The TV series Alien:Earth has introduced a number of new creatures to the much loved, albeit terrifying, Alien franchise.

But how realistic are the new aliens? That’s a question that we – a trio of scientists who are also great fans of the franchise and show – have tried to tackle with a ranking. To be clear, we are not trying to find flaws in the show. Like many fans we are simply having fun using science to analyse the creatures.

All species in the series draw inspiration from real living organisms and processes seen on Earth, but crank it up to the extreme. We therefore won’t explore all those parallels, but instead focus on how plausible the organisms are in terms of underlying processes such as physics, chemistry, metabolism and evolution.

Our most plausible creature is the large blood-sucking tick. On Earth, the deer tick Ixodes do swell to the size of a walnut when feeding, which is not too different from the Alien:Earth tick. In the show, we see it attack the jugular and quickly take on a couple of pints of blood.

The perhaps surprisingly quick death of the unfortunate prey most likely results from hemorrhagic shock due to how quickly the blood is lost. It is possible that some sort of chemical agent (perhaps an anticoagulant, as has repeatedly evolved in blood predators on Earth) is also injected. We do see a defence mechanism in episode five where the ticks release an airborne toxin to prevent them being removed from their host. Chemical defences like poisons and venom are common in animals and plants on Earth to deter predators.

In later episodes, we see it break containment (with the help of another alien) but we’ll assume it is simply seeking a body of water to lay its tadpoles in, rather than exhibiting intelligence. Horrifically, we see nothing that completely prohibits a life form like this.

This creature, which as discovered and named in the show by the crew of the........

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