Idas Blue (Plebejus idas)

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2016 photographs highlighted in green. Click on any photograph to go to an enlarged picture, or simply scroll down the page.

12735_male_Isère_11Jul08 30791_male_Hautes-Alpes_7Jul12 22094_male_Hautes-Alpes_14Jul10
33323_male_Hautes-Alpes_2Jul13 32953_female_Isère_18Jun13 41351_female_Hautes-Alpes_14Jul16
13398_female_Valais, Switzerland_20Jul08 35845_female_Alpes-Maritimes_2Jul14 12968_male_Valais, Switzerland_15Jul08
12513_male_Isère_10Jul08 12733_male_Isère_11Jul08 13065_male_Valais, Switzerland_17Jul08
 
35827_female_Alpes-Maritimes_2Jul14 33327_pair_Hautes-Alpes_2Jul13  

Idas can sometimes be hard to differentiate from the Silver-studded Blue (P. argus), not to mention possible confusion with the Reverdin's Blue (P. argyrognomon) where the latter occurs. Idas is a very variable species with many subspecies across Europe, although the more lightly-marked subspecies calliopsis only occurs in France, in addition to the nominate form. The male upperside is a strong bright blue with a narrower black border than argus and wide white fringes, sometimes with uph marginal black spots or more triangular indents (see 22094) which are generally smaller than those of argus. The female upperside is brown with varying amounts of blue, with marginal lunules more prominent than argus (although this has not always been my experience) especially on the uph and there is sometimes a basal blue flush.

 

T&L shows the nominate female as being largely blue with strong uph lunules, but this also has not been my experience and I have seen a lot of idas. The unh black edging to the marginal lunules (the "studs") is usually chevron-shaped and quite sharply pointed (arrow-shaped or "sagittate") especially in s2 and s3. There are sometimes no silver centres to the marginal spots, or at least, that's how it appears - the silver is often a question of the viewing angle. Also the orange on the unf lunules does not extend to the apex as it does on argyrognomon.

In the subspecies calliopsis the male has a chequered black uph margin and reduced uns discal and post-discal spots. According to T&L, calliopsis is found in the Basses- and Hautes-Alpes between 500-1000m, although I have seen it in locations up to 1800m. Altitude ranges given in books, even the more authoritative ones, should, from my experience, be viewed only as a guide, not an absolute.

 

Another feature to differentiate idas from argus, which apparently holds true 100% of the time, is the foreleg spine. Argus has this spine, idas does not. It is not a practical way of differentiating the two species, but please see the argus page for more detailed discussion.

 
ref sex

observations

alt. m
12735 M

a dark blue male with quite heavily chequered margins, especially the uph where the border is effectively a series of heavy black triangles. I believe this of the subspecies calliopsis.

1120
30791 M a male with a rather strong blue colouring. 2020
22094 M

a male, with the typical triangular marginal markings of the nominate form.

2020
33323 M a fresh male, the uph triangular markings are very well defined. 1400
32953 F I suspect this is a female argyrognomon, although I could not discount the possibility that it is idas. There is a theory that the colour of the margins is different for the females of these two species, possibly that the idas margins are browner, but I am really not sure and my experience is inconclusive. 32953 doesn't help much, the margins apparently a little of both. The only other indicator is that idas males were not uncommon in that locality (visited over several years), but no sightings of argyrognomon males. 1120
41351 M I am fairly certain that this is idas, obviously a female, as I also had a clear view of the underside. It was also noticeably large, and in my experience female argus are nearly always smaller. 1960
13398 F

a female with only vestigial lunules on a dull dark brown ground colour. I am fairly sure this was idas even though it looks like the female argus in T&L and nothing like the idas illustration.

2200
35845 F a female, the uph markings perhaps adding weight to 32953 being idas as well. 35827 is the underside. 1400
12968 M

a male with very elongated and pointed black chevrons, for me this is 100% idas.

1700
12513 M

a male which did not look like classic idas, perhaps because it is in the shade and the white chevrons inside the unh lunules show up clearly. It was quite large and I did wonder about Zephyr Blue (Plebejus pylaon) which is a larger Plebejus although I have never knowingly seen one, but pylaon does not have silver studs and this clearly does. Idas it is, then.

1120
12733 M

a male, large and with a classic idas elongated (as opposed to argus rounded) shape, and pointed black chevrons.

1120
13065 M

a male, despite the decidedly brownish ground colour, as confirmed by the just-visible blue of the upf.

1800
35827 F a female, the underside of 35845.  
33327 PAIR a mating pair, the browner female on the right. The male unh black interiors of the lunules are not particularly sagittate, but I feel they are idas rather than argus. 1400

 

12735_male_Isère_11Jul08

 

30791_male_Hautes-Alpes_7Jul12

 

22094_male_Hautes-Alpes_14Jul10

 

33323_male_Hautes-Alpes_2Jul13

 

32953_female_Isère_18Jun13

 

41351_female_Hautes-Alpes_14Jul16

 

13398_female_Valais, Switzerland_20Jul08

 

35845_female_Alpes-Maritimes_2Jul14

 

12968_male_Valais, Switzerland_15Jul08

 

12513_male_Isère_10Jul08

 

12733_male_Isère_11Jul08

 

13065_male_Valais, Switzerland_17Jul08

 

35827_female_Alpes-Maritimes_2Jul14

 

33327_pair_Hautes-Alpes_2Jul13