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.