Interesting Facts About the Common Blue Butterfly

The Common blue butterfly, also known as the European common blue, lives in England and is unique for producing a viscous honeydew-like liquid that ants utilize as food supplies.

Common blue butterfly species summary

Scientific NamePolyommatus icarus
Family NameLycaenidae
HabitatGrassy areas, warm and cool, open or wooded spots
RangeEngland, Ireland, Scotland, and Wales
Host PlantsRestharrow, lesser trefoil, white clover, Lotus corniculatus
Butterfly DescriptionMales have blue wings; females are a bit brown, and undersides are covered in orangey and black spots
Caterpillar DescriptionGreen and thick body

Butterfly Description

Common blue butterfly
Common blue butterfly

The average wingspan of the Common blue butterflies is about 1.5 inches, regardless of gender. Because of this, the Butterfly Conservation Nature Reserves classifies these as small species.

The Common blue butterflies’ wings have varying shades ranging from blue to brown, depending on their location. The males have bright blue dorsal sides, while the females have a combination of brown and blue undertones.

Most Common blue butterflies have absent blue scales on any part of their wings. However, they have even borders of orange markings with dark spots on the center of their forewings (usually found in female butterflies), while their dorsal sides have dark spots on the central region.

Male Common blue butterflies have a paler base shade on their wings. They also usually don’t have distinct orange markings on the upperside of the females’ wings.

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What are their wings made of?

Their wings are mostly made up of microscopic scales that reflect light from different angles. Thus, this structure makes the wings sparkle at times.

Common blue vs. similar blue butterflies

Chalkhill blueBright blue wings, with a spotted line on the wings’ edges, followed by a white ending
Adonis blueIridescent blue, with a thin black line on the wings’ edges; undersides have dark spots on gray background
Holly blueWings are light and bright blue, sometimes with silver streaks scattered throughout the surface
Small blue butterflySomewhat bluish, but mostly darker brown, like some Common blue females
Summer azureThe upperside is blue with a dusting of white scales, and the underside is chalky white
Spring azureIridescent blue, while females display dark blue shades

Caterpillar Description

The thorax and abdomen of the Common blue caterpillar are dirty white and covered with fine hairs as soon as they hatch from their eggs. Their color will change when they molt and proceed to the next instar. Then, they will turn into a leaf-like green, brown, or olive green shade to help them with their camouflage and keep themselves safe from various threats.

What is its preferred habitat?

The Common blue butterflies typically thrive in these habitats:

  • Heathland
  • Woodland clearings
  • Dunes
  • Waste grounds
  • Cool wooded areas
  • Meadows
  • Limestone grassland

Usual Host Plants

The female Common blue butterflies brood and lay their eggs on the larval food plants listed below. These are also where the Common blue caterpillars feed as soon as they hatch from their eggs.

  • Restharrow (Ononis repens)
  • Lesser Trefoil (Trifolium dubium)
  • Greater Bird’s-foot-trefoil (Lotus pedunculatus)
  • Common bird’s-foot-trefoil (Lotus corniculatus)
  • Black Medick (Medicago lupulina)
  • White clover (Trifolium repens)
  • Wildflower (Anthemis arvensisAdonis aestivalis, and other similar species)

What do they eat?

Larvae mostly feed on plants from the bean family. The adult Common blue butterflies get the nectar and other nutritional sources from the following plant species during their entire life cycle:

  • Clovers (Trifolium spp.)
  • Vetches (Vicia spp.)
  • Bird’s-foot-trefoil (Lotus corniculatus)
  • Medicks (Medicago spp.)


The caterpillars consume the underside of the honest plants’ leaves and keep the epidermis (the upper part) intact. As a result, the leaves where they thrive will appear silvery and somewhat translucent.

The male Common blue butterflies are mostly on the go, especially during summer. They will patrol the areas where the host plants are searching for a suitable partner for the breeding season.

Once the breeding season has passed, the female butterflies will work on oviposition and search for the most appropriate food plant to lay their eggs. During this time, they will hover low on the ground to avoid getting the attention of the predators.

Like other butterflies of the other species, the Common blue butterflies do not guard the eggs or look after the hatched larvae.

How do they adapt to cold weather?

Like other similar butterfly species, the Common blue butterflies utilize overwintering to adapt to the cold weather. They will overwinter in the pupal stage, but sometimes as a larva.

They will use the leaf litter around them to protect the chrysalis and lay still on the ground until spring rolls in.

What are some of the common blue butterfly’s predators?

Common blue larvae and butterflies usually avoid these threats:

  • Argus (Argusianus argus)
  • Small mammals
  • Spiders
  • Birds

Their special connection with ants

While they are in hibernation mode, the chrysalis produces a thick liquid that resembles the viscosity of honeydew. The ants consume this liquid and protect the pupa to ensure a stable food supply for themselves.

Where does the common blue butterfly live?

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

Is the species endangered?

There has been a 74% population loss recorded since 1901. This drop could result from the loss of land area, which was covered by Lotus corniculatus — the butterfly’s favorite host plant and main food source. Still, the species keeps the “least concern” status.

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