42 THE GENERA AND SPECIES OF BRITISH BUTTERFLIES. 
Caterpillar (No. 9) feeds on the foliage of the Plum in May, and the perfect insect appears in 
J uly. The Chrysalis (No. 10) is marked with two patches of white, as shown in the illustration. 
This is, comparatively speaking, a new British species, not having been noticed, and Thecla 
IV. album, having been described as 7. Pruni, before Mr. F. Stephens detected the error in 1827 ; 
previous to that time it had evidently been confused with the other species, from which however 
it is very distinct. At Monk’s Wood, and at Overton Wood, Herts, it is sometimes taken in 
abundance, but in other localities it is extremely rare. 
Theela W. album (the Black Hair-Streak, sometimes called the W. Hair-Streak, Nos. 11 to 
14). This pretty species has the upper surface of the wings entirely of a deep full brown, with 
the exception of a small pale speck in the front wings of the male. On the underside (No. 13) 
the white streak forms a strong zigzag towards the posterior angle of the hind wings, from 
which the specific name is derived. The Caterpillar (No. 14) feeds on the Elm and Blackthorn 
towards the end of May or beginning of June, and the perfect insect appears in July. This 
insect, as above remarked, was confused with 7. Pruni previous to the remarks of Mr. Stephens 
on this genus ; Villars and other entomologists having described the two species as identical. 
Previous to its discovery by Mr. Stephens in great abundance, at Ripley, in 1826, where he 
captured two hundred specimens without moving from the spot where he first noticed them, 
the insect was considered rare. Its appearance there in such vast numbers in that season is one 
of the curious entomological facts not easily accounted for, and like the swarm of Vanessa Antiopa 
at Camberwell, and the occasional swarms of Pieris Brassice, it still puzzles our entomologists. 
It has been recently taken at Brighton, Epping, Peterborough, York, and other places, but 
sparingly. 
