Like some other species of Lycaenidae, the larval (caterpillar) stage of P. alcon depends on support by certain ants; it is therefore known as a myrmecophile.

Alcon larvae leave the food plant when they have grown sufficiently (4th instar) and wait on the ground below to be discovered by ants.
The larvae emit surface chemicals (allomones) that closely match those of ant larvae, causing the ants to carry the Alcon larvae into their nests and place them in their brood chambers.
Once adopted into a nest, Alcon larvae are fed the regurgitations of nurse ants (just as other ant brood), a process called trophallaxis.
This parasitic method is known as the "cuckoo" strategy and is an alternative to the predatory strategy employed by most other members of the genus such as Phengaris arion.
Though less common, the cuckoo strategy has been found to have several advantages over the predatory strategy.
For one, it is more trophically efficient than preying directly on other ant grubs, and as a result, significantly more cuckoo-type larvae can be supported per nest than predatory larvae.
Another advantage of cuckoo feeding is that individuals, having pursued a higher degree of social integration, have a higher chance of surviving when a nest is overcrowded or facing food shortage because ants preferentially feed the larvae; compared to the type of scramble competition that can devastate predatory larvae, this contest competition results in much lower mortality.
Though the cuckoo strategy has its advantages, it also comes with important costs; with greater host ant specialization comes much more limited ecological niches.

When the Alcon larva is fully developed it pupates.
Once the adult hatches it will leave the ant nest.

Over time, some ant colonies that are parasitized in this manner will slightly change their larva chemicals as a defence, leading to an evolutionary "arms race" between the two species.

Generally, Lycaenidae species which have a myrmecophilous relationship with the ant genus Myrmica are locked to primary host specificity.
The Alcon blue is unusual in this regard in that it uses different host species in different locations throughout Europe, and often uses multiple host species even within the same location and population.
Though it may be adopted into the nests of multiple Myrmica species within a given site, there is typically one "primary" species with which the locally adapted larvae can best socially integrate, leading to drastically higher survival rates.
Across Europe, Alcons are known to use Myrmica scabrinodis, Myrmica ruginodis, Myrmica rubra, Myrmica sabuleti, Myrmica scabrinodis, Myrmica schencki, and rarely Myrmica lonae, and Myrmica specioides.
Like some other species of Lycaenidae, the larval (caterpillar) stage of P. alcon depends on support by certain ants; it is therefore known as a myrmecophile.
Alcon larvae leave the food plant when they have grown sufficiently (4th instar) and wait on the ground below to be discovered by ants. The larvae emit surface chemicals (allomones) that closely match those of ant larvae, causing the ants to carry the Alcon larvae into their nests and place them in their brood chambers. Once adopted into a nest, Alcon larvae are fed the regurgitations of nurse ants (just as other ant brood), a process called trophallaxis. This parasitic method is known as the "cuckoo" strategy and is an alternative to the predatory strategy employed by most other members of the genus such as Phengaris arion. Though less common, the cuckoo strategy has been found to have several advantages over the predatory strategy. For one, it is more trophically efficient than preying directly on other ant grubs, and as a result, significantly more cuckoo-type larvae can be supported per nest than predatory larvae. Another advantage of cuckoo feeding is that individuals, having pursued a higher degree of social integration, have a higher chance of surviving when a nest is overcrowded or facing food shortage because ants preferentially feed the larvae; compared to the type of scramble competition that can devastate predatory larvae, this contest competition results in much lower mortality. Though the cuckoo strategy has its advantages, it also comes with important costs; with greater host ant specialization comes much more limited ecological niches.
When the Alcon larva is fully developed it pupates. Once the adult hatches it will leave the ant nest.
Over time, some ant colonies that are parasitized in this manner will slightly change their larva chemicals as a defence, leading to an evolutionary "arms race" between the two species.
Generally, Lycaenidae species which have a myrmecophilous relationship with the ant genus Myrmica are locked to primary host specificity. The Alcon blue is unusual in this regard in that it uses different host species in different locations throughout Europe, and often uses multiple host species even within the same location and population. Though it may be adopted into the nests of multiple Myrmica species within a given site, there is typically one "primary" species with which the locally adapted larvae can best socially integrate, leading to drastically higher survival rates. Across Europe, Alcons are known to use Myrmica scabrinodis, Myrmica ruginodis, Myrmica rubra, Myrmica sabuleti, Myrmica scabrinodis, Myrmica schencki, and rarely Myrmica lonae, and Myrmica specioides.
Phengaris alcon