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Iolas Blue Iolana iolas in the Province of Segovia : June 2014

John Muddeman
06/07/2014 22:22:44

A short walk at a new spot in a favourite area of mine, three years after finding Bladder Senna, the larval food plant, paid off with the discovery of a small colony of this very scarce and rather enigmatic species.

Posted in: Flora, Butterflies and Moths, Endangered Wildlife and Habitats | Castile-Leon | Mainland Spain, Central Spain

The Hoces del Río Duratón park in the A male Iolas Blue - Iolana iolas © John MuddemanA stunning male Iolas Blue
Iolana iolas
© John Muddeman
Province of Segovia is well known amongst birdwatchers as one of the THE sites in Spain to look for the scarce, declining and often difficult-to-see Dupont's Lark Chersophilus duponti. While the limestone plateau is famous for this and other interesting bird species, such as seven other lark species, Western Black-eared Wheatear Oenanthe hispanica, Spectacled Warbler Sylvia conspicillata and Western Orphean Warbler Sylvia hortensis amongst others, the tremendous variations in the landscapes afforded by the deep gorges and the variety of habitats resulting from variations in humidity, aspect and soils mean that it is also very rich in other flora and fauna.

In late June 2011 I visited the general area while prospecting new routes, which including finding a mating pair of Yellow Clubtail Gomphus simillimus dragonflies. These flew twice while being watched, and on the second occasion landed in a fruiting Bladder Senna Colutea hispanica bush. Not only was I delighted to find the dragonfly, which has very few records in general in C Spain, but I was also pleasantly surprised to see the bush, which I hadn't noticed in the area before, and immediately wondered if there could be Iolas Blue Iolana iolas present in the area.

Yellow-Clubtails - Gomphus-si © John MuddemanMating Yellow Clubtails on Bladder Senna
Gomphus simillimus
© John Muddeman
Given that I had previously guided a large group attending a conference in Madrid to the reserve, and that during the visit the park's director had noted that an on-going study in the reserve had revealed that over half of Spain's butterfly species were present, it seemed more than likely. Unfortunately however, as is so common here, this information (even in the form of a simple list), has never been made public.

Iolas Blue is a rather scarce butterfly, even in good areas and it appears that very few individuals can survive in most populations where individual Bladder Senna bushes or small clumps can be widely spread across large areas, with the subsequent risk of extinctions. They also appear to be rather flighty, and collecting has been an issue in some areas. Indeed, the species has attracted considerable attention virtually everywhere it occurs, e.g. with the species verging on extinction in Switzerland, and has consequently been the object of a number of studies here in Spain (and elsewhere) in an attempt to understand the food plant-butterfly relationship in order to help conserve the populations.

Indeed Iolana_iolas_distribution_(Iberian_Peninsula) © John MuddemanIolas Blue approximate distribution (Iberian Peninsula)© Joan Carles Hinojosa / Wikimedia Commons the species requires sufficient patches of large, actively flowering bushes, in sunny locations where ants of the Myrmica genus occur, in order to survive. Interestingly an MSc study in Switzerland discovered that adults survive for an average of just 3.6 days, and while females disperse twice as often as males, and over greater distances, movements over 550m are rare, though have been recorded up to almost 1.5km. In this study adults were only detected at 50% of all the food plant patches present, while in Spain local colonisations and extinctions were noted over an area of patches relating to the ability of the plants to flower and fruit, so providing habitat for the eggs and larvae (which feed exclusively inside the pods on the seeds, where they are also tended by ants!)

All in all, Iolas Blue is a really rather special species, requiring very specific conditions for continued survival, and being one of the largest European blues, with a short flight period and low density at possibly a completely new site, makes it all the more interesting to find!

Iolas-Blue - Iolana-iolas-und © John MuddemanIolas Blue feeding on Colutea flowers
Iolana iolas
© John Muddeman
The species shows a mainly Mediterranean distribution, ranging from NW Africa, very locally across S & E Spain, through S France and more widely eastwards across from Hungary and the Ukraine in the N, the Balkan Peninsula and Greece down through Turkey and Transcaucasia as far as Iran and Iraq. In Spain it is repeatedly quoted as being very locally present in the S and E, including being very local in Madrid (it is only found in three areas of the region), though a more recent general map shows a few centres of distribution in Spain.

In the light of my sighting, a thorough search through the internet throws up some interesting records for the species in the Province of Segovia. Eggs were discovered on seed pods of Bladder Senna collected in 2006 near Arganda del Duero (for use in repopulating the Hoces del Río Riaza reserve) and sent to Madrid for analysis. In 2006/7 the species was detected in the Sierra de Ayllón (along with over half of Spain's butterfly fauna!), and in May 2011, a single male was noted in a garden in a completely different area in the S of the province. Being that the host plant is apparently widely spread on the limestone substrates throughout the S & E of the province, it would seem fair to assume that small colonies of the Iolas blue may occur throughout too.

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