Common blue

The common blue butterfly or European common blue (Polyommatus icarus) is a butterfly in the family Lycaenidae and subfamily Polyommatinae. The butterfly is found throughout the Palearctic and has been introduced to North America. Butterflies in the Polyommatinae are collectively called blues, from the coloring of the wings. Common blue males usually have wings that are blue above with a black-brown border and a white fringe. The females are usually brown above with a blue dusting and orange spots.

Taxonomy and phylogeny

This species was first described by Siegmund Adrian von Rottemburg in 1775. Vernacular names that have been given to P. icarus include little blew argus, blew argus, mixed argus, selvedg'd argus, ultramarine blue, caerulean butterfly, and alexis.

Subspecies

Subspecies include:

P. i. icarus (Europe, Caucasus, Transcaucasia)
P. i. mariscolore (Kane, 1893) (Ireland)
P. i. fuchsi (Sheljuzhko, 1928) (South Siberia, Transbaikalia)
P. i. omelkoi Dubatolov & Korshunov, 1995 (Amur, Ussuri)
P. i. ammosovi (Kurenzov, 1970) (Central Yakutia, Far East, Kamchatka)
P. i. fugitiva (Butler, 1881) (Pakistan)
P. i. napaea (Grum-Grshimailo, 1891) (Tian-Shan)
P. i. zelleri Verity, 1919

Common blue (Polyommatus icarus mariscolore) female Burren.jpg|female P. i. mariscolore, County Clare, Ireland

Common blues (Polyommatus icarus mariscolore) mating Burren.jpg|mating P. i. mariscolore, County Clare, Ireland

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Description

Polyommatus icarus has a wingspan of . The dorsal side of the wings is an iridescent lilac blue, bright violet-blue, or almost hyacinth-blue with a thin black border. Females' wings are brown or black-brown with a row of red reddish yellow spots along the edges of the wings (marginal spots) and usually some blue at the base. The extent of blue and brown is extremely variable depending on location. The top of the wings in the female may be mostly blue, especially in Ireland and Scotland, but it always has red spots.

The ventral side has a greyish or dust-grey base colour in the males and a more brownish hue in the females.

Geographic range

thumb|Underside

The common blue butterfly is found in Europe, North Africa, the Canary Islands, and east across the Palearctic to Northern China. Recently it was discovered in Quebec, Canada. It is widespread in the British Isles. Its distribution trend shows a 15% decline since the 1970s. It was discovered in Mirabel, Quebec, Canada, by Ara Sarafian, an amateur entomologist who observed the butterfly from 2005 to 2008. He contacted the Canadian National Collection of Insects in Ottawa where the butterfly was identified as Polyommatus icarus, a newly introduced butterfly to Canada and to North America. The butterfly seems to be well established and is extending its range from year to year. A study from Montreal, Quebec, Canada showed that the common blue is most abundant in areas with greater urban land cover and where their preferred larval host plant, bird's foot trefoil (Lotus corniculatus), can be found. This host plant is a favored plant for two reasons: it provides adult nutrition, as well as food for the larva after it hatches.

Food resources

Larval food plants

The larvae feed on plants from the bean family, Leguminosae. Recorded food plants are Lathyrus species, Vicia species, Vicia cracca, Oxytropis campestris, bird's foot trefoil (Lotus corniculatus), Oxytropis pyrenaica, Astragalus aristatus, Astragalus onobrychis, Astragalus pinetorum, black medick (Medicago lupulina), Medicago romanica, Medicago falcata, common restharrow (Ononis repens), wild thyme Thymus serpyllum, lesser trefoil (Trifolium dubium), Trifolium pratense and white clover (Trifolium repens). There are also some other advantages of sequestering flavonoids, including the protection of eggs from adverse UV chemical reactions, as the butterflies will absorb the UV rays, and the flavonoids can offer a chemical defense against predators or pathogens.

Flavonoid sequestration is much more effective when coming from natural host plants than from experimentally offered diets. Females sequester about 60% more flavonoids than do males. This richness in females may increase visibility, but could also confer information about feeding history, and consequentially the quality of potential mate. Flavonoid sequestration is an important component of intraspecific visual communication and sexual signaling in Polyommatus butterflies.

Parental care

Oviposition

During oviposition, females must locate a potential host plant and evaluate its suitability as the host plant for oviposition. P. icarus uses visual cues to conduct this task. Females use several plants in the family Fabaceae as larval host plants, many which could also potentially function as nectar sources. P. icarus prefers plants with flowers over plants without, and prefers to oviposit near the flowers. The ground color of the egg sac is pale-greenish grey, with the actual arrangement being white. Eggs are laid singly on young shoots of the food plant.

Larvae

The larvae emerge around a week or two after eggs are laid. The larvae of P. icarus feed on the underside of leaves, causing blotching. Hibernation occurs as a half-grown larvae. They are attractive to ants of genera Myrmica, Lasius, Formica, Plagiolepis which will often take it into their nests. The larva creates a substance called honeydew, which the ants eat while the butterfly lives in the ant hill. The relationship between these ants and blue common larvae is described to be facultatively mutualistic.

Etymology

Named in the Classical tradition. In Greek mythology, Icarus was the son of the master craftsman Daedalus, the architect of the labyrinth of Crete.