoliant is, or how some of the things she might be fit into the Middle-earth power structure. With that limitation in mind, it becomes impossible to definitively state which of Ungoliant or Morgoth would have been more powerful in a standard situation.

Answer 2

We don't know whether Ungoliant was a Maia or some other kind of being. Just like Tom Bombadil, she was left an enigma by Tolkien. Tolkien's early version of the legends (The Book of Lost Tales) calls her a primeval spirit, believed to be a creature bred of the darkness of the Void. It is possible that she was a physical manifestation of darkness rather than one of the Ainur. http://tolkiengateway.net/wiki/Ungoliant

Thus, I count her as at least equal, if not superior, in strength to Morgoth.

Answer 3

Ungoliant was basically a result of the evil made in the songs of the Ainur by Melkor. So originally Morgoth was stronger than her. But after drinking the light and power of the Two Trees, she became a match for Morgoth.