General Information
Director: Don Richardson
Writer: Robert Hamner
Cast: Guy Williams, June Lockhart, Mark Goddard, Marta Kristen, Billy Mumy, Angela Cartwright, Jonathan Harris, Ronald Gans, Lyle Waggoner, and Ralph Lee
Composer: None (Stock Music)
Air Date: 11/22/1967
Production #: 1504
Overview
Having pursued a female robot to the Zeta star system, Alien Leader (Ronald Gans) and his mechanical men (Lyle Waggoner and Ralph Lee) seek assistance from the
Robinson family. Complications arise when the Robot B-9, now madly in love with the female robot, decides to harbor his romantic interest from the authorities.
“Deadliest of the Species” benefits from an action-packed and relatively serious, if not completely camp-free, execution. That being said, the Robot’s betrayal will likely offend Lost in Space fans for obvious reasons.
Pros
While approaching the wreckage of a space vessel, the Robot utters his catchphrase (i.e., “Danger, Will Robinson! Danger!”) for the first and only time in the entire series.
Additionally worth noting, the authoritative demeanor of Ronald Gans’ character (identified as “Alien Leader” in the closing credits) should allow viewers to accept him as a no-nonsense law enforcement officer in spite of his silly appearance.
Cons
Similar to “War of the Robots” from season one, “Deadliest of the Species” attempts to humanize the Robot B-9 so that the audience can easily relate with him. 
Nevertheless, the Robot’s anthropomorphic qualities are overplayed to the point of absurdity in this offering. At one point, for example, the Robot erupts into a crying fit after enduring a barrage of Dr. Smith’s alliterative insults. Also cringe-worthy, the Robot falls in “love” with an alluring but dangerous “female” counterpart—a nonsensical character transition that fails from both a logical and an emotional standpoint.
Analysis
Upon forming a relationship with the female robot, the Robot B-9 places the Robinson family in grave danger simply to protect his new companion. Despite serving as a commentary on how certain men will sacrifice everything in order to accommodate a charming or attractive woman, Robert Hamner’s narrative deserves criticism for depicting the Robot—normally a likable, self-sacrificing character—in a negative and disloyal manner.
Concluding Comments
The final Lost in Space episode to feature Ronald Gans (known for his portrayal of the Frog Alien in “The Golden Man”), “Deadliest of the Species” is marred by the Robot’s sudden and inexplicable change of personality. For this reason among others, science fiction enthusiasts should look elsewhere for a captivating robot-themed story.
Overall Quality: 4/10
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This is my number twenty ranked episode for the psychedelic and far out, all over the place, highly inconsistent and relatively overrated, shortest final colored season..
Where was Maureen during this episode?
Maureen does appear, but I think only in one scene aboard the spaceship.
Here we go. Being only the fourth episode produced and filmed on the season does not mean it is good. Hardly anything can save this one from being one of my bottom four or five episodes of the entire series, and they all come during this season for me.
This one is just a ridiculous and embarrassing idea. Trying to save it with a lot of action and ‘thrilling’ sequences does not work. As a youngster I thought this one was ‘okay.’ Nowadays I just see it for what it is worth..not much..
I once wrote a review on this one, and it was not pretty.. :-/
She shoots the robot with a ray before he portrays the family. Perhaps the ray messed up his programing and turned him against the Robinsons.