The silver-studded blue (Plebejus argus) is a butterfly in the family Lycaenidae. It has bright blue wings rimmed in black with white edges and silver spots on its hindwings, lending it the name of the silver-studded blue. P. argus can be found across Europe and east across the Palearctic, but it is most often studied in the United Kingdom where the species has experienced a severe decline in population due to habitat loss and fragmentation.
P. argus engages in mutualism with ants that contribute to the butterflies' reproductive fitness by providing protection from predation and parasitism from the point of egg laying to their emergence as adults. P. argus adults emerge at the end of June and beginning of July and engage in flight until the beginning of August.
The butterfly is adaptable to different habitats and is found in heathland, mossland, and limestone grassland. Tending towards a sedentary lifestyle and typically flying less than 20 metres (66 ft) a day, P. argus maintains a small radius home range. Their habitats lend themselves well to both foraging and egg laying as the host plants are ubiquitous in all three environments they occupy.
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P. argus is found across the Palearctic. In the United Kingdom, the butterfly experienced a severe decline in population during the nineteenth and twentieth centuries. P. argus is generally considered to be endangered and extinct in the Northern United Kingdom and are primarily found in the Southern and Western portions of the United Kingdom.
P. argus resides in heathland, mossland, and limestone grassland.
Heathlands are able to meet the needs of P. argus due to burning, cutting, and other disruptions of mature heaths. With these disruptions, the habitat becomes conducive to habitation by P. argus because of the high cover of E. cinerea and short C. vulgaris that is able to form a landscape with the patches of bare ground. This is characteristic of heathland at an early stage of development. This environment is suitable until the point at which the shrubs native to the environment mature and obscure the bare ground and vegetation margins that the butterflies use for oviposition.
Mossland, similar in nature to wet heathland, has soil primarily composed of peat which supports one of the families of host plants of P. argus, Ericaceae. This host plant grows alongside other grasses, sedges, and rushes. While the main disturbance to heathland is quarrying, mossland faces peat digging which contributes to the transient and shifting nature of this particular habitat.
The hostplants of the first two environments, Ericaceae and Leguminosae, are less present in the third environment, limestone grassland. In this environment, the host plants of P. argus are primarily herbaceous Cistaceae as well as Leguminosae. In limestone grassland, the bare ground and vegetation margins instrumental to the life cycle of P. argus are created through grazing by other animals as well as by disruption of the habitat by natural disturbance of the stoney topography of this environment.
P. argus use shrubs for roosting, resting, basking, mate location, and shelter and for this reason, they tend to be found in higher numbers close to locations that are dense in shrubs. Most of the population gathers around these shrubs during weather that is colder, cloudy, and windier. When the weather is warm, sunny, and the breeze is still, P. argus spends less time in shrub dense habitats and more time in flight and finding host plants in areas rich in calcareous heath. These areas tend to be on exposed hillsides. For this reason, it often appears that the habitat of P. argus shifts with weather conditions.
In addition to choice of habitat due to host plants and topography, P. argus density correlates with the densities of nest of the butterflies' mutualist ants, Lasius niger and Lasius alienus.
Adult P. argus tend to be very sedentary, only moving around 20 metres (66 ft) every day. For this reason, the butterflies colonize on discrete territory and patches of land. Some butterflies, though, disperse and move over a kilometer between colonies. This is rare, however, as these butterflies tend to form metapopulations.
Adults feed on nectar.
The life cycles of Plebejus argus are divided into four main stages: eggs, larvae, pupa, and adults.
When a male detects a female sitting quiescently, he flies towards the female. As he approaches the female, he flutters his wings in broad sweeping movements and she raises her abdomen while vibrating her half-open wings in a mate refusal posture. The female then flies away and is followed by the male. Once she lands, the male flutters around, either in the air before descending or after landing. The female displays a receptive posture by folding her wings after which the male positions himself parallel to the female before bending his abdomen, spreading the valves, and exposing the copulatory apparatus. He proceeds to attach to the copulatory apparatus and the butterflies reorient themselves into the copulatory position. The intermediate aspects of sexual chase depend on the sexual receptiveness of the female to the advances of the male.
P. argus has undergone habitat loss and fragmentation in the United Kingdom due to the development of industrial agriculture, new forestry practices, and landscape development. Additionally, the percentage of heathland has decreased by over fifty percent in the United Kingdom, greatly affecting the butterflies for which this was a primary habitat. The heathland that remained was reduced in quality due to shifting environmental influences. Rabbits helped keep vegetation short through grazing which was conducive to habitation by P. argus, but in the middle of the twentieth century, a virus, Myxomatosis, caused a significant decline in the population of rabbits and therefore the grass length grew to a point that was no longer conducive to the butterflies.
