In Victorian times the Large Tortoiseshell was considered widespread and common in woodland in southern England. However, this beautiful insect has since suffered a severe decline and there have been less than 150 records since 1951. This butterfly, whose numbers were always known to fluctuate, is generally considered to be extinct in the British Isles, with any sightings considered to be migrants from the continent or accidental or deliberate releases of captive-bred stock. Several causes of its decline have been suggested - including climate change, parasitism, and the effect of Dutch Elm disease on one of its primary foodplants. The hope, of course, is that this butterfly is able to once again colonise our islands. Although previously found in many parts of England, Wales and Scotland, the greatest concentrations were in the midlands, south and east of England. This species has not been recorded from Ireland. Recent sightings have come from the south coast, in particular from South Devon, South Hampshire, the Isle of Wight and West Sussex.
Adults emerge in July and August and overwinter in this stage, re-emerging in the spring. There is one brood each year.
The chart(s) above have been correlated with the phenology plot below, taken from the UK Butterfly Monitoring Scheme. The blue line gives average counts over the full data set from 1976 to date, and the red line gives the average for the last year.
This butterfly hibernates shortly after emerging from the pupa, finding a hibernation site in log piles or outbuildings. On emerging from hibernation in the spring, the butterfly feeds from Sallow flowers and sap runs and the adults mate soon after emerging. This powerful-flyer is often difficult to see when not feeding, as it can be difficult to approach, taking off at high speed at the least disturbance.
Eggs are laid in a cluster around a terminal twig of the foodplant, usually 3 metres or more above the ground and on the sunny side of the tree. They are yellow when first laid, but turn brown just before hatching. Eggs hatch in about 3 weeks.
The larvae are gregarious in all of their instars, living in a communal web, although they disperse prior to pupation. When disturbed the entire group will jerk in unison, which is clearly designed to deter predators. Early collectors often obtained this species by collecting the conspicuous larval webs and rearing the offspring through. This stage lasts around a month.