'Lets Make A List Of All Of The Creatures On Earth',

it sounds easy,

just cobble together a number of different lists already in existence, but as most things, it is not that easy, some lists may not cover some species, while some may not follow some principles set by scientists, amazingly after all of the work by scientists, researchers and taxonomists over the past few hundred years, currently there is no agreed-upon list of species available, as ScienceAlert details:

"Listing all species may sound routine, but is a difficult and complex task," says environmental scientist Stephen Garnett from Charles Darwin University in Australia. "Currently no single, agreed list of species is available." 

also worthy of note is this from plant biologist Kevin Thiele at the Australian Academy of Science,

"Importantly, [the plan] clearly defines the roles of taxonomists – the scientists who discover, name, and classify species – and stakeholders such as conservationists and government and international agencies, while taxonomists would have the final say on how to recognise and name species, the process ensures that stakeholders' needs are considered when deciding between differing taxonomic opinions."

out of interest I took the photograph of the owl when we were with Steve and Kai in Edinburgh in March 2018, and there was me thinking that all you had to do was grab a few lists from the likes of Aristotle, Carolus Linnaeus, Andrea Cesalpino, and a few other taxonomists, but apparently it is not that simple.