More data for ancient beliefs on the same topic:
Minucius Felix's Octavius: (2nd C/3rd C CE)
http://www.earlychristianwritings.com/text/octavius.html
There are some insincere and vagrant spirits degraded from their heavenly vigour by earthly stains and lusts. Now these spirits, after having lost the simplicity of their nature by being weighed down and immersed in vices, for a solace of their calamity, cease not, now that they are ruined themselves, to ruin others; and being depraved themselves, to infuse into others the error of their depravity and being themselves alienated from God, to separate others from God by the introduction of degraded superstitions. The poets know that those spirits are demons...
Thus they weigh men downwards from heaven, and call them away from the true God to material things: they disturb the life, render all men unquiet; creeping also secretly into human bodies, with subtlety, as being spirits, they feign diseases, alarm the minds, wrench about the limbs; that they may constrain men to worship them...
The same man also declared that demons were earthly, wandering, hostile to humanity. What said Plato, who believed that it was a hard thing to find out God? Does not he also, without hesitation, tell of both angels and demons? And in his Symposium also, does not he endeavour to explain the nature of demons? For he will have it to be a substance between mortal and immortal--that is, mediate between body and spirit, compounded by mingling of earthly weight and heavenly lightness...
Athenagoras's "Plea for the Christians": (around 180 CE)
http://www.earlychristianwritings.com/text/athenagoras-plea.html
Just as with men, who have freedom of choice as to both virtue and vice (for you would not either honour the good or punish the bad, unless vice and virtue were in their own power; and some are diligent in the matters entrusted to them by you, and others faithless), so is it among the angels...
These angels, then, who have fallen from heaven, and haunt the air and the earth, and are no longer able to rise to heavenly things, and the souls of the giants, which are the demons who wander about the world, perform actions similar, the one (that is, the demons) to the natures they have received, the other (that is, the angels) to the appetites they have indulged...
They who draw men to idols, then, are the aforesaid demons, who are eager for the blood of the sacrifices, and lick them...
Tatian's Address to the Greeks: (around 160 CE)
http://www.earlychristianwritings.com/text/tatian-address.html
But none of the demons possess flesh; their structure is spiritual, like that of fire or air. And only by those whom the Spirit of God dwells in and fortifies are the bodies of the demons easily seen, not at all by others,--I mean those who possess only soul; for the inferior has not the ability to apprehend the superior. On this account the nature of the demons has no place for repentance; for they are the reflection of matter and of wickedness.
The Ascension of Isaiah: (1st C/2nd C CE)
http://www.earlychristianwritings.com/text/ascension.html
Chapter 10
29. And again He descended into the firmament where dwelleth the ruler of this world, and He gave the password to those on the left, and His form was like theirs, and they did not praise Him there; but they were envying one another and fighting; for here there is a power of evil and envying about trifles.
30. And I saw when He descended and made Himself like unto the angels of the air, and He was like one of them.
31. And He gave no password; for one was plundering and doing violence to another.