Two very small butterflies on a leaf, one with wings open and one with wings shut; both look greyish in colour Active

Small Blues. Photo: John Woodruff.

Family: Blues
Size: Small   Wingspan: 24mm

The smallest of our butterflies. Nationally widely spread but not plentiful anywhere. South Dorset is one of its strongholds, but it is still only at all common in particular small areas. Its caterpillar food plant, Kidney Vetch, is not particularly rare, so the butterfly’s comparative rarity may be due to a need for especially sheltered conditions.

Where to see

  • Habitat: To find the butterfly, first find areas where its caterpillar foodplant, Kidney Vetch, grows. This will be in limey or chalky areas, or on the coast in sand dunes and cliffs. The butterfly will be found in particularly sheltered nooks (mainly on south-facing slopes), old quarries and steep embankments where the grass is long enough for the Kidney Vetch to flower, but not so long that it overwhelms it.
  • Caterpillar foodplants: Kidney Vetch
  • Best places: Clubmens Down, Durlston Country Park West, Portland: Broadcroft Butterfly Reserve

Distribution map

Small Blue was recorded from these 1km squares in Dorset (2015-19).

  •     1 record
  •     2-9 records
  •     10+ records
Explore the Atlas to see historical distribution trends for this species.

When to see

May and June are the best months to see Small Blues.

Sightings by month (last 5 years)*

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This year and last*

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What to look for

A very small butterfly: a large adult may have a wingspan of 25mm (1″) – compared to a Red Admiral being about 70mm (2.7″).

There are no markings on the upperwings: they are plain with a white fringe. The male is a smokey black with a dusting of silvery-blue scales near the body. The female is dark brown with no blue. Both sexes have white fringes to their wings.

The underwings are very distinctive: silver-grey with a scattering of small black dots, but no orange markings as will be found in other blues. The markings are similar to those of the Holly Blue, but this is a larger butterfly with a pale blue background to the markings, while the Small Blue has a silver grey background.

The male looks dull silver in flight.

Overwinter stage: Caterpillar

Photo gallery

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*Note: The charts shown on this page are drawn only from casual sightings submitted to this website. Records from this website will be added to a lot more data collected throughout the year and used to compile the five-yearly Butterfly Atlases for Dorset and the UK.