1 Ishmael: Just the three of you?! I thought you were the advance scouting party! You mean you're the entire invasion fleet?!
2 Martian 1: Allow me a moment to confer with my colleagues... {steps aside to discuss with the other Martians}
3 Martian 2: {in huddle} I suggest we need to exaggerate our forces, to keep him off guard.
3 Martian 1: {in huddle} I concur.
4 Martian 1: {to Ishmael} Did I say just three of us? Ho ho ho! No, of course not. Don't be ridiculous. There are three more on their way as we speak.

It's not clear whether these three are just the only Martians trying to invade Earth, or if these three are in fact the entirity of the Martian race. We've never seen any others, or had anything that implied the existence of more of them.

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2017-07-23 Rerun commentary: It's now been established in the canon that these three are in fact the last three Martians in existence.

It definitely makes it easier for me that way, since I don't have any other Martian minifigures.

Readers may imagine I have loads and loads of Lego bricks and figures, but in reality you could probably fit all of the Lego parts that I own into a box... hmmm... about the size of a dishwasher.

Okay, okay, to most people that is loads and loads of Lego bricks...