Large Tortoiseshell Nymphalis polychloros (Linnaeus 1758 )
Family: Nymphalidae , subgroup Nymphalinae (The Nymphalids or Vanessids)
Photos by Peter Eeles
The Large Tortoiseshell looks very similar to a Small Tortoiseshell, but is much larger and the black or dark central area of the upper wings is replaced with orange-brown. Males and females look alike.
This species is usually a found in woods or along tree-lined roads and tracks where there is a mixture of one of its foodplants plus sallow or blackthorn (Prunus spinosa) for nectaring in early spring. The main foodplant is thought to be wych elm (Ulmus glabra) but many other tree species may be used including other elms, willows, poplars, birches, wild cherry and pear trees.
The Large Tortoiseshell is probably extinct as a resident in Britain though there are occasional sightings. These sightings are probably due to either immigration or deliberate or accidental release. It was more common in Britain in the nineteenth century than the twentieth, but even before it was extinct the population size was very erratic. Nineteenth century populations were concentrated in south east England.
The species covers a large area of Africa up to Northern France and east to the Himalayas but it has declined in Western Europe over last 50 years, especially in Netherlands, Belgium and Northern France and the reasons for this are not clear.
Given that it is declining in the countries nearest to Britain the chance of immigrants is presumably going down. However there were three possible sightings in Yorkshire in 2020, one along the river Aire at Newfield Bridge near Airton, Gargrave and two along the coast.
The Large Tortoiseshell doesn’t breed in the British Isles but overseas there is generally only one brood a year from June to August. The adult hibernates and awakens between February and May.
Eggs are laid April and May in batches of 100 to 200 close together. They’re laid in a sleeve formation around an outer twig anywhere from about 3 metres in height to the top of a tree.
The spiny larvae feed together in the protection of a distinctive communal web. After about four weeks they usually drop to the ground in the fifth instar and seek out trunks, twigs and even fence posts on which to change into pupae that blend colour-wise into their surroundings. The pupal stage lasts about 14 days and emergence is usually in July with adults often going into hibernation shortly after hatching. A few may only aestivate, which means going into a torpor in the hot weather rather than full hibernation, and re-appear for a while in autumn. Hibernation sites are similar in range to other Vanessids and include garden sheds and derelict buildings.
Numbers of this species fluctuate considerably, possibly as a result of parasitic attack at the larval stage.
Photo above by P Simmons
The Large Tortoiseshell is not assessed as a UK BAP species.
There are not enough individuals in Britain for aberrations to be relevant.
With thanks to The Butterflies of Yorkshire edited by Howard M Frost
Catherine Jones 10/11/20