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 analyze 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.

1. The tick

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 defense mechanism in episode five where the ticks release an airborne toxin to prevent them being removed from their host. Chemical defenses like poisons and venom are common in animals and plants on Earth to deter predators.