Male on sainfoin (the larval foodplant), Switzerland, June 2005
The same male
Male, June 2006, Switzerland
This picture was taken two days after the above one, at the
same site. I think it is the same butterfly...
Brown female on foodplant, sainfoin, Switzerland, April 2011
Male on sainfoin
Female, Switzerland, June 2005
Same female
Same female
Another shot of the same butterfly!
Distribution - very sporadic in eastern part of range
Osiris blues are relatively uncommon butterflies, found from
West
Switzerland through to North Spain and Italy, and also more
widely but sparsely further east. They fly in grassy meadows where the
foodplant, sainfoin, grows, often on south-facing slopes or by the side
of roads. I see them regularly at the same sites, usually in ones and
twos, rather than great congregations like so many blues. Males readily
come to minerals and dung, females less. These are more often to be
seen on or near the foodplant.
Males are easy to identify. The upperside is a deep, matt blue, neatly
bordered with a narrow, black line. The underside is a bright, slightly
bluish white. Care should be taken with male Provençal short-tailed
blues, which may almost completely lack a tail and look superficially
similar, but these have brighter uppersides and at least a kink in the
hindwing margin. Worn individuals might also be mistaken for mazarine
blue. This latter has broader upperside margins, less bright white
undersides, and critically, the upper two spots in the post-discal
series on the underwing hindwing point outwards, towards the outer
margin, making a broadly oblique angle with the third. In Osiris blue
these two spots are perpendicular to the wing edge, or even point
slightly inwards, usually making a right angle with the next spot (if
this angle is oblique, it is because of the position of the third
spot). Females are very similar to little blues. Usually, but not
always, there is some blue in the basal regions of the wings -
sometimes a great deal, as in the last female illustrated above. Female
little blues are completely brown. Osiris blues are also typically
larger, but alpine populations of little blue can be large too.
Osiris blues are said to be bivoltine, flying in April-June and then
July-September. In Switzerland I have only seen a single brood. This
flies well into July at altitude but is usually over by mid-June in the
valley. I suspect the species is bivoltine only in the more southerly
parts of its range. It overwinters as a larva, entering diapause early
where it is single-brooded. Various species of sainfoin are taken as
foodplant.
