The Large Tortoiseshell (Vanessa Polychloros)
Apart from its larger size, and somewhat different outline, this butterfly may be known from the Small Tortoiseshell by its duller colour, which is brownish-orange; on the fore wing there are, as a rule, no blue crescents in the hind marginal border, but there is an extra black spot placed between veins 1 and 2; on the hind wings a black spot on the front area represents the black basal area seen on the Small Tortoiseshell; and this is an important point of difference, although the two species are not likely to be confused when both are well known. The blue spots referred to as not usually present on the fore wings are stated to occur in specimens emerging from chrysalids that have been kept in a rather cold temperature for a certain length of time.
An aberration known as testudo has the black spots of the fore wings united, and forming blotches on the front and inner areas; the ground colour of the fore wings is lighter, and the hind wings are blacker. This form occurs at large on the Continent, but it is rare; it has also been produced in the course of temperature experiments.
The only eggs of this butterfly that I have been able to obtain are the batch figured on Plate 34. These were purplish with whitish ribs, but no caterpillars hatched from them. Hellins, who squeezed a few eggs from a freshly killed female, states that the colour apparently is a dull green. The ribs vary from seven to nine in number.
The caterpillar in the adult stage is black, with a speckled dark ochreous band traversed by a black central line on the back; the sides are dappled with ochreous grey; the under parts are brown dappled with darker, and merging into the black. The spines are dark ochreous tipped with black, and the head is shiny black and bristly. (The figure is after Buckler.)
These caterpillars live in large companies, often at the top of a high elm tree, from which they may be dislodged by a well-aimed stick, if this happens to be heavy enough to jar the branch when it reaches the mark. Besides elm trees (Ulmus), they also may be found on willow and sallow (Salix), aspen and poplar (Populus), white-beam (Pyrus aria), and various fruit trees, especially cherry. Occasionally they have been found on nettle, but the butterflies from these were small in size. June is the best month for them.
The chrysalis (Plate 34) is greyish, tinged with pink or reddish, sprinkled with greenish, and shaded with brown and black; the back of the body nearest the thorax is adorned with golden spots. I once obtained a number of these chrysalids in July at Mill Hill; they were found suspended by the tail from the edges of boards that formed a rickety old cart-shed standing at one end of a field and beneath an elm tree.
Although this butterfly is often common in the caterpillar state, the perfect insect, which emerges in July and August, is more frequently seen in the spring after hibernation than before that event. It probably establishes itself in suitable quarters, in old trees, faggot stacks, barns, etc., for its long rest during the winter, at an early period after emerging from the chrysalis.
No doubt large numbers are destroyed by their great enemies, the parasitic flies, chiefly perhaps the Hymenopterous Apanteles. An observer states that from fifty chrysalids only one butterfly resulted, all the others were found to be filled with parasites. In another case of one hundred caterpillars, some collected when quite small, only one was not “ichneumoned.”
These butterflies, in common with most other Vanessids, do not pair until the spring, but Barrett cites an instance of caterpillars, from eggs laid by a female in early September, being reared until about 1/2 inch in length, when they apparently laid up for hibernation.
Lanes margined with trees, especially elms, or the verges of woods, are the most likely places in which to find the butterfly. At one time and another it has been observed in nearly every county of England and Wales, and also in some parts of Scotland, but not in Ireland. It appears to be more or less common in all counties around London, extending to Somerset in the west; to Cambs, Norfolk, and Suffolk in the east; and to Northampton and Warwick in the Midlands.
Abroad it is found throughout the greater part of Europe, Asia Minor, and eastward to the Himalayas.