Thursday, 9 February 2017

Conserving the Large Blue Butterfly in the Touraine

The Large Blue butterfly Maculinea arion (Fr. l'Azure du serpolet) is classified as vulnerable in Indre et Loire and endangered in Europe. In the Touraine the adults can be on the wing from the beginning of June to mid-September, varying a bit depending on the flowering of its caterpillar host plant, Wild Oregano Origanum vulgare (Fr. Origan). They tend to fly later rather than earlier in the season, peaking in July-August. The average life span of the adult butterflies is 3 days although they can live up to 17 days. The species as a whole might be on the wing for as little as 15 days in one year, and up to 36 days in another. In that period, each female will lay about 60 eggs. The first three stages of the caterpillars live in the oregano flowers. For the last stage, at the end of the summer, the caterpillars move into an ants' nest. These caterpillars may pupate and emerge as an adult butterfly at the end of the following spring, or remain in the ants nest for another year, emerging slightly earlier than the ones which just overwinter once in the ants nest.

Large Blue female on Wild Oregano flowers.

Unlike the Large Blues in the north and in the mountains, our central lowland French Large Blues don't use thyme rich grasslands. Instead they occupy rough calcareous grasslands that are scrubbing over or are on the edge of woodland and rich in Wild Oregano. They need an area of several square metres with oregano flowers poking up above the vegetation, and with the presence of the ant Myrmica sabuleti nests near the base of the oregano plants (within a metre or two). Each patch of oregano may host a small colony of Large Blues and to maintain the meta-population each patch needs to be no more than 200-400 metres apart. The butterflies don't move very far. The grassland needs to be pasture or haymeadow which is grazed or mowed late in the season so as not to disrupt the butterfly's lifecycle.

Ovipositing (egg laying) on oregano flowers.

The Large Blue is regularly recorded in the Brenne (in Indre 36) and the Touraine (Indre et Loire 37), rarely in Loir et Cher. The Brenne/Touraine population is considered reliably abundant and more or less continuous. It is not considered threatened in the short term, but there are fears for the medium term because of agricultural practices and the fragmentation of habitat. In Berry and Loir et Cher the few records are considered to be a relict population, scattered and isolated.

Checking over the oregano flowers prior to ovipositing.

If you want to see this lovely butterfly, the best places are the valleys of the Claise and its tributaries, the valley of the Changeon, the Puys du Chinonais, the Eperon du Murat (near Ferrière Larçon) in the Touraine and the valleys of the Creuse and its tributaries in the Brenne. At least, this is where the most records come from -- it might just reflect the distribution of butterfly observers who send their records to the National Natural History Museum in Paris...

Showing the dove grey underside of the wings.

There are three priorities to focus on in the regional protection plan for this species and the other two Maculinea species that occur in the region:
  1. Learn more about the ant hosts.
  2. Protect, manage and improve the habitat to combat fragmentation and allow meta-populations to move between micro-habitats.
  3. Diffuse and co-ordinate new research and existing knowledge about the species effectively throughout the network of conservation organisations who work to protect and monitor the species.
The plan is to achieve the above by surveying to establish the current distribution of the three species; establish exactly which species of Myrmica host ants are in the region; repeated surveying to establish the population numbers of the three species in the region; map the sites on which Maculinea spp occur in the region; ensure the sites are adequately protected; ensure the protection of corridors between habitats; conduct experiments to establish best habitat management practice; train professionals in the field and establish a network of professionals for information exchange. The budget for achieving all of this was €88 800 last year.


Ken Broadhurst said...

Nice photos, especially the third one. I see these butterflies often every summer. Maybe that's because we live on the extreme southern edge of the Loir-et-Cher.

chm said...

It seems to me that serpolet and origan, whether wild or otherwise, are two different plants of the same family, Lamiac eae.

Serpolet is Thymus serpyllum and Origan, as you said, is Origanum vulgare. Are they both host plants, or only serpolet as the French name implies? If it is the latter, is serpolet more abundant than origan?

Sheila said...

Calling E.O. Wilson. As you've pointed out in the past, the symbiotic relationship between these two is the basis for the butterfly's survival. Come to think about it, though, what do the
ants gain? As Ken says, wonderful photos.

chm said...

I just checked the Wikipedia entries for Large blue and Azuré du serpolet and I found complementing information. The French entry says there are several thyme and origan host plants in addition to serpolet: Thymus praecox, Thymus marschalliana, and Origanum vulgare. So that answers my question.

Now, the choice of the host plant by the female Azuré depends on the nearby presence of nests of a specific ant so the caterpillar that lets itself drop to the ground when ready can be picked up by the ants and carried inside the nest. It doesn't say if the caterpillar looks like and is the same color as the seeds that ants gather normally.

Inside the nest the Azuré caterpillar will feed on ants larvae.

chm said...

Sheila, in this "game" the ant seems to be the loser!

Susan said...

I think it is unlikely you are seeing this species where you are. There are only a couple of records of them in Loir et Cher, and they are in the Sologne. If you've got photos though that can be used to ID Large Blue in Loir et Cher I'm sure the museum would be interested to know. Most probably what you see is the Common Blue Polyommatus icarus, which are smaller, bluer and do not have the big black spots on the upper side (and a more complicated arrangement of spots on the underside).

Susan said...

The caterpillar looks like the ant larvae, and more importantly, smells like the ant larvae.

Susan said...

That's right. This is an endoparasitic relationship, where the parasite kills the host. One of the reasons these butterflies are rare is because the species cannot afford to overload the hosts.

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