The Macra (Doctor Who: Series Three)

First Appearance: (Original Series) Doctor Who: Episode: "The Moonbase Episode Four"

First Appearance: (New Series) Doctor Who: Series Three: Episode Four: “Gridlock”

 The Macra had devolved from a race capable of building it's own empire into a mindless, giant crustacean that fed off poisonous gasses (possibly even people). One colony of the Macra survived on the planet New Earth, where they found there way into the Motor Way and bred, using the fumes from the car exhaust and some of the people travelling on the “Fast-Lane” as food for survival.

“Gridlock”

The Macra attack and destroy a car (car-1015) that was illegally travelling in the fast-lane, taking advantage of the fact that the steering wheel was locked (due to the three adult minimum as a car-share policy for New New York's Motor way). The couple driving the car where killed.

They later crush another car that is travelling behind Car-434 diamond 6, which is being driven by a cat-kind called Javit. Just before her death and the death of her other two passengers, she warns Martha, Milo and Cheen to drive and escape before they too die.

Later when the Doctor reaches the final layer of the Motor Way traffic before the “Fast Lane” begins, he hears the Macra beneath him. Unable to discover what the noise is from the rather startled business man (who owns the car) and questioning what the “lights were” (the Macra's eye-stalks), he uses the main console of the car and the sonic screwdriver to activate the ventilation system below, recognising the shapes and form of the hundreds of creatures below to be “The Macra” as the gas slightly began to clear.

After failing to get access to the main Motor Way, Martha tells Milo to turn off everything in the car hoping that it would stop the Macra from detecting them and trying to claw at them with their pincers. Despite protests Milo does and the attack stops immediately.

The Doctor explains that the Macra “used to be the Scourge of this Galaxy” feeding off polluted gas and created/ ran a “small empire” that was driven by the enslavement of humanity to mine gas for them. When the business man states that they don't look capable of building empires, the Doctor states that the billions of years between the fall of the Macra empire and the current time he was in now (5,000,000,053) had led them to devolve into mindless “beasts.”

The Doctor tries to argue with Novice Hame (who has followed him through the cars) that they can go down and that the Macra are a dangerous threat to everyone, but she teleports him away claiming that the situation is far worse than he knows.

After deciding to turn the engines back on and continue driving The Macra continue their assault on the car, while Milo tried to steer through the swarm of pincers. One of the Macra successfully grabs the car and starts compressing it, but the car gets away when another Macra slams it's claw into the first.

The Macra were left alone after the Motor Way was finally opened and all the drivers escape, losing both their food sources.