Large tortoiseshell butterfly

The large tortoiseshell (Nymphalis polychloros) is fairly common throughout most of Europe, and is also found in north Africa, Asia Minor and as far east as the Himalayas. It is, however, extremely rare in the British Isles, being restricted to southern England and Wales, in very small numbers, and completely absent from Ireland. Indeed, the number of recorded sightings over the last 50 years in the UK has not exceeded 200, and many of those were probably accidental migrants blown in from continental Europe.

There may be several reasons for the decline of this species, which was regarded by the Victorians as being a common butterfly. One cause is doubtless the virtual extinction of the English elm, due to Dutch elm disease, as this is one of the standard food plants for the large tortoiseshell.

The large tortoiseshell lives in woods, parks and cemeteries, and can be seen sucking sap from damaged birch, oak and fruit trees. It is found at altitudes from sea level up to about 1500 metres.

The effects of high and low temperatures on the chrysalides have produced sub-species, notably Nymphalis polychloros erythromelas, found in mountainous areas of north Africa where it flies at altitudes up to 1800 metres. The sub-species may be difficult to identify because of its different wing markings.

The wingspan of the large tortoiseshell is 50-63mm. The forewings are orange-brown with black markings, rounded in the centre and more elongated at the leading edge. The hindwings are orange-brown with fewer markings, and paler nearer the body. The scalloped wing margins are well-defined, with a line of small blue crescents on the hindwings only. The underwings are darker towards the base with an irregular blue-grey marginal band.  The hair covering the legs is very dark brown or black. There are no noticeable differences in markings as between the sexes.

Eggs are laid after the female large tortoiseshells emerge from hibernation, the eggs being red-brown and barrel-shaped. When they first emerge, after about three weeks, the caterpillars stay together on their food plants, which are elm, willow, poplar and fruit trees. As they prepare to pupate, which they do beneath leaves of the food plant, the caterpillars move apart.

The pupal stage lasts for two to three weeks, with the imagos flying from June or July before hibernating over the winter. Large tortoiseshells are often seen together with Camberwell Beauties, as they have similar ways of life and seasonal habits.

© John Welford