Holly Blue

Holly Blue Celastrina argiolus (Linnaeus 1775)

Family: Lycaenidae, subgroup Polyommatinae (The Blues)


Photo above left by Paul Kipling

Photo above middle Robert Hulmes (and header photo)

Photo above right by CN Cox

The Holly Blue is a small to medium sized blue butterfly. Its shade of lilac-blue is extremely pretty and eye catching. It looks quite similar to the Common Blue from a distance but whereas the Common blue stays close to the ground on open grassland areas, the Holly blue generally flies a bit higher and in more shrubby spots such as by trees in gardens. The underside of the Holly Blue is very different to the Common Blue because it is silvery blue with black dots, unlike the Common Blue’s orange lunules.

The Holly Blue usually perches with wings closed or partially open to about 90°. It is never seen with its wings fully opened. Male Holly Blues have wings which are plain blue on their upper side but females have noticeable black margins to their upper forewings and to a lesser degree, to their upper hindwings. First brood females are less strongly marked than the second brood.

The adults nectar on flowers like buddleia and will also use nutrients from damp mud and animal dung.


This is a species which roams around looking for its foodplants. The main food plants are Holly Ilex aquifolium and Ivy Hedera helix. Therefore the butterfly can be found in gardens, parks and woodland clearings. It is thought that the species mainly uses holly for the spring generation and ivy for the summer but some individuals use other foodplants as well, including dogwoods, gorse, brambles and possibly both alder and common buckthorns.


Overall the Holly Blue is increasing its range north and doing well. It invades from the south in some warmer years, establishing semi-permanent populations, which then often disappear in colder years.

It originally arrived in Yorkshire in 1978 in Nidderdale and around York but then larger invasions happened, firstly in 1990 and then some later years which have led to permanent populations as well. In particular some years see very large invasions to places on the east coast such as South Holderness. These may actually come from Norfolk and head out to sea and back inland to Yorkshire but we don’t yet fully understand the patterns of immigration.

Yorkshire sightings are typically in ones and twos with occasional concentrations on prime sites like York Cemetery Nature Reserve and Haw Park near Wakefield.

The Holly Blue has a range from North Africa to northern England and south Scandinavia and eastward across central Asia to Japan, and North and Central America.

Life Cycle

In the north this species tends to only have one brood but in the south it can have up to three. Adults emerge around the beginning of April to May and if there is a summer brood it emerges from the end of July and lasts until September.

The female lays her eggs at the base of flower buds. The eggs are small but visible, pale discs and they hatch after about two weeks. The larvae then develop through four instars and can appear in at least three forms; most are plain green but some have either purple dorsal and lateral stripes or pink dorsal and lateral stripes. Larvae first eat the flower buds and later the insides of the developing fruit in which they leave a trail of holes.

One unusual feature of the species is that no-one has ever reported seeing the pupal stage in the wild; perhaps because the pupa are high up in trees or shrubs, or low down, possibly underground, where they may be looked after by ants.

The parasitic ichneumon wasp Listrodomus nycthemerus appears to play a major part in the butterfly's life cycle, causing the cyclical boom and bust pattern in its populations. The wasp injects an egg into a first instar larva, which then develops inside the larva without killing its host until it emerges as a wasp from the pupal shell. The Holly Blue spends winter as a pupa and it is assumed that wasp eggs laid on second or third brood larvae also overwinter inside the pupa, which is not killed until just before the wasp emerges the following year. A few days before this event the pupa becomes discoloured in patches.

We know nothing about the success of this wasp in Yorkshire but since the butterfly arrived in 1990 it has gone through the typical population cycles that are known in the south and thought to be associated with the burden of the wasp. The wasp builds up its population with that of the butterfly until the wasp is prolific enough to kill lots of the butterflies and reduce the wasp’s own numbers as a result. The butterfly then breeds again in peace for a few years and build its numbers up again until the wasp catches up and the cycle starts again.

Photo above right of a female laying an egg by Catherine Jones


Butterfly Conservation priority: Low

European status: Not threatened

Fully Protected under the Northern Ireland 1985 Wildlife Order


At least 35 aberrations have been described but it is unusual to see an aberration.

With thanks to The Butterflies of Yorkshire edited by Howard M Frost

Catherine Jones 21/01/20