What is a Species?

The question ‘what is a species?’ might sound like a simple one. We have evolved to categorise plants and animals into types, some safe like field mushrooms and other less safe like fly agaric toadstools. We have developed this idea into the concept of a species, but this is an artificial construction and there are many examples of weird creatures that to a greater or lesser degree bend the definition of a species. Our world is complex and the idea of a species is a useful one to help us understand that world, but it has limitations and it is also important to know these limits.