Our Association has members with extensive experience in Species identification.
It takes specialized skills and scientific expertise to correctly identify species. There are millions of species on Earth—between 5 and 30 million —and just 2 million species have been identified and named. That means there are more species that are unknown than known. In addition, some species are so similar that differences are visible only through DNA analysis. National Geographic.com
One of the challenges of getting close to nature is working out how to identify species of plants, animals, insects, reptiles ......... This may help to clarify that whilst we all try to be exact about it, there is sometimes room for some discussion on its accuracy. Check out lifeonterra.com for a video about The Species Problem.
When someone says it better than you can then its best to refer you to them. The Guardian.com has a good description of species identification issues in its article How species are identified where is states:
The real question of course though is how can species be recognised and identified? This is where things get complex and disagreements can arise between biologists, since species are more fluid than elements or atoms. By definition, species evolve and over time populations change, diverge and lineages split into new species.