The dark anteater (Phengaris nausithous) is not one of the most spectacular butterflies in Europe, but it is one of the most endangered. This species is called an anthill because of its peculiar reproduction cycle. It lives in very humid meadows, where the greater sanguisorba is found, its only nutritious plant. The eggs are laid on the flowers of the sanguisorba in the months of July and August. After 3-5 days, the small caterpillars are born, which two weeks later are dropped from the plant and are picked up by ants of the genus Myrmica. This situation occurs at dusk, when the activity of ants of this genus is at its maximum, so the caterpillar ensures that it is picked up by this type of ants and not by others that would prey on them. Once inside the anthill, the caterpillars feed on the larvae of the ants for more than ten months, also chrysaling in the subsoil from June. This curious behavior that ensures that the caterpillars are not attacked by ants and are cared for and fed by them, is due to the secretion of pheromones emitted by the caterpillars of the butterfly and that imitate the smell of ant larvae.

A project of the Association of Palencia Naturalists has made it possible to discover an important population of this insect in the Palencia Mountain, where several initiatives have been carried out to conserve it, especially through the signing of very long-term land stewardship agreements with the farmers of the area to guarantee the maintenance of the humid meadows where this species lives. in addition to carrying out an environmental education campaign in five educational centers in the area. Thanks to this project, almost 600 specimens of dark anteater were counted in 34 previously unknown colonies . This means that approximately half of the known Spanish population is located in Palencia, in the Natural Park of Fuentes Carrionas and Fuente Cobre-Montaña Palentina.

Despite these encouraging data, this butterfly has a very small population in Spain and is possibly suffering a sharp decline, similar to that of European populations. For these reasons, the dark anteater is listed as vulnerable in the National Catalogue of Endangered Species and its populations require “strict protection” according to the European Habitat Directive.

This small lepidoptera is a species linked to the livestock landscape, and changes in the uses of pastures, such as excessive livestock pressure, abandonment of it, with the consequent occupation by weeds, or too intense mowing without leaving edges, can cause the disappearance of the nutritive plant and therefore that of the butterfly.

This work is now being complemented by the implementation of the “Technical bases for the conservation of threatened lepidoptera species”, whose objective is to make an inventory of all the colonies of the dark anteater and that will allow the drafting of technical bases that allow the subsequent drafting and approval of a Conservation Plan for the dark anteater, as required by Law 42/2007. Both projects are supported by the Biodiversity Foundation of the Ministry of Agriculture, Food and the Environment.