The beings named Frogs by the humans of the 3rd millenium. are a sentient humanoid species which has developed an advanced space faring civilisation whose behaviour seems antagonistic to the humanity of the time. They appear as blurry sparkling humanoid shapes. It remains unknown if this is their true appearance or if this is due something shielding them. As such, they appear immune to beam weapons but exposition of oxygen is toxic to them.
Source: Tv series Raumpatrouille – Die phantastischen Abenteuer des Raumschiffes Orion (literal translation: Space Patrol – The Fantastic Adventures of the Spaceship Orion), also known as Raumpatrouille Orion, and Space Patrol Orion in English.