Iolas Blue
Iolana iolas

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Iolana iolas

Male, Switzerland, June 2014

Iolana iolas

Male, Switzerland, May 2018

Iolana iolas

Male, Switzerland, May 2018

Iolana iolas

Male, Switzerland, May 2016

Iolana iolas

Male, Switzerland, May 2016

Iolana iolas

Female, Switzerland, May 2017

Iolana iolas
Female, Switzerland, May 2017

Male, Switzerland, May 2006

Male, Switzerland, May 2008

Male, Switzerland, May 2006

The habitat - a bladder senna bush

Female, Switzerland, May 2007

There is a video of this female laying eggs HERE

Female, Switzerland, May 2007

Female, Switzerland, May 2007

Female laying in the calyx of bladder senna, Switzerland, May 2007

Female laying in the calyx of bladder senna, Switzerland, May 2007

Male, Switzerland, May 2005

Male, Switzerland, May 2005

Male, Switzerland, May 2005

These are the seed capsules of bladder senna, in which the caterpillars grow.

This is a bladder senna bush with almost all the flowers developed into seed pods...

... while this is another, in the same site, on the same day, with mostly flowers. The male blues show much more interest in these yellow bushes.

Iolana iolas distribution

Distribution

This is one of my all-time favourite butterflies. It is a magnificent insect - the largest European blue - and generally rare, giving it extra cachet. In Europe, it is restricted to the south, where it flies in hot places where its foodplant, bladder senna, grows. Because this plant often grows in isolated patches within a larger area, the butterfly is very mobile, males frequently covering many kilometres a day as they check all the bushes for females.

Once you have seen an iolas blue there is no possibility of confusing it with anything else. It is not only larger than other blues but much more athletic, effortlessly bounding from one bladder senna bush to the next, and then on again. Males in search of females are best watched from a distance rather than pursued. Fortunately, they do quite frequently stop to sun or nectar, especially in the morning, and then good views are possible. Mostly they stop on bladder senna but they will occasionally use other nectar sources. Males will also take minerals on the ground. Points to look out for if you have not seen one before and want to be sure include the expansive, sky-blue uppersides of the males, with narrow dark borders gently tapering to the forewing apex, the extensive dark suffusion of the females, with blue bases to the wings, and in both sexes the pale undersides with white lunules where other blues have orange. Green-underside blues often fly in the same places and may be superficially similar but even the biggest are smaller than the smallest iolas blues and they are far less impressive on the wing.

There is a single brood, lasting from May (or occasionally the end of April) until June. The books say there may be a partial second brood later in the year but I have never witnessed this, nor seen bladder senna in flower then. Caterpillars feed up in the bladders of the foodplant and then pupate on the ground, under stones, nearby. They spend the winter as pupae.

An interesting piece of trivia: the last person officially to record an iolas blue at Bex (actually, near Bex), my first point of call when I visit the Valley, was Vladimir Nabokov, of Lolita fame - a noted lepidoperist who lived in Switzerland towards the end of his life.