Blues

In my experience, it is complicated to distinguish the Blues (Polyommatinae), a subfamily of the Gossamer-wing butterflies (Lycanenidae), if you don’t know which aspects are the essential differences. An important aspect is that the underside of the forewing is white, grey, or light brown (never orange) with black dots or dark stripes. A second important aspect is the presence or absence of a spot at the base of the underside of the forewing. In addition, the presence of a central spot on the top of the wings, whether or not a continuation of orange moon spots on the underside, and the white or checkered fringes play an additional role in the decision for the correct species. For the Common Blue, Brown Argus, and Silver-studded Blue, the distinction can be easily obtained from the underside of the rear wing. The Silver-studded Blue often has a white band along with the moon spots, and the Common Blue and Brown Argus have a white cone (marked blue). The Common Blue has the front three dots in a row, and the Brown Argus like a “hockey stick” (indicated in red).

 

Genus: Agriades

Cranberry Blue – 2024 (CH)
(NCBI-index: 596771)

In the Netherlands, the Cranberry Blue (Agriades optilete) was once a common resident butterfly, but is now only sporadically found in Drenthe and southeast Groningen. In other parts of Europe, you see them much more frequently, such as in Switzerland, where I encountered this blue. The habitat is heathland and raised bog, dry or moist open spaces in forests on acidic soil. The absence of these parameters in the Netherlands probably means that you find these blues hardly. In males, the upperside of the wing is deep violet-blue. The female is brown with a blue dusting on the hindwing, a small eye, and a silver-colored border along the hind edge. On the underside of the hindwing, in the inner edge corner, is a striking, large orange and blue spot. This spot is characteristic of this species. The flight period spans one generation, from June to August, and the wingspan ranges from 23 to 29 mm. Host plant: Lavender Heather, Small Cranberry, Berry, Cowberry, Blueberry and Common Heather. Dutch name: Veenbesblauwtje. Frisian name: –

Flying period:

 

Genus: Agriades

Alpine Blue – 2024 (CH)
(NCBI-index: 689475)

The Latin name of the Alpine Blue (Agriades orbitulus) has been changed several times. It now has the original name again. It is a species that can only be found high in the Alps and was therefore one of the target species of the hike to the snowline. Both sexes can be found in mud pools with other blues or looking for nectar on small legumes. The male is blue on top with black-edged wings, while the female is dark brown with a blue dusting at the wing root. Only the female has a recognisable spot on the forewing that is blue. The key to recognition is the white spots on the underside of the hindwing. The flight period spans one generation, from June to August, and the wingspan ranges from 25 to 30 mm. Host plant: Mountain Milkvetch. Dutch name: Alpenblauwtje. Frisian name: –

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Genus: Aricia

Brown Argus – 2023 (DE)
(NCBI-index: 91739)

In both males and females, the top of the wings of the Brown Argus (Aricia agestis) is brown and never has a blue colour. As a result, the Brown Argus can in any case be distinguished from the female of the Common Blue (Polyommatus icarus). There is usually a whole row of distinctive orange spots along the trailing edge. All Aricia species can be separated from other genera of similar species by the spots on the hindwings on the underside. The two spots in cells 6 and 7 are paired and do not form an arc with the other spots in this line. With this, the distinction with the female of the Silver-studded Blue (Plebejus argus) can be made. The Common Blue has, in addition to the spot in cell 6 that is not placed inwards, a small root spot on the underside of the forewing, which is missing in the Brown Argus. Furthermore, the underside of the wings in the Brown Argus is light brown, while in the other species, it is often grey-blue. The flight period spans two generations, from May to September, and the wingspan ranges from 25 to 31 mm. Host plant: Common Rock-rose and Common Crow-foot. Dutch name: Bruin blauwtje. Frisian name: Brún blaujurkje.

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Genus: Cupido

Small Blue – 2023 (DE)
(NCBI-index: 596548)

The Small Blue (Cupido minimus) has disappeared from the Netherlands as a resident butterfly since 1984, but incidental sightings are still known in the south of Limburg. The upper side of the Small Blue’s wings is brown, and in the male, it is dusted blue at the root. The undersides of the wings are light grey with small black, white-ringed spots arranged in a row in the submarginal area. The black marks in cells 2 and 6 on the underside of the hindwing are placed inwards. It is the only small blue with no orange spots on the underside. The butterfly is also so small that it can hardly be confused with other species. The distinction from other species is very difficult with the females, but the difference can often be seen with the males. In particular, the blue colour and the region where the observation is made play a role. The flight period spans two generations, from late April to mid-August, and the wingspan measures 9-10 mm. Host plant: Kidney Vetch. Dutch name: Dwergblauwtje. Frisian name: Dwerchblaujurkje.

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Genus: Cyaniris

Mazarine Blue – 2023 (DE)
(NCBI-index: 988025)

The Mazarine Blue (Cyaniris semiargus) has not been a permanent butterfly for the Netherlands since 1974. Occasionally, some sightings are known, especially from the south of the country. In general, the Mazarine Blue is much larger than similar species, but this is not always clear in photos and can cause confusion. The upper side of the wings is a deep violet-blue with black edges in the male and brown in the female. The fringes are strikingly white. At the top, the black borders and the white borders are narrow compared to some Plebejus species, which could look similar from above. The underside of the wings is dark grey to brown with even, white-ringed black dots arranged in a row in the submarginal area. The black mark in cell 6 on the underside of the hindwing is placed slightly inward. In other similar species, notably the Small Blue (Cupido minimus) and Osiris Blue (Cupido osiris), this mark creates a sharp angle by being placed much further inward. Blue pollination on the underside of the hindwing can only be seen at the wing root. The flight period spans two generations, from May to early September, and the wingspan ranges from 32 to 38 mm. Host plant: Red Clover. Dutch name: Klaverblauwtje. Frisian name: Klaverblaujurkje.

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Genus: Cacyreus

Geranium Bronze – 2019 (MN)
(NCBI-index: 266946)

A blue butterfly that originally comes from South Africa, but has spread somewhat more widely across Europe, is rarely spotted in the Netherlands: the Geranium Bronze (Cacyreus marshalli). I did not spot this butterfly in the Netherlands, but in Montenegro, where I was on holiday. The underside of the wing is most characteristic. They are marbled brown-white. The hindwing has a small tail at the tornus, and there are also striking spots. The tops of both wings are brown, and the fringes are strong white with dark brown bands. The flight period for the Netherlands is in July and August, and the wingspan is 14-27 mm. Host plant: Geranium and Pelargonium. Dutch name: Geraniumblauwtje. Frisian name: Geraniumblaujurkje.

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Genus: Celastrina

Holly Blue – 2009 (NL)
(NCBI-index: 203782)

The Holly Blue (Celastrina argiolus) is a butterfly that flies around in two or three generations from March to September. It tends to fly high around bushes and trees, whereas other grassland blues usually stay at ground level. This species is fairly easy to recognise. The tops of the males and females are violet-blue, with the males having narrow black wing edges and the females having a broad black wing edge. The underside is white to silver-blue with small black dots, which distinguish them from Common Blue (Polyommatus icarus). The wingspan is 35 mm. Host plant: Holly, Spindle, Ivy, Dogwood, Snowberry, Bramble. Dutch name: Boomblauwtje. Frisian name: Sprakelbeamblaujurkje.

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Genus: Eumedonia

Geranium Argus – 2024 (CH)
(NCBI-index: 282031)

A typical species for the Alps is the Geranium Argus (Eumedonia eumedon). In both males and females, the upperside of the wings is brown, but only in the female are vague orange spots visible on the hindwing along the trailing edge. The fringes are strikingly white. On the underside of the wings, both sexes have orange lunar spots in addition to the black dots. In males, these are less visible. The most striking feature is the white stripe from the black curved central stripe along vein V5 towards the trailing edge. The flight period spans one generation, from May to August, and the wingspan ranges from 26 to 30 mm. Host plant: Wood Cranesbill. Dutch name: Zwart blauwtje. Frisian name: –

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Genus: Hemiargus

Ceraunus Blue – 2024 (MX)
(NCBI-index: 689568)

During a tour through Mexico, a visit to a Mayan site yielded a beautiful new species for the “blue ones”. Stretched out on my stomach, I could photograph the Ceraunus Blue (Hemiargus ceraunus) with some patience. The upper side of the male’s wings is light blue with a thin black wing edge. The female is dark brown, and you see a blue colour at the wing base. The fringes are strikingly white. As with other congeners, identification depends on the pattern on the underside of the wings. Depending on the region, the colour on the underside varies, as does the number of eye-catching black spots. In the west, the colour is more grey, and one black spot is visible along the trailing edge of the hindwing. In the species in the east, the underside is more brown, and you can see two large black spots along the rear edge. In both species, two black spots can be seen along the leading edge of the hindwing, and the underside of both wings consists of a pattern of brown spots and stripes. The flying period is most of the year, and the wingspan is 20-30 mm. Host plant: Partridge Pea, Rosary Pea. Dutch name: Ceraunusblauwtje. Frisian name: –

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Genus: Lampides

Long-tailed Blue – 2007 (FR)
(NCBI-index: 228011)

The Long-tailed Blue (Lampides boeticus) is a butterfly that occurs mainly in southern Europe in several generations from March to September. The butterfly gets its name from the wispy ‘tails’ on the dorsum of each of its hind wings, which flutter in the breeze. The underside of the hindwing has a clear white band in the marginal area and numerous narrow white lines. On the top near the base, a prominent black spot and one next to it at the inner edge corner could be seen. With these spots, they fool birds into thinking this is the head of the butterfly, allowing it to escape any attacks unharmed. Males are more violet-blue, and females have a mix of duller blue and brown. The underside of both sexes is sandy brown, crossed by numerous white, wavy lines. The wingspan is 32-42 mm. Host plant: Bladder-senna, Broad-leaved Everlasting-pea, Broom. Dutch name: Tijgerblauwtje. Frisian name: Tigerblaujurkje.

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Genus: Leptotes

Lang’s Short-tailed Blue – 2010 (FR)
(NCBI-index: 282318)

A variant of the Long-tailed Blue (Lampides boeticus) is the Lang’s Short-tailed Blue (Leptotes pirithous). This butterfly flies in several generations from March to October, typically only in Southern Europe. The underside of the hindwing is brownish grey with irregular white lines and without the clear white band like the Long-tailed Blue. The top of the male is purplish-blue, while the female is blue with broad brown edges and dark brown spots. The wingspan is 26-34 mm. Host plant: Rosemary, Gorse. Dutch name: Klein tijgerblauwtje. Frisian name: Lyts tigerblaujurkje.

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Genus: Leptotes

Cassius Blue – 2017 (CO)
(NCBI-index: 1479067)

The Cassius Blue (Leptotes cassius) is found in subtropical areas. I spotted this one in Medellín (Colombia). This blue is very similar to his family member, the Lang’s Short-tailed Blue (Leptotes pirithous) found in the Mediterranean. The Latin name “Cassius” means “false”. The Cassius Blue does not have small tails on the hindwing and has two black trailing spots on the bottom of its wing. The Lang’s Short-tailed Blue has an orange band around the two black spots, where there is a lack for the Cassius Blue. Furthermore, a clear white band can be seen just before the moon spots, where brown spots can still be seen with a family member. The male is purple-blue at the top, and the female is white with black-brown edges and spots. The top of the hindwing is mainly white. The wingspan is 20-35 mm. Host plant: Ornamental leadwort, Rattlebox, Hairy Milk Pea. Dutch name: Vals tijgerblauwtje. Frisian name: –

 

Genus: Lysandra

Adonis Blue – 2007 (FR)
(NCBI-index: 138070)

The Adonis Blue (Lysandra bellargus) is a butterfly found mainly in southern and central Europe, flying in two generations from late April to October. The top of the male is shiny sky blue with a very narrow black border. The female has orange moon spots at the top of the wings, which are often chocolate brown with blue pollination. Both sexes have distinctive black lines that enter or cross the white fringes of the wings. The wingspan is 38 mm. Host plant: Horseshoe Vetch. Dutch name: Adonisblauwtje. Frisian name: –

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Genus: Lysandra

Chalk Hill Blue – 2024 (CH)
(NCBI-index: 268709)

A widespread and often common species, the Chalk Hill Blue (Lysandra coridon). It is part of a very complex group of taxa, with overlapping ranges and characters. The considerable variation between individuals complicates identification. The upperside of the male’s wings is light greyish blue with broad black edges. The female is brown and rarely dusted blue, and along the trailing edge of the hindwing is a series of orange spots. The fringe is a white and black checkered design. The underside of the male’s wings is white-grey. In the female, the underside of the forewing is light brown, and that of the hindwing is dark brown. The bottom of both wings has a pattern of black dots, edged in white, with a large white spot on the hindwing. Small orange spots are near the black spots along the trailing edge. The flight period spans one generation, from late June to early October, and the wingspan ranges from 27 to 35 mm. Host plant: Horseshoe Vetch. Dutch name: Bleekblauwtje. Frisian name: –

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Genus: Phengaris

Large Blue – 2024 (CH)
(NCBI-index: 203779)

Most blue butterflies are difficult to recognise, but the Large Blue (Phengaris arion) is an exception. The upper side of the wings of this relatively large blue butterfly is bright, glossy blue with a black-grey border and several large, sharply defined, elongated black spots. In females, the spots are more extensive than in males, and the black border along the wings is wider. The underside of the wings is brownish-grey with large, white-bordered black spots, clear grey-black lunar spots and trailing edge spots. The underside of the hindwing has a metallic green or blue root dusting. The flight period in one generation is from late May to August, and the wingspan is 38-52 mm. Host plant: Thyme, Real Marjoram. Dutch name: Tijmblauwtje. Frisian name: –

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Genus: Plebejus

Silver-studded Blue – 2017 (NL)
(NCBI-index: 242267)

The Silver-studded Blue (Plebejus argus) is a very small blue that often flies around in one generation from May to August. This butterfly is fairly difficult to recognise, with the black spots at the underside of the forewing usually drawn as a kind of question mark. The male is violet-blue at the top with mostly broad, dark edges. Females are brown with a row of red spots. Undersides are brown-grey with black spots, a row of orange spots, and small greenish flecks on the outer margin. There are no root spots on the underside of the front wing. The wingspan is 29-31 mm. Host plant: Heather. Dutch name: Heideblauwtje. Frisian name: Heideblaujurkje.

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Genus: Plebejus

Idas Blue – 2024 (CH)
(NCBI-index: 155166)

The upperside of the wings of the Idas Blue (Plebejus idas) is bright blue with a white fringe in the male. The black edge on the upperside of the male is narrow. In the female, the upperside of the wings is dark brown with sometimes a blue dusting. Along the trailing edge are a few orange spots, and the fringe is light brown. On the underside of the hindwing is an orange band along the trailing edge with black spots that are dusted with silver. There are no root spots on the underside of the forewing. The black spots on the bottom of the wings are large and round and usually not white-ringed; the black V-shaped spots on the inside of the lunar spots are pointed arrow-shaped. The underside of the wings is light brown in the female and greyish with a light brown haze in the male. The flight period spans one generation, from June to August, and the wingspan ranges from 20 to 28 mm. Host plant: Hairy Greenweed, Common Bird’s-foot Trefoil, Crown Vetch. Dutch name: Vals heideblauwtje. Frisian name: –

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Genus: Polyommatus

Common Blue – 2011 (NL)
(NCBI-index: 265386)

One species often mistaken for others is the Common Blue (Polyommatus icarus). This most common blue flies around in one to several generations in the period from April to October. The top is blue in males and brown in females, often with a violet-blue haze. On the underside of the forewing, there are two base spots with which this butterfly can be clearly distinguished from other species. Unlike Adonis Blues (Lysandra bellargus), the dark veins do not extend into white fringes of wing margins. The wingspan is 35 mm. Host plant: Clover. Dutch name: Icarusblauwtje. Frisian name: Ikarusblaujurkje.

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Genus: Polyommatus

Damon Blue – 2024 (CH)
(NCBI-index: 268641)

At first sight of the Damon Blue (Polyommatus damon), I was very surprised and pleased. With the underside of the wings light brown and a clear white stripe on the hindwing, it has a very striking appearance. Usually, the blues males have a grey underside, while the females have a darker brown underside. Both the fore- and hindwings show a clear pattern of black dots. The upperside of the male is bright blue with black veins and a broad, diffuse black band along the rear edge. The female is dark brown. In both sexes, the fringe line is strikingly white. The flight period spans one generation, from mid-July to August, and the wingspan ranges from 20 to 35 mm. Host plant: Esparcette. Dutch name: Witstreepblauwtje. Frisian name: –

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Genus: Polyommatus

Turquoise Blue – 2024 (CH)
(NCBI-index: 265384)

A beautiful butterfly, rarely seen in more than one or two specimens, although not uncommon at medium altitude. Apart from the characteristic and brilliant colour of the upperside of the male, the male Turquoise Blue (Polyommatus dorylas) can be distinguished from many similarly sized Blues by the black margins running inwards along the veins. The underside is also quite variable and striking because of the large black spots on the forewing and the faint, often white, marginal markings with pale orange (more or less) submarginal markings. Each orange spot appears as a triangle with the apex directed towards the postdiscal zone. The female is brown above with orange spots along the trailing edge. The flight period is two generations from May to August, and the wingspan is 25-31 mm. Host plant: Kidney Vetch. Dutch name: Turkooisblauwtje. Frisian name: –

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Genus: Pseudozizeeria

Pale Grass Blue – 2010 (JP)
(NCBI-index: 307098)

The Pale Grass Blue (Pseudozizeeria maha) is a small butterfly that I spotted in Japan and that does not occur in Europe. Very little is known about this butterfly, which is related to the Dark Grass Blue and the African Grass Blue. Host plant: Wood Sorrel. Dutch name: Vale grasblauwtje. Frisian name: –