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Common blue butterfly

Insect

Polyommatus icarus

Male common blues have pale violet-blue upper wings with grey-beige undersides. However, females vary from those with predominantly brown upper wings and orange crescents, usually more common in the south, to those with more blue, found farther north and west.

This butterfly is common throughout the UK. There are often two broods, with eggs laid in June, then August and September. Common blue caterpillars hibernate and pupate in April and May giving rise to adults in May and June.

The caterpillars are short, green and furry. They feed on the underside of young leaves, leaving the upper leaf epidermis intact. This creates silvery blotches on the leaves that are easy to spot.

The caterpillars secrete nutrient-containing substances that attract ants. In turn, the ants protect the caterpillar from predators. Ants probably tend the chrysalis too.

What does it eat?

Adults drink nectar from flat-headed flowers. Caterpillars eat wild, leguminous plants such as bird's-foot trefoil, rest harrow and white clover.

When will I see it?

Adults between May and September, sometimes October in warm years. Caterpillars are present throughout the year except May and late July-early August.

Where will I see it?

Feeding on a variety of flat-headed flowers, basking in the sunshine. Caterpillars on young, leguminous plants such as white clover. Also in grassland, grassy dunes, meadows, woodland clearings, heaths.

Vital statistics

Length: 30 mm across forewings

Calendar

Not seen in JanuaryNot seen in FebruaryNot seen in MarchNot seen in AprilSeen in MaySeen in JuneSeen in JulySeen in AugustSeen in SeptemberSeen in OctoberNot seen in NovemberNot seen in December

Key to calendar