The invertebrates are the group having a species highest number in the Sierra de Guadarrama National Park. Its high diversity and adaptability to the environment climatic conditions -low temperatures, high snowfall and rainfall, strong winds and high solar radiation - shorten its biological cycle. These extreme variables have led to fundamentally different adaptive strategies in insects, from singular shapes and reduced sizes to the most diverse range of colors, such as the ornamentation of coleopteran elytra or the striking chromatism of butterflies.
In the National Park, spring and summer are time par excellence for a show: a period when insect larvae, after spending winter under the ground, snow and ice, emerge in their adult stages. This metamorphosis process all insects share, causes an explosion of life and triggers a race against time to ensure descent in years to come.
Within this invertebrate fauna, the group having a greatest biodiversity is the one of arthropods, headed by the insect class. However, there are other less abundant but very interesting groups, such as molluscs and crustaceans, mainly ln the National Park wetlands.
Among the molluscs are Pisidium casertanum, characteristic in Peñalara Massif wetlands and National Park water streams. It is a bivalve about 4-5 mm long and under 4 mm width. It proliferates in lentic habitats loamy areas, and it has a cosmopolitan distribution throughout Europe.
Crustaceans, a class of arthropods, are typical of the National Park quiet waters ecosystems. They are usually small invertebrates including, among others, species from Daphnia, Ceriodaphnia, Alona, and Chidorus genera. Perhaps one of the most striking crustaceans is Chirocephalus diaphanus, an anostracean about 37 mm long with a Palearctic distribution. In the National Park, it is distributed in temporary lake systems having oligotrophic waters, and it comes to survive to over 2,100 m heights. Their populations appear in summer, when the snowpack is removed from the mountain wetlands. It is monocyclic, so its eggs need a period of drying prior to hatching.
As mentioned, the largest and most representative group the one from the insects. It is globally estimated that 70% to 80% of living beings are insects. Currently 900,000 insects species are known worldwide. For the Sierra de Guadarrama, the species range estimated number is 15,000 to 20,000 insects, ie, 1.65% of the world total and 35.5% of the insects in the Iberian Peninsula.
Lepidoptera belong to the most striking, showy, and best studied order in the Sierra de Guadarrama. There are 124 rhopalocerae (day butterflies) species of, from 224 classified in the Iberian Peninsula, that is to say, 55% of the Iberian species are distributed in the Sierra de Guadarrama.
EThe presence of the Apollo butterfly, Parnassius Apollo, is noticeable. It belongs to the Papilionidae family; its size is variable: 60 to 75 mm, and the colorful stands out in his white wings of 4 red ocelli, surounded in black. Its distribution in the National Park of the Sierra de Guadarrama is limited to mountainous areas, on alpine slope meadows, and bogs and sunny humid zones. There exist several isolated populations in the Iberian peninsula mountainous zones, being known more than 20 subspecies. In the Sierra de Guadarrama, the escalerai and wyatti subspecies have been mentioned. Its main nutritious plant is Sedum. With regard to its protection level, it is classified as extinction risk status at the Community of Madrid level, and it is mentioned in the Habitats Directive Annex IV, in Berne Convention Annex II, and the List of Wild Species under Special Protection Regime.
The harlequin butterfly, Zerinthya ruminina, is a papilonidous, living in the National Park boundaries areas under 1,500 m height. It is a medium size (50 mm) butterfly, very characteristic for its multicolored winged (yellow, black and red); it is little demanding in terms of habitat, although it is limited to oak trees area, where it is nutritious plant, Aristolochia, is available. It is classified as special interest status at the community of Madrid level.
Another very particular butterfly is the dusky large blue, Phengaris nausithous, living in the Sierra de Guadarrama Valley of El Paula area. It is a small size species from Lycaenida family, being limited to 4 localities in the Iberian Peninsula. It is classified as vulnerable status in the National Catalog, as well as the Habitats Directive Annexes II and IV, and the Berne Convention Annex II.
Other butterflies very significant in the Sierra de Guadarrama, both for their history as for their singularity and fragility are the heterocerae -or night butterflies-. Specially, the Spanish moon moth (Graellsia isabelae), a large size saturnid, which reaches 10 cm in wingspan. It was described and discovered in the Sierra de Guadarrama by Mariano de la Paz Graells, in year 1848. Although initially named Saturnia isabelae in honor to Queen Isabel II, it was later discovered that it belonged to another different genus, denominating Graellsia, in honor to Dr. Graells. He discovered not only this lepidopteran, but he also described several species of coleopterans. The so called "Graellsia” in the mountains environments, has wings with a semi-transparent clear greenish coloration, with chestnut stripes that mark its veins, very practical when concealing in Pinus sylvestris forests. It is classified as special interest at the Community of Madrid level, and it is included in the Wild Species List under Special Protection Regime, the Habitats Directive Annexes II and IV, and Berne Convention Annex II. Although a small population exists in the Alps, it is thought that it was introduced, reason why it is considered an Iberian Peninsula endemism.
By size, the great peacock moth (Saturnia pyri) is another great heterocean. It reaches 130 mm and is considered the largest lepidopteran in Europe. Its forewings and hind wings are ocher to grayish, with reddish tones zigzagging lines, and they have four very marked ocher, brown, ocher and black ocelli. Its larva is of great size reaching until 10 cm length. It is distributed throughout Europe. In the Sierra de Guadarrama has been located in Miraflores, Rascafría and Cercedilla areas. Its regression in the community of Madrid zone has led to the classification as special interest status.
Other butterflies classified as vulnerable status at the Community of Madrid level are Nymphalis antiopa, Ocnogyna latreillei and Euphydryas aurinia. The latter is even included in the List of Wild Species in Protection Regime and both the Habitats Directive and Berne Convention Annex II. Plebicula nivescens is another rhopaloceran classified as sensitive to habitat alteration status at the Community of Madrid level. It is a Spanish mountain endemism. The subspecies estevita is the one that inhabits in the Guadarrama Mountain range of and is a local endemism.