Three-Armed Martian

The three-armed Martians are an unnamed sapient humanoid species with three arms who attempted to colonize Earth, only to be intercepted and possibly exterminated by three-eyed Venusians.

Biology
The three-armed Martians appear almost entirely identical to Humans, except for the presence of a third arm, located on the right side of their bodies, directly under their "normal" arm. Most other physiological differences from Humans are unknown, but due to their lack of knowledge of most of water's properties, likely due to the lack of water on Mars, it is extremely likely that they are hydrophobic, and water is definitely not a chemical solvent used by this species. Despite evolving in the Martian environment, they are perfectly capable of surviving in Earth's environment.

Culture and society
The three-armed Martians sought to colonize Earth, sending at least one advance scout to ensure Earth was ready for colonization, who held no qualms towards killing Humans to preserve his identity. In addition, they appear to have been watching Earth for long enough to know about several aspects of Earth culture, such as the corporate world, Boston, and various Human technologies. It is unknown if they wished to colonize Earth with a frontal invasion force, or by infiltrating it by disguising as Humans until there were enough of them to enact a takeover. Due to their unique physiology, their clothing, even the Earth-styled business suits their infiltrator wore, have a third sleeve for their third arm, identical to their other two sleeves. They are capable of hiding their third arms, presumably using another garment or possibly some sort of cloaking technology, in order to pass off as Humans. Due to their origin, they do not know much about water, such as what the definition of "wet" is. They appear to have had a hostile relationship with the three-eyed Venusians.

Technology
The three-armed Martians possessed a colonization fleet and smaller spacecraft capable of crossing from Earth to Mars. They also appear to have technology that can cast visual and auditory illusions, or control machines, making power fluctuate, devices randomly activate, and fake a phone call.

Appearances

 * The Twilight Zone, s02e28, "Will the Real Martian Please Stand Up?" (1961)