A writer in the Entomologist for 1874 mentions Linford Woods, in Bucks, as a locality where he had observed several specimens, mostly females, on flowers of privet.
It is found throughout the greater part of Europe and also in Amurland and Corea.
The White Letter Hairstreak (Thecla w-album).
The male of this butterfly (Plate [94]) is blackish, with a small whitish sex mark at end of the discal cell of the fore wing; there is a small orange spot at the anal angle of the hind wings. The female agrees in colour with the male, but the tails are longer, and there is no sex mark on the fore wings. The under side is brownish, with a white line on each wing, that on the hind wings forming a W before the inner margin; the hind wings have a black-edged orange band on the outer margin which is finely tapered towards the costa. Captured specimens are usually browner than those that are reared from caterpillars.
The species does not exhibit much tendency to variation. The white lines on the under side may be rather broad or very narrow, and that on the hind wings is sometimes so broken up towards the inner margin that the W character disappears; when absence of the anal orange spots on the upper side is associated with the broken line, the form is known as butlerowi. I have several males without the W, and some of these have the orange spot above, whilst others are without it. Barrett refers to a specimen in which there is "on the under side an extension of white colour from the white line towards the margin, in the fore wings forming a broad wedge-shaped band, but in the hind wings occupying the whole space from the white line to the orange band."
The egg has been described as whitish in colour, and in shape something like an orange with a depression on the top. The eggs are laid on twigs of elm in July, and, according to some writers, remain thereon throughout the winter. The caterpillar when full grown is yellowish-green and covered with short hairs; the ridges on the back are yellowish, and there are oblique whitish streaks on each side of the darker dorsal line. The head is black. When about ready to assume the chrysalis state, the whole body becomes purplish-brown. The chrysalis is brownish, sometimes tinged with purple; covered with tiny bristles except on the blackish wing cases, and there are two purplish lines on the back. It is attached by the tail, and has a strand or two of silk around it, generally on the under side of a leaf.
In a state of nature the caterpillar feeds on wych-elm (Ulmus montana), but it will eat the leaves of the common elm (Ulmus campestris). It is to be obtained in May and June by beating wych-elms in localities where the butterfly is known to occur.
The butterfly is on the wing in July, and usually disports itself around the elm trees, but it is fond of bramble blossoms, and may often be netted when feasting on those flowers. It is a local species, but, as a rule, plentiful enough in its localities. It is rare in Hampshire and Dorsetshire, scarce in Sussex, and not found in many parts of Kent. Ripley, in Surrey, was a well-known locality for it in the early part of the last century, and the caterpillars were found there commonly quite recently. In Essex it is generally common near Maldon. And, according to Barrett, it is "plentiful in various parts of Suffolk; very scarce in Norfolk; found more or less plentifully in Herts, Hants., Cambs., and Northamptonshire; very rare in Nottinghamshire; but again to be found in North Lincolnshire; and common in several localities near Doncaster, Barnsley, and elsewhere in Yorkshire. This appears to be its northern limit, and in this respect it contrasts curiously with Thecla betulæ [The Brown Hairstreak], since it extends farther north in the east than that species; yet in the west is recorded no farther than Cheshire and Shropshire, where I found it thirty-five years ago upon Benthall Edge. In Herefordshire it is recorded but rarely; more commonly in Worcestershire; also in Derbyshire and Needwood Forest, Staffordshire; common around Burton-on-Trent and elsewhere in Leicestershire; and in Oxfordshire, Bucks, and Berks. But its metropolis seems to be Wiltshire, where Mr. Perkins has found it around Marlborough and Savernake in thousands, as well as in Gloucestershire." It has also been obtained in Monmouthshire, but its extreme western limit seems to be Weston-super-Mare, Somersetshire. Abroad it is widely distributed in Europe, except the extreme north and south-west; its range extends into Asia Minor, and to Amurland and Japan.