The Large Heath Butterfly

The Large Heath Butterfly, Coenonympha tullia, also known as the Common Ringlet and, locally, as the Manchester Argus, is mainly found in wet boggy moorland areas of northern England and Scotland, with a few isolated colonies in Ireland, Wales and Southern England.

They can be found at a few spots in the Northwest; Winmarleigh near Preston, Heysham Moss, where they were re-introduced in 2013, a few scattered locations on the North Yorkshire moors, Foulshaw moss near Milnthorpe in Cumbria, at a couple of sites in the Forest of Bowland and on the Manchester mosses.

Under close observation at the moment due to their vulnerability and status as an indicator species they are on the wing from around June to August and have an erratic flying pattern, flitting low on the moors between the rushy tussocks and clumps of heather.

Identification

This medium-sized butterfly can be very hard to identify, and at first glance can be mistaken for a Meadow Brown or Ringlet, but there are several ways to differentiate it, one is that it always rests with its wings closed, and unlike other butterflies can be seen flying in overcast weather, as long as the ambient air temperature is above 14°C.

Its wingspan is about 3 to 4 cm and they have irregularly-shaped white streaks on the underside of their wings, with 2 to 6 distinct ringed eyespots on the underside of their hindwings. The number and size of these eyespots are one of the things that makes identification difficult and it has been found that there is a strong correlation between the number and size of spots on different forms of the Large Heath and the total of sunshine hours in June and July, when the adults are about and flying.

This has found to be because in summers with more hours of sunshine, or in warmer, southern parts of the country, the adults are much more active and fly more frequently, and this makes them more obvious to attacks by predatory birds, in particular Meadow Pipits, which are also frequently found in the same moorland habitats.

The presence of wing spots in such a situation means that the attacking bird will focus its attention on the eyespots, rather than the body of the insect, therefore, evolutionary process being what it is, this means that these butterflies are more likely to escape being eaten and pass on their genes.

In cooler areas, however, Large Heaths will spend more time perching on the ground or vegetation, so it is advantageous for them to be less, rather than more, conspicuous. So those individuals with less or no spots are more likely to survive. In the north of England there is a happy balance between avoidance and concealment, so there is more of a variation in the appearance of the species here.

Habitat

As the Large Heath is a specialist and very specific to a particular habitat, and doesn’t tend to stray far from its home colony, only up to about 600m, it is classed an an ‘indicator species’, used as an indication of whether there is an improvement or deterioration in the nominal, preferred state of the habitat it is usually found in.

Colonies can be very large, numbering up to 15,000 adults although the majority are much smaller, but these are only found wherever it’s main food plant; Hare’s-tail Cottongrass Eriophorum vaginatum grows, although larvae have occasionally been found on Common Cottongrass, Eriophorum angustifolium, and Jointed Rush, Juncus articulatus, all of which prefer wet, boggy, nutrient poor soils.

The main food source for adult Large Heath butterflies is the nectar of the flowers of Cross-leaved heather, Erica tetralix, and colonies are most often found where the base vegetation layer consists mostly of Sphagnum moss. Larvae also require tussocks of rushes to retreat to in case of predation and if an area is too heavily grazed or burnt, leading to the loss of these tussocks, this can cause the numbers of a colony to drop.

In areas where peatland restoration methods are underway, such as flooding of previously dry areas of moorland, colonies of larval Heath butterflies can be harmed or killed by inundation so it is vital for surveys of indicator species such as the Large Heath to be made prior to such projects being given the go ahead, so as to make sure these projects won’t cause more harm than good to the area.

Lifecycle

The Large Heath lays its eggs singly on the foodplant, preferring dead leaves at the base of thick tussocks. The larvae feed in the daytime from around July to September, go through a period of hibernation overwinter, called a ‘diapause’, and then resume feeding again from March to May, retreating into the tussocks of grass when they are not feeding. Pupation occurs in late May or early June, with the pupae being suspended from the foodplant or nearby vegetation, and emerging as adults when the weather is suitable, but having the ability to suspend the process til the next season if it is not.

Successful reintroduction

Recently Chester Zoo successfully bred and released the Large Heath, locally known as the Manchester Argus, at several sites near Manchester, including Chat Moss on the Greater Manchester Peatlands, where it had been absent for over 150 years, and more reintroduction schemes are currently in the pipeline. Breeding and release is essential to increase numbers of C. tullia because its ability to naturally recolonise is so poor, but these schemes are proving successful so, thanks to their work, this beautiful butterfly’s future is looking very positive.

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