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Key to Large Blues

Identification: Large Blues

(Large and Alcon Blues)
(Maculinea sp.)

		The key below should help to separate this potentially difficult group:

1		1a) One row of submarginal spots on underside of both forewing and hindwing. A second indistinct row may exist on the hindwing. GOTO 2 1b) Two distinct rows of underside submarginal spots: Large Blue, M. arion. 1c) Complete absence of underside submarginal spots, dark brown ground colour: Dusky Large Blue, M. nausithous.
			1a) one row of submarginal spots. e.g. Mountain Alcon Blue, M. rebeli
			1b) two rows of submarginal spots, Large Blue M. arion
			1c) no submarginal spots, Dusky Large Blue M. nausithous

2		Upperside: 2a) Upperside clear violet blue, no black spots. Male "Alcon type" GOTO 3 2b) Upperside with bright shining blue and clear black spots well separated from the distinct black border. Male Scarce Large Blue, M. teleius. 2c) Upperside black border very broad merging with most of the spots, or completely covering any spots leaving a small basal area of blue. A female - see key below for the underside (2d, 2e). Underside: 2d) Underside forewing fine pale marginal line. "Alcon type" GOTO 3 2e) Underside forewing marginal area uniform ground colour. Scarce Large Blue, M. teleius.
			2a) Clear violet blue, no spots. "Alcon type" e.g. Mountain Alcon Blue, M. rebeli
			2b) Bright blue, spots well separated from black border Scarce Large Blue, M. teleius
			2c) V. broad black border, merging with spots. Female. e.g. Scarce Large Blue, M. teleius.
			2d) Broken white marginal line "Alcon type", e.g. Mountain Alcon Blue, M. rebeli.
			2e) Uniform forewing marginal area. Scarce Large Blue, M. teleius.

3		Differentiating between the two species of "Alcon" Blues may be impossible. Indeed they are probably not different species, rather environmentally induced races. Use of foodplant is probably the most important factor in identification, thus also habitat, altitude and flight time. 3a) Use of Marsh Gentian, Gentiana pneumonanthe, damp habitats, upto around 1000m altitude, flying late July to August. Male with narrow black borders on upperside. Alcon Blue, M. alcon. 3b) Use of Cross Gentian, Gentiana cruciata, dry habitats at low levels, damper at high levels, to above 2000m, end June/ July at lower levels, mid July/August at higher levels. Male with broader black borders on upperside. Mountain Alcon Blue, M. rebeli.
			3a) Egg on Marsh Gentian, Gentiana pneumonanthe Alcon Blue, M.alcon
			3b) Eggs on Cross Gentian, Gentiana cruciata, Mountain Alcon Blue, M. rebeli