The upper side is very dark brown, sometimes almost black, and bearing near the _hinder_ edge of the _hind wings_ a _few orange spots_. This character will at once distinguish this from the next species (_W. Album_). On the under side of the hind wing is a _broad band of orange_, having a _row of black spots on its inner edge_.
The _caterpillar_ is green, with four rows of yellow spots. It feeds on the sloe.
The _butterfly_ comes out about the end of June or in July. It is generally a very rare insect, but is occasionally taken in great plenty in certain spots. The Rev. W. Bree, writing to the _Zoologist_ from the neighbourhood of Polebrook, North Hants, says, "_Thecla Pruni_ is very uncertain in its appearance. In 1837 it literally swarmed in Barnwell and Ashton Wolds; I do not scruple to say that it would have been possible { 143} to capture some hundreds of them, had one been so disposed; for the last few years it has appeared very sparingly indeed." It has also been found in the following localities:--Overton Wood; Brington, Huntingdonshire; and Monks Wood, Cambridgeshire.
THE WHITE LETTER HAIR-STREAK. (_Thecla W. Album._)
This is very much like the last in appearance, and has often been mistaken for it by inexperienced eyes. The _points_ of difference are--on the upper side, the absence of the orange band at the hinder edge of the hind wings, and the presence of a _bluish grey circumflex line at the inner angle_; here also is sometimes a _small orange dot_;--beneath, the _orange band forms a series of arches_, bounded on the edge nearest the root of the wing _by a clear black line_ instead of the rounded black spots seen at this part in _Pruni_.
The _caterpillar_, which feeds on the elm, is wood-louse shaped; pea-green, barred with yellow; head black. May be beaten off elm trees in May.
The _butterfly_ appears in July, and is found in various situations, sometimes flying high up round elm trees, sometimes descending to bramble hedges, or fluttering { 144} about in weedy fields a foot or two from the ground. It was formerly a much rarer insect than at present, and now its appearance in any given locality is a matter of much uncertainty. Mr. J. F. Stephens writes as follows to the _Zoologist_:--