Invertebrates
Common Blue
Polyommatus icarus · also called common blue butterfly
On a sunny grass bank, a male common blue opens his wings to show a flash of violet-blue, while nearby a brown female lays an egg on bird’s-foot trefoil and an ant waits to guard the caterpillar.
Overview
The common blue, Polyommatus icarus, is a Least Concern butterfly of flowery grassland across Europe, North Africa, and temperate Asia. Its colourful males, brown females, and partnership with ants make it one of the most familiar and best-studied small butterflies.
A butterfly with ant bodyguards
The sweet secretions of the common blue’s caterpillar pay for an ant escort, a partnership shared by many of the blue butterflies.
Status
Least Concern, widespread and common.
Common Blue: common questions
How can you tell male and female common blues apart?
Males are bright violet-blue above, while females are mostly brown with orange spots and often a dusting of blue.
Why do ants look after common blue caterpillars?
The caterpillars produce sweet secretions that ants feed on, and the ants guard them from predators and parasites in return.
What do common blue caterpillars eat?
They feed on bird's-foot trefoil and other legumes.
Where is the common blue found?
It lives in flowery grassland, dunes, and open ground across Europe, North Africa, and temperate Asia.