Silver-studded Blue (Plebejus argus)
2009 photos highlighted in yellow. Click on any photo to go to an enlarged picture, or simply scroll down the page.
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| 11088_male_Bouches du Rhone_4Jun08 | 12058_male_Alpes de Haute Provence_6Jul08 | 16872_male_Alpes Maritimes_27Jun09 |
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| 16859_male_Alpes Maritimes_27Jun09 | 11087_male_Bouches du Rhone_4Jun08 | 12051_female_Alpes de Haute Provence_6Jul08 |
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| 11138_female_Bouches du Rhone_4Jun08 | 13639_female_Lozere_21Aug08 | 13647_female_Lozere_21Aug08 |
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| 2756_female_Italy_16Jul06 | enlargement of 2756 showing middle leg spine - argus | enlargement of 3364 - idas |
Common in most of France, sometimes occurring in thousands, but can be difficult to differentiate from the Idas Blue (P. idas). The argus upperside usually has a broader black border (clear in 12058) than idas, often with marginal black uph spots. My feeling is that the unh black interiors to the marginal lunules are quite pointed for idas and more rounded for argus. However, the Lafranchis ID book describes both argus and idas as "sagittate". It also says that the argus unf spots are more arched, having a "?" shape, than idas - this is clear in 13647. In my experience, argus is fairly consistent in terms of size and noticeably smaller than idas, but this would only be a guide at best - the Lafranchis France book gives the argus wingspan at 10-16mm and idas 11-16mm. Argus also seems more rounded, whereas idas seems to me to be more angular.
Argus has a small spine on the foreleg tibia (see above) but you need to be very close to see it, or have a digital camera with high resolution. Idas has a minute spine, clearly too small to be confused with an argus spine. However, this ID pointer as described by the leading books (see the introductory page) originally did not seem to add up (but see below):
1) does it occur on the male only? T&L, Lafranchis France, Lafranchis ID and H&R all say "male". The enlargement of 2756 - which is clearly a female (from the brown ground colour and the apparent curvature of the body shape) - shows a very strong spine on the mid-leg. Are the books wrong? In many respects, T&L is very much a straight lift from H&R, so if H&R got it wrong, T&L would probably follow. My feeling is that it occurs on both sexes, as I have studied many photos of females that appear to have the same strong spine.
2) which leg does it occur on? They have three pairs of legs. It always seems to be on the middle leg. Is this what the books mean by foreleg?
3) which way is it pointing? In all of these photos, and many more that I have studied, the spine is clearly and consistently pointing backwards, but in H&R and Lafranchis ID the illustrations show it pointing forward.
4) several authors refer to it as a "hook". It doesn't look like a hook to me.
However, after further study prompted by debate on the UK Butterflies website, it became clear that the books were not referring to the midleg spine. This is a relief because there are photos on the idas page that also have this midleg spine but are clearly (in my opinion) idas. I then looked at an expanded photo (here) showing the argus legs and discovered a backward-pointing hook on the foreleg tibia, as indicated by the blue line; however, this is not the spine in question (but it might explain why it has been referred to as a hook - maybe they were looking at the wrong "spine", too). The actual spine in question may just be visible on this expanded photo, thin and black and laying parallel to the leg, but I am not 100% certain of this.
If the spine is this obscure i.e. barely visible even using cameras with powerful macro lenses, it is not of much value in a field guide. It is really only of value if the specimen is caught and examined under a microscope or strong lens, in much the same way as the genitalia. My views on this are that only accredited scientists and entomologists who NEED to know the ID should be catching and examining specimens in a way that may cause distress if not death. I exclude netting, examining and releasing which, if done with care, does not cause distress.
11088: a very light border for male argus. Where the uph border is light, it tends to break up into black spots rather than a smooth border. Altitude 35m.
12058: a more typical broad male argus border. Altitude 1550m.
16872: a typical male, strong blue colour, wide dark upf border and the uph border breaking up into discrete round marginal spots. Altitude 900m.
16859: a typical male underside, pale silvery-grey ground colour and rounded black edging to the unh orange lunules. Altitude 900m.
11087: a typical male underside. The black interiors to the unh lunules do not appear sagittate to me (see comment above). Altitude 35m.
12051: a very lightly marked female, with a narrow forewing. Altitude 1550m.
11138: a well-marked female, with strong arched orange lunules on both wings and a spattering of blue scales on the uph. Altitude 35m.
13639: a less well-marked female with rather indistinct and faint orange lunules on the upf. Altitude 1200m.
13647: a strongly-marked female underside, with good arching of the unf post-discal spots. The strong brown ground colour sets off the white areas inside the unh lunules. Altitude 1200m.
2756: a female with the middle leg spine clearly visible in the blow-up shot. The silver studs are quite thin. Other shots of males show exactly the same spine. Altitude 990m.
11088_male_Bouches du Rhone_4Jun08
12058_male_Alpes de Haute Provence_6Jul08
16872_male_Alpes Maritimes_27Jun09
16859_male_Alpes Maritimes_27Jun09
11087_male_Bouches du Rhone_4Jun08
12051_female_Alpes de Haute Provence_6Jul08
11138_female_Bouches du Rhone_4Jun08
