"The Gorgonian plain of Cisthene, where
The Phorkides live, those three long-lived
Young women in the shape of swans, who share one eye
And one tooth – the sun never looks at them
With his beams, nor the moon at night.
Near them are their sisters, the three winged
Snaky-haired Gorgons hateful to humans, Whom no mortal can look upon and live.
That’s the kind of thing you should guard against. But let me tell you about another difficult-to-handle sight:
Watch out for Zeus’s sharp-beaked unbarking
Dogs, the gryphons, and the one-eyed army
Of Arimaspians on horseback -- they live
Around the gold-flowing water of Pluto’s stream.
Keep away from them. Then you’ll come to a far
Country, and a black tribe who live near
The springs of the sun" -Prometheus Bound
Yeah, ok, then why does Prometheus have to explicitly warn Io (the woman who's basically just what people WANT medusa to be) to avoid them? He clearly has them being dangerous and to be avoided, putting them together with natural dangers and griffins.