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 Name | Celastrina argiolus |
| Family Name | Lycaenidae |
| Kingdom | Animalia |
| Genus | Celastrina |
| Habitat | Gardens, towns, parks |
| Range | Scotland, Northern Ireland, England, and Wales |
| Host Plants | Holly in the spring generation, Ivy in the summer brood |
| Butterfly Description | Blue with faint spots on the underside of wings |
| Caterpillar Description | Green, may have parts of pink |
Description and the difference between males and females
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 azure | The upperside is blue with a dusting of white scales, and the underside is chalky white |
| Common blue | Males are bright blue, with a thin black line on wings’ edges; females are darker, peppered with orange spots |
| Spring azure | Iridescent blue, while females display dark blue shades |
| Pea blue | Slightly darker, with orange edges; undersides are filled with blue/brown lines |
| Adonis blue | Iridescent blue, with a thin black line on the wings’ edges; undersides have dark spots on gray background |
| Pale grass blue | Bright 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.
Predators
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.
Joan is a nocturnal person who loves traveling and coffee. She’s also an animal lover (and rescuer) who makes it a point to befriend every animal she meets. Her passion for learning led her to writing about various topics. As someone who is a nature lover, she aims to continue learning about the wonderful creation—especially butterflies, and at the same time, share her knowledge here at Butterfly Hobbyist.