www.ukbutterflies.co.uk

For many years, the Northern Brown Argus was considered to be a subspecies of the Brown Argus. However, it is now believed that this is a distinct species in its own right and has a different flight time and different number of broods - this species being single-brooded.

So on that basis, Northern Common Blues should be considered a separate species. They are certainly single brooded here on Mull, but universally thought to be the same species. They certainly look like their southern cousins. (recent picture on Mull)
Bear in mind that many Northern Brown Argus individuals lack white spots on the forewings. Equally many [Southern] Brown Argus do have white spots (current research by David Newland)

Jack

Jack Harrison wrote:So on that basis, Northern Common Blues should be considered a separate species.

Hi Jack - what it doesn't say is "... it is now believed that this is a distinct species in its own right BECAUSE it has a different flight time and different number of broods". I believe that DNA analysis has provided conclusive evidence of these being separate species, not just morphological and phenology differences.

Cheers,

- Pete

I accept that I misunderstand. I might not have made that mistake had it said:

"However, it is now believed that this is a distinct species in its own right and as it happens, has a different flight time and different number of broods......".

But no big deal. I'm sure my Northern Common Blues had a day off today - rain, rain, rain until late afternoon when there was a welcome and accurately forecast clearance. Maybe the Blues will be off an evening jaunt right now as I write.

Jack

You raised an interesting point, Jack, that has a bearing on the history of taxonomy. It took a long time for the early classifiers to determine which characteristics were 'significant' in deciding where to place species boundaries. In general they found that colour and behaviour were very poor classifiers. On that basis, where would one place brightly coloured day-flying moths, for example?

They decided that structural features were the key. So, for example, all moths have a 'frenulum', coupling the fore and hind wings, whereas butterflies do not. Of course, there is always some critter that doesn't want to play and I believe that there is one species of Australian Skipper that does have a frenulum! At least this seems to demonstrate that Skippers really do lie on the borderline between moths and butterflies.

Differences in genitalia are often a decisive boundary; obviously, if two species cannot mate, they are forced to remain separate!

The significance of DNA analysis is that it takes the analysis of 'structure' down to the molecular level. This type of analysis is causing havoc in plant classification - several orchids have had to be re-classified, for example, after examining their DNA.

I've no idea how all this applies to Blues and Arguses (Argi?) but something, possibly at the molecular level, will be a deciding factor. We can never be sure that the animal itself is aware of that, since all taxonomy is purely man-made.

Mike