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Common Blue

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description Common Blue Overview

The Common Blue (Polyommatus icarus) is a small butterfly belonging to the Lycaenidae family, predominantly found across Europe and temperate Asia. It exhibits significant sexual dimorphism; males possess vivid violet-blue upper wings, whereas females are primarily brown with a variable amount of blue scaling. This species thrives in grassy habitats, including meadows, heaths, and roadside verges, where its primary larval food plants, such as bird's-foot trefoil, grow abundantly. It is recognized as one of the most widespread and frequently encountered blue butterflies in the United Kingdom.

help Common Blue FAQ

What species is the Common Blue butterfly?

In Europe, the Common Blue is Polyommatus icarus, a small lycaenid butterfly found across much of Europe and temperate Asia. It is a different species from the similarly named Adonis Blue, Lysandra bellargus. [UK Butterfly Monitoring Scheme](https://ukbms.org/species/common-blue)

How can you tell a male Common Blue from a female?

Males usually have bright violet-blue upper wings, while females are more brown or brown-violet and may show orange markings. The underside of the wings is gray-brown with dark spots, which helps identify Polyommatus icarus in the field. [Butterfly Conservation atlas](https://butterfly-conservation.org/sites/default/files/2024-04/Highland%20Butterfly%20Atlas%202022%20Online.pdf)

What plants do Common Blue caterpillars eat?

The main larval food plant is Bird's-foot Trefoil, Lotus corniculatus, while Black Medick, Medicago lupulina, is another important food plant. These legumes explain why the butterfly is closely associated with herb-rich grassland. [UK Butterfly Monitoring Scheme](https://ukbms.org/species/common-blue)

Where do Common Blue butterflies live?

Polyommatus icarus lives in herb-rich grassland, verges, and other disturbed sites where its legume food plants grow. In Britain it is widespread, but the UK monitoring record links its long-term decline to the loss of semi-natural grassland. [UK Butterfly Monitoring Scheme](https://ukbms.org/species/common-blue)

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