Key to the 'blues' |
Blues can be quite confusing to sort out in the field. A combination of upperside and underside features may be needed for identification of some species. The main confusion occurs between male Common Blue / Silver-studded Blue, female Common Blue / Brown Argus and female Adonis Blue / Chalk Hill Blue. The starting point is to decide whether or not the specimen is Common Blue, which occurs throughout GB and females of which are very variable.
1. Location
· Adonis / Chalk Hill only occur on chalk and limestone downs in S.England
· Silver-studded only occurs on heaths in S.England and E.Anglia
· Large only occurs at a handful of reintroduction sites
· Brown Argus / Northern Brown Argus are most reliably distinguished by location with Northern Brown occurring in Cumbria and Scotland, Brown Argus further south (both species occur in Yorkshire where they may hybridise and may not be reliably separable).
· The only blue ‘blue’ to occur in Scotland is Common
2. Size
· Small – Small Blue (though it does overlap with Silver-studded Blue, Brown Argus and Northern Brown argus)
· Large – Large Blue (only at a known reintroduction site)
· Medium – the rest (but Adonis/Chalk Hill average larger than others)
3. Upperside colour
· Blackish – male Small Blue
· Blue – Common/Holly/Large and male Silver-studded/Adonis/Chalk Hill (Chalk Hill is pale blue, Adonis is bright blue, female Common is a dull blue usually becoming brown towards the wing margin, male Common, Silver-studded & Holly are all violet-blue).
· Brown – Brown & Northern Brown Argus, female Small/Common/Silver-studded/Adonis/Chalk Hill
4. Upperside spots
· Forewing black spots– Large
· Hindwing orange spots – Brown Argus, Northern Brown Argus, female Common/Silver-studded/Adonis/Chalk Hill (these all appear as a subterminal band of orange crescents each just proximal to a more or less distinct black spot)
· Hindwing black spots on a blue wing – Chalk Hill
5. Upperside fringes
· Chequered with black lines reaching the outer fringe margin on all wings – Adonis / Chalk Hill / (Holly? / Brown&Northern Brown Argus)
· Clear white on all wings OR short black marks along the veins at the wing margin which may enter the fringe but do not reach its outer margin – Silver-studded / Common / Large / Small / (Brown&Northern Brown Argus) / (Holly)
6. Upperside black wing margin
· Evenly broad on all wings – Silver-studded / Large
· Evenly narrow on all wings – male Common & Adonis, female Chalk Hill
· Broad on forewing, narrower on hindwing – Holly (when broader in female than male), male Chalk Hill, female Common/Adonis
· Not discernable – Small / Brown&Northern Brown Argus
7. Hindwing underside orange spots
· Absent – Small / Large / Holly
· All others show a subterminal row of orange crescents
8. Underside ground colour
· Dark brown – female Adonis / Chalk Hill
· Grey-brown - Large
· Pale blue – Small / Holly
· The rest are generally pale to mid-brown with more or less blue colour towards the wing bases
9. Specific distinguishing features
· Hindwing underside subterminal black spots with silvery-blue centres – Silver-studded
· Female Adonis vs Chalk Hill: distal border to hindwing upperside subterminal black spots - blue vs white
· Forewing underside with a black spot in basal half of wing = Common vs Silver-studded Blue, Brown and Northern Brown Argus
· Mid-dorsal pair of black spots on hindwing underside in-line = Brown or Northern Brown Argus vs Common in which the more costal spot is more proximally placed.
1. Location
· Adonis / Chalk Hill only occur on chalk and limestone downs in S.England
· Silver-studded only occurs on heaths in S.England and E.Anglia
· Large only occurs at a handful of reintroduction sites
· Brown Argus / Northern Brown Argus are most reliably distinguished by location with Northern Brown occurring in Cumbria and Scotland, Brown Argus further south (both species occur in Yorkshire where they may hybridise and may not be reliably separable).
· The only blue ‘blue’ to occur in Scotland is Common
2. Size
· Small – Small Blue (though it does overlap with Silver-studded Blue, Brown Argus and Northern Brown argus)
· Large – Large Blue (only at a known reintroduction site)
· Medium – the rest (but Adonis/Chalk Hill average larger than others)
3. Upperside colour
· Blackish – male Small Blue
· Blue – Common/Holly/Large and male Silver-studded/Adonis/Chalk Hill (Chalk Hill is pale blue, Adonis is bright blue, female Common is a dull blue usually becoming brown towards the wing margin, male Common, Silver-studded & Holly are all violet-blue).
· Brown – Brown & Northern Brown Argus, female Small/Common/Silver-studded/Adonis/Chalk Hill
4. Upperside spots
· Forewing black spots– Large
· Hindwing orange spots – Brown Argus, Northern Brown Argus, female Common/Silver-studded/Adonis/Chalk Hill (these all appear as a subterminal band of orange crescents each just proximal to a more or less distinct black spot)
· Hindwing black spots on a blue wing – Chalk Hill
5. Upperside fringes
· Chequered with black lines reaching the outer fringe margin on all wings – Adonis / Chalk Hill / (Holly? / Brown&Northern Brown Argus)
· Clear white on all wings OR short black marks along the veins at the wing margin which may enter the fringe but do not reach its outer margin – Silver-studded / Common / Large / Small / (Brown&Northern Brown Argus) / (Holly)
6. Upperside black wing margin
· Evenly broad on all wings – Silver-studded / Large
· Evenly narrow on all wings – male Common & Adonis, female Chalk Hill
· Broad on forewing, narrower on hindwing – Holly (when broader in female than male), male Chalk Hill, female Common/Adonis
· Not discernable – Small / Brown&Northern Brown Argus
7. Hindwing underside orange spots
· Absent – Small / Large / Holly
· All others show a subterminal row of orange crescents
8. Underside ground colour
· Dark brown – female Adonis / Chalk Hill
· Grey-brown - Large
· Pale blue – Small / Holly
· The rest are generally pale to mid-brown with more or less blue colour towards the wing bases
9. Specific distinguishing features
· Hindwing underside subterminal black spots with silvery-blue centres – Silver-studded
· Female Adonis vs Chalk Hill: distal border to hindwing upperside subterminal black spots - blue vs white
· Forewing underside with a black spot in basal half of wing = Common vs Silver-studded Blue, Brown and Northern Brown Argus
· Mid-dorsal pair of black spots on hindwing underside in-line = Brown or Northern Brown Argus vs Common in which the more costal spot is more proximally placed.
Key:
Upperside view:
1. Forewing and hindwing fringes chequered all the way to the edge > Adonis / Chalk Hill
(only found on chalk and limestone downland in S.England)
Males (blue) – turquoise blue with a narrow black margin and no hindwing subterminal black spots = Adonis
- pale blue with a broad black margin and some hindwing subterminal black spots = Chalk Hill
Females (predominantly brown) - Hindwing subterminal black spots bordered distally with blue = Adonis
Hindwing subterminal black spots bordered distally with white = Chalk Hill
2. Fringes clear white or veins marked with a short black line at wing margin not extending to edge of fringe
Holly Blue?
Underside view:
1. No orange spots
2. Ground colour dark brown = Adonis or Chalk Hill (need to see upperside)
3. Silvery-blue centres to subterminal black spots = Silver-studded Blue
4. Forewing with a black spot in basal half; hindwing with mid-dorsal pair of black spots oblique = Common
5. Hindwing with mid-dorsal pair of black spots in-line = Brown / Northern Brown Argus
Upperside view:
1. Forewing and hindwing fringes chequered all the way to the edge > Adonis / Chalk Hill
(only found on chalk and limestone downland in S.England)
Males (blue) – turquoise blue with a narrow black margin and no hindwing subterminal black spots = Adonis
- pale blue with a broad black margin and some hindwing subterminal black spots = Chalk Hill
Females (predominantly brown) - Hindwing subterminal black spots bordered distally with blue = Adonis
Hindwing subterminal black spots bordered distally with white = Chalk Hill
2. Fringes clear white or veins marked with a short black line at wing margin not extending to edge of fringe
- Blackish = male Small
- Blue with narrow black wing margin = Common
- Blue with broad black wing margin = Silver-studded
- Brown without subterminal orange crescents = Small
- Brown with white central forewing spot = Northern Brown Argus (Cumbria and further North) or Brown Argus (South of Cumbria)
- Brown not as above = Common Blue, Brown Argus or Northern Brown (need to see underside)
Holly Blue?
Underside view:
1. No orange spots
- Ground colour pale blue = Holly
- Ground colour pale grey = Small
2. Ground colour dark brown = Adonis or Chalk Hill (need to see upperside)
3. Silvery-blue centres to subterminal black spots = Silver-studded Blue
4. Forewing with a black spot in basal half; hindwing with mid-dorsal pair of black spots oblique = Common
5. Hindwing with mid-dorsal pair of black spots in-line = Brown / Northern Brown Argus