The Davannans are a humanoid species wich developed an advanced emotionless civilisation with space faring capacities which, as of the 1950ies, was dying from the aftermath of a devastating nuclear war of their homeworld combined with an epidemix which caused their blood to evaporate.
The look very similar to humand but with white pupil-less eyes. They are telepathic and, focussing their eyes on a subject, capable of hypnosis and even killing by destroying the optic and nervous tissues of the victim.They feed on a black liquid containing all the nutrients they need. They are very sensible to loud sounds, which can be very painful to them.
In 1957, they sent a scoutto study the effects of Human blood in their own biology, but after they lost contact with him, they decided not to go on any further with potential invasion plans. A fact they never knew, their scout had in fact died in a car accident.
The alien had brought with him a non-sentient creature from his home planet, which resssembles a mix between an octopus and a flying umbrella and which could attack people by jumping at their head and covering it with its surface.
Source: Not of this Earth, 1957. Directed and produced by Roger Corman, written by Charles B. Griffith and Mark Hanna.