Holly Blue
Celastrina argiolus
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The blue butterfly flying around the tops of hedges rather than down in the grass.
A pale, silvery-blue butterfly whose underside is a clean powder-blue with small black dots and no orange — the easiest way to separate it from a common blue, which has orange crescents beneath. Holly blues fly high around hedges, churchyards, gardens and woodland edge rather than over open grassland, and have spread north into the Dumfries area in recent decades.
Behaviour
It alternates foodplant between generations: the spring brood lays on holly, the summer brood on ivy — one of the neatest life cycles of any British butterfly. Numbers run on a striking multi-year boom-and-bust cycle driven by a parasitic wasp, Listrodromus nycthemerus, that specialises in holly blue caterpillars, so abundant years are reliably followed by scarce ones.
When to see it
Quick facts
- Family
- Blues and coppers (Lycaenidae)
- Wingspan
- 3–3.5 cm
- Status
- Native; spreading north, with boom-and-bust years
Photo by Charles J. Sharp, CC BY-SA 4.0, via Wikimedia Commons