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.

[1] 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.

[1][5] Tending towards a sedentary lifestyle and typically flying less than 20 metres (66 ft) a day, P. argus maintains a small radius home range.

[6][1] Male P. argus have royal blue wings with a black border, white, wispy fringe, and metallic silver spots on the hindwings as well as spurs on their front legs.

This and the following species [argyrognomon] have in the anal area of the hindwing beneath on the black submarginal dots situated between the median branches and the submedian vein some metallic glittering scales which are usually not represented in our figures.

The upperside is deep dark blue, with a broad black border, argus is very similar to argyrognomon, but differs in quite a number of details, of which in the various individuals sometimes one sometimes another is more conspicuously developed.

On the upperside the blue gloss is deeper, darker, duller, with a slight violet tint and not so far extended to the margin, the latter being broader and appearing blacker; the row of dark submarginal dots which occasionally appear on the hindwing above in both species, therefore stands always in the black border in argus.

On the underside both sexes of argus have nearly always a strongly glittering blue-green dusting at the base of the wings, which is usually absent from argyrognomon; but we must add that also the inverse occurs, the blue basal dusting being absent from argus in exceptional cases and strongly marked in argyrognomon.

valesiana M.-Durr is frequently found among specimens from the Valais (but not exclusively and not constantly); it is distinguished by a yellowish grey underside and very small ocelli.

— A very large form is insularis Leech (78 d), from the north-island of Japan; its underside resembles hypochiona in its light pure ground-colour, but bears abundant and prominent black spots.

(78 d, e) is placed by Staudinger and Rebel as a variety of argus; it is a small form, which resembles hypochiona beneath, but is very dark above, with very thin red-yellow submarginal spots on the upperside of the hindwing, which are unfortunately not visible in our figure 78 d, the hindwing beneath bearing paler marginal spots; from the shores of the Black Sea, Armenia and Persia.

[ now full species Plebejus iburiensis (Butler, [1882])]belongs here; it is unknown to me in nature and was described from one specimen from Hokkaido; it appears to be a kind of albino of insularis.

They are common everywhere, especially on sandy soil, which also its ant prefers, but is said to noticeably decrease recently in numbers in some districts (e. g. in England).

Experiments have shown that species that have overlapping habitat distribution and are of similar color (according to the human eye) have distinct absorbance values within the UV range.

[9][5] 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.

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.

While the main disturbance to heathland is quarrying, mossland faces peat digging which contributes to the transient and shifting nature of this particular habitat.

[9] 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.

In limestone grasslands, P. argus lays eggs at the stem of Lotus corniculatus and at the base of Helianthemum chamaecistus.

[2][3] The life cycles of Plebejus argus are divided into four main stages: eggs, larvae, pupa, and adults.

[1] The adult butterfly lives only for about 4-5 days, and just a few weeks of rain during the mating season could wipe out entire colonies.

Once the eggs hatch, the ants chaperone the larvae, averting the attacks of predatory organisms like wasps and spiders as well as parasites.

In return, the ants receive a saccharine secretion fortified with amino acids from an eversible gland on the larvae's back.

[1][16] 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.