Holly Blue

Celastrina argiolus

The Holly blue is a butterfly that belongs to the lycaenids or blues family and is native to the Palearctic. Source

Where it is now

In the last 8 weeks this insect was recorded 10 times across 2 areas (each area is a 5 degree square).

See the Holly Blue on the live map

Movement and weather

Each season it is first heard regularly where daytime highs are around 12°C (typically 9 to 14°C, from 7 areas). That holds across 20° of latitude, which suggests its timing follows temperature more than the calendar.

Over the weeks it was present in the past year, its centre in Europe ranged from 48°N in April to 63°N in May, about 1,700 km apart.

Arrival dates

The week it was first heard regularly in each region, after at least six weeks away. Dates differ from south to north, so a region has a range.

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Figures are effort corrected and come from automatic sound identification, which makes mistakes. How this is measured and how it compares with human observers.