282 
LYCAENIDAE 
of the fore wing, and the short tail of the hind wing of the 
male. The average expanse of the wings is 35 mm. 
(Upper Side.) The ground colour is purplish-bronze-black ; 
there is a fulvous-orange spot at the anal angle of the hind 
wing, and a white line running through the fringe from the 
tail to the anal angle ; the tail is black tipped with white. 
The female is similar, but has no sexual mark on the fore 
wing and the tail is much longer. 
[Under Side.) The under side is fuscous-brown. A waved 
white line crosses the fore wing beyond the middle and 
a straighter one runs across the hind wing, starting near the 
middle of the costa, and before reaching the anal angle it is 
strongly zigzag, forming a complete W. Parallel to the outer 
margin is a series of rich fulvous-orange crescentic markings, 
bordered by fine black crescents along the inner edge; black 
spots border the outer edge. 
Life of Imago. The duration of life of this little butterfly 
is about twenty days. 
Aberration. Aberration in this species is very unusual, 
except for the development of the white markings, which 
in some specimens are very fine ; occasionally the W is alto¬ 
gether missing. 
Genus STRYMON, Hiibner , 1818 
THE BLACK HAIRSTREAK 
Strymon prnni (Linn., 1758). 
(Plate XXIII, facing page 272) 
Of all our indigenous butterflies, the Black Hairstreak is 
probably the rarest, except for the Large Blue and the Mazarine 
Blue, if the latter still exists in Britain, which is doubtful. 
Haunts and Distribution. It is only just over a century since 
S. pruni was first proved to be British, for in that year numbers 
were captured in Monkswood, Huntingdonshire, by a dealer, 
who then disposed of them to a member of the Entomological 
Club. This man thought they were the White Letter Hair¬ 
streak, but later some of the butterflies were obtained by 
