2. The Wirrn
The Wirrn (pronounced WIH-run, if youre interested). Their larvae from is made from bubble wrap thats been painted green, their adult form is clunky and unwieldy... and yet they still manage to be terrifying. A huge part of this is the concept. The Wirrn are insect-like creatures that travel through space looking for prey. They then reproduce by infecting other beings - the merest touch from a Wirrn larvae means that you're doomed - who gradually transform into adult Wirrn themselves, everything about who they were wiped away. This leads to excruciating pain and identity crises before the transformation is complete. Their teeth are razor sharp and if that wasnt enough, theyre also pretty much invulnerable with futuristic laser guns having next to no effect on them. To top it all off, theyre sentient. They know what is going to happen to you and can probably feel it too, as you become attached to their hive mind as you transform. They just dont care if it gets in the way of their goals. With all these advantages, its understandable why the characters see them as a such a threat. If the main characters are scared for their life, its likely that the viewers will be frightened for them - and quite probably frightened of the monsters, too. Such a strong, dark and scary concept manages to push around the dodgy effects so that even the slithering, slimy larvae become really unnerving. Its almost a shame they havent been brought back by a writer good at scary, like Moffat or Mathieson, and given a stronger design thanks to the much improved budget of the new series. Still, if you want creepy creatures posing a threat to all humanity, there are worse places to look than The Ark in Space.