Learn more about the Holly Blue Butterfly

A Holly blue butterfly, known as the Holly blue, native to Scotland, Northern Ireland, England, and Wales, is a tiny blue butterfly that often feeds on mud puddles and aphid honeydew. It's similar to the Common blue.

Holly blue butterfly species summary

Scientific NameCelastrina argiolus
Family NameLycaenidae
Kingdom Animalia
Genus Celastrina
HabitatGardens, towns, parks
RangeScotland, Northern Ireland, England, and Wales
Host PlantsHolly in the spring generation, Ivy in the summer brood
Butterfly DescriptionBlue with faint spots on the underside of wings
Caterpillar DescriptionGreen, may have parts of pink

Description and the difference between males and females

Female on the left, male on the right
Female on the left, male on the right

The wings of the Holly blue butterflies are light and bright blue, sometimes with silver streaks scattered throughout the surface. One thing that differentiates the males from the females is the black markings that outline the forewings and hindwings.

Females have more defined black borders on the costal areas (the edges of both wings). On the other hand, males have faint black markings in the same areas. These are not even present in some cases.

Second-generation females have broader black markings than first-generation females. The latter also have black border markings on the outer parts of their wings. These are thinner but still defined.

The undersides of their wings are light blue – almost white – and have black speckles all over the ventral part. This is the feature that distinguishes them from other similar butterfly species.

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The average wingspan of Holly blue butterflies is about 1.5 inches (3.8 cm), regardless of gender, meaning this is a tiny butterfly.

Holly blue and comparison to similar species

Summer azureThe upperside is blue with a dusting of white scales, and the underside is chalky white
Common blueMales are bright blue, with a thin black line on wings’ edges; females are darker, peppered with orange spots
Spring azureIridescent blue, while females display dark blue shades
Pea blueSlightly darker, with orange edges; undersides are filled with blue/brown lines
Adonis blueIridescent blue, with a thin black line on the wings’ edges; undersides have dark spots on gray background
Pale grass blueBright inner part of the wings, darker edges, muted undersides with some spots

Holly blue Caterpillar Description

The newly-hatched Holly blue caterpillar is usually green, which helps it hide from its predators. Some larvae may have blotches of pink on any part of their body.

They undergo four instars. By the time they reach their peak maturity, they are already half an inch long. At this point, they are also covered in tiny and velvety hair all over the thorax.

What habitats does Holly blue like?

Holly blue butterflies live in the following habitats:

  • Churchyards
  • Towns
  • Parks
  • Hedgerows
  • Gardens
  • Hedgerows

Usual Host Plants

Female adult butterflies lay their eggs on these host plants:

  • Ivy (Hedera helix)
  • Holly (Ilex aquifolium); larvae prefer the female varieties
  • Bramble (Rubus fruticosus)
  • Heathers (Calluna)
  • Alder buckthorn (Rhamnus frangula)
  • Dogwoods (Cornus spp.)
  • Spindle (Euonymus europaeus)
  • Gorses (Ulex spp.)
  • Snowberries (Symphoricarpos spp.)

What do the Holly blue caterpillars and adults eat?

When larvae hatch from their eggs, they feed on flower buds, leaves, and berries of the food plants. Adult Holly blue butterflies get the nectar, sap, and juices from the following plants and flowers:

  • Brambles (Rubus spp.)
  • Honeydew (Cucumis melo L.)
  • Buttercups (Ranunculus spp.)
  • Bugle (Ajuga reptans)
  • Holly (Ilex spp.)
  • Wild Privet (Ligustrum vulgare)
  • Ivy (Hedera spp.)
  • Water Mint (Mentha aquatica)
  • Thistles (Carduus spp. and Cirsium spp.)

Aside from these plants, adult male butterflies get additional salts, nutrients, and minerals they need for breeding from animal dung and mud puddles. They may also feed on aphid honeydew.

Behavior and overwintering strategy

Holly blue larvae create holes in the food plant flower buds or leaves. Adult butterflies adapt to the winter season through overwintering.

They apply this survival tactic in their pupal stage and create their chrysalis on the ground – unlike other butterfly species that prefer to hang the pupa upside down on the leaves or stems of their host plants.

As soon as Holly blue butterflies emerge from their overwintering spots at the start of the spring season, they will fly high. This contrasts with other butterfly species that hover low toward the ground. They come together to feed on puddles.


Holly blue butterflies have these natural enemies:

  • Ichneumon wasp (Ichneumonidae, Megarhyssa macrurus)
  • Birds (Aves)
  • Common wasp (Listrodromus nycthemerus)
  • Spiders (Araneae)

Where does the Holly blue butterfly live?

There have been sightings of the Holly blue butterflies in Scotland, Northern Ireland, England, and Wales.

Is Holly blue endangered?

The total number of Holly blue butterflies fluctuates from time to time, but it is not an endangered species. One of the major factors contributing to the fluctuation is the presence of wasps that prey on these butterflies.

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