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common blue   <>   polyommatus icarus   <>   gormán coiteann


© D Hardiman 2005  

Habitat:  The common Blue is widespread and common.  
It is double brooded. 
Larval Food Plant: Bird's-foot-trefoil  Lotus corniculatus
Flight Time:   Mid-May to mid-August/September
Hibernation:   Overwinters as a larva.
The upperwings of the male Common Blue are a pale violet-blue with a silvery-blue colour towards the body.
The upperwings of the female varies from brown to deep violet-blue and have a series of  black-bordered orange cresent shaped marks at the outer margins.
Both sexes have a distinctive clear white fringe. 

The underside of the male is grey with a silvery-blue at the base  which is more marked on the hindwings.  There are a series of  white-ringed black spots followed by a series of  orange spots at the outer margins. There are similar white-bordered black spots and a white-bordered black bar more medially. 

The ground colour of the female's underwings are brown and slightly bolder in colour than the males, often with more well developed orange spots, which are larger and more pronounced.


                                    ©DHardiman                                   ©DHardiman



                                                                                   Life Cycle of  the Common Blue


The small white disc shaped eggs, measuring up to 0.6 mm in diameter, are laid singly on the young terminal
leaflets of Bird's-foot-trefoil and other leguminous food plants,  and hatch in c.9 days.

Common Blue ovum on  Bird's-foot-trefoil, Kells, Co Kilkenny 2001

               © DHardiman 2001


The fairly stout larva measures up to 13 mm in length, tapers towards the extremities and is flattened
towards the sides.  The body is green with a darker green mediodorsal line and whitish lateral stripe below
the level of the white spiracles.  The small glossy head can retract into the body.  The setae are light brown
dorsally and white laterally.  On the upper surface of the 10th segment there is a honey gland.


Common Blue larva

© DHardiman 2001

The larva feeds on its food plant by day and the first generation is fully grown in about 6 weeks and
goes on to pupate.  But those of the second generation  overwinter , probably in their third instar, about
late Septrmber/early October.  They hibernate low down on the stem of the food plant or on leaf  litter.
It is often seen tended by ants who are attracted by its honey-like secretions, a feature seen in other members
of the Lycaenidae family.  Feeding is resumed late March or early April of the following spring.


Pupation of the overwintering larva occurs about April but later in summer for the following generation(s). 
This occurs at the base of the food plant or sometimes on its lower stem under a few strands of silk.  
Some are buried by ants and it may occasionally be seen inside an ant's nest under a stone. 
The pupal stage lasts c. 14 days.

 Common Blue Pupa

                                © DHardiman 2001


The adult is on the wing by mid-May to early July and again in late July to early September and
later for further generations.

 Common Blue mating        © DHardiman 2004



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Hesperidae ] Pieridae ] Lycaenidae ] Nymphalidae ] Satyridae ] Migrants ] .