Our canton is home to 80% of the approximately 196 species of diurnal butterflies listed in Switzerland, half of which are on the Red List. This shows the responsibility of the Valais for the preservation of these graceful pollinators, of which our territory is perhaps the last or only bastion.
In vain sometimes! The very rare hermit has definitely disappeared from its last place of observation, the steppe lawns around the Bâtiaz tower.
If butterflies always amaze the general public, caterpillars – which are an integral part of their cycle – also deserve our attention.
The azure sylvain, an elegant and uncommon forest species. ©Jérôme Fournier
These “ladies”, of great beauty depending on the species (see the swallowtail caterpillar!), are remarkable in more ways than one. The caterpillars of the azures of the croisette and the serpolet have a sacred tactic to finish their development passively, fed, housed and protected in an anthill.
They emit irresistible pheromones from their host plant to get adopted by a specific species of ants!
Now rarer: the pretty caterpillar of the flambé, a butterfly linked to dry and open environments, grows on rustic and thorny shrubs, blackthorn trees called blackthorn or Saint Lucia wood. ©Jérôme Fournier
Let’s once again lift the veil on another extraordinary phenomenon: how do individuals of the many species of the same family manage to mate with the right partner? “Each species has its own genitalia,” reveals biologist and entomologist Jérôme Fournier.
“Their shapes are highly variable and only fit together when there is a species match.” The scientist also resorts to the examination of these genitalia. An infallible identification criterion! The world of butterflies has not finished surprising us…
United for the worst and the best
Sometimes there is a very specific relationship between a butterfly and its host plant. The decline of the plant will lead to that of the pollinator. The survival of some butterflies is intimately linked to a single plant species.
This is the case for the azure of the baguette tree. This pretty blue butterfly colonizes the driest and sunniest hillsides, where its only host shrub, the baguette tree, grows.
Jérôme Fournier, biologist, entomologist-ornithologist at Drosera applied ecology SA and biology teacher at the Collège de St-Maurice. ©DR
The female lays her eggs in flowers or fruit. The caterpillar feeds on seeds before pupating under a pebble at the foot of the bush. “The azure of the baguette tree is classified as a high priority in terms of conservation” specifies the biologist Jérôme Fournier.
“It is maintained on the south side of central Valais, thanks in particular to a program of planting many baguette trees!”
Other butterflies are less demanding. “The magnificently colored swallowtail lays eggs indifferently on the umbelliferae. It therefore also breeds in vegetable gardens, on carrots and fennel.”
Everyone has their own way of working: the Apollo, a large sailboat with diaphanous wings, lives in dry meadows and rocky environments in the middle mountains, generally below the upper limit of the forest. So many areas covered with stonecrops which feed its caterpillar.
The little apollon is a mountain dweller, only visible along torrents, runoff, marshy or fontinal environments, where the host plant of its caterpillar, the stream saxifrage, grows. ©Jérôme Fournier
The large Apollo, excessively collected by collectors because of the variability of its ornamentation, is now protected.© Jérôme Fournier
Species of butterflies associated with peat bogs and wet meadows are much rarer in Valais and highly threatened. “The bistort copper, whose host plant is none other than the bistort knotweed, is however visible locally in the Illiez valley. The male has beautiful purple reflections and the female, small purple spots.
Natural habitats under high tension
The life expectancy of adult butterflies is highly variable but rather short: from a few days to several months (even up to 9-10 months for the lemon), depending on the species, if they manage to escape their predators (birds, batrachians, reptiles, etc.).
The intensification of agricultural practices and the destruction of natural habitats have a heavy impact on the mortality and disappearance of species. “The plain has become a desert for the butterflies and the more recent decline of their populations can now be seen in the mountains,” explains the biologist.
The flamboyant copper lays on the sorrel and follows its plant to the mountains at 2000 meters. ©Jérôme Fournier
“The bushiness of grasslands sounds the death knell for butterfly species in open environments. Sprinkler irrigation is dramatic for the development of the caterpillars as well as for the flora, the sources of nectar dry up.”
“Intensive purination increases plant biomass, but to the detriment of floristic composition and diversity, including host plants for butterflies.”
So what to do to reverse the trend? “Favor flowery meadows, lean meadows, whether dry or wet, with a maximum of plant species. Plant native bushes, mow late when the seed cycle is complete and implement conservation measures.”
Threatened at the Swiss level, the bacchante, linked to the open forests and semi-shaded grassy edges of low altitude, has suffered from changes in the traditional exploitation of forests, the tarring of forest roads or on the edge.
The bacchante, considered very threatened at the Swiss level, is observed in the Valais Chablais and very locally in the central Valais, at the beginning of June. ©Jérôme Fournier
The application of forest management measures in favor of this butterfly, present in Bois-Noir in Saint-Maurice and to a lesser extent in the Chablais region of Valais, is of particular importance for this species and can also be beneficial to d other forest butterflies.
Same fight for the toadflax melite, an endemic subspecies of Valais, whose distribution is now limited to two population centers, located in the regions of Martigny (Fully-Saillon) and Viège (Saastal).
Endangered: the berisalii subspecies of the toadflax moth in Valais does not occur anywhere else in the world. ©Jérôme Fournier
“This butterfly is dependent on Narrow-leaved Toadflax, growing in steppe grasslands. The regression of the plant is mainly explained by the disappearance of its habitat on the edge of disturbed land and traditional vines. continues the biologist.
“Two successive projects aimed at favoring the host plant and therefore its butterfly have been set up in the two regions. They consist of sowing and planting young shoots of this host plant. The final objective being the genetic exchange between populations of toadflax moths.”
This article can be read for free from May 23 in our magazine “Terroirs” here