Red Admiral

The Red Admiral, Vanessa atalanta

Most people’s favourite butterfly!

Description

The Red Admiral is a large and active butterfly that is very commonly found in gardens, often seen in close association with humans, and is one of the best known species in the UK. It is found in most areas of Hadlow parish, in gardens, in woodlands and along farm footpaths. The males and the females are the same. They give on first impression the appearance of a dark butterfly with obvious orange-red and white flashes.  Closer to, you can see that the fore wing is the one with the black and white patterns towards the outside, but both wings, closer to the body, are primarily brown, edged with orange-red borders.  The overall impression is of a confusing flashing of colours as the butterfly flies, obvious at a distance, perhaps even drawing attention, but potentially distracting and off-putting to a would-be predator. Of particular interest are the small but clear tail flashes, initially an electric blue, but gradually fading, as below.

On the underside, the situation is even more interesting, as the fore wing is brightly coloured with the orange and white flashes, but the rear wing is very well camouflaged, allowing the butterfly now to slip its fore-wings inside its rear wings and hide, particularly, it is alleged, in order to overwinter in sheltered spots. This would be a new pattern of behaviour for the Red Admiral in this country, which used to be said to be an entirely migratory butterfly here, thought never to over-winter in the UK. 

Distribution

The autumn generation of Red Admirals can be found almost anywhere in the parish from July to November, and may often settle on your garden furniture, your clothing or even your body, as they rest between bouts of feeding off sugar sources such as flowers or rotting fruit! You could try to encourage them with rotting fruit, such as apples, plums or perhaps bananas.

Most of these Red Admirals set off according to daylength, temperature and wind speed signals to migrate over to Southern Europe, where they will raise another generation of individuals over the winter period. They use wind speed and temperature signals, together with some aspects of internal compass information to navigate their way across.

Over the winter in the south however it is now thought that at least a few of them stay to hibernate in woods or sheds, and in the spring I think you are most likely to find these, by now rather tatty, over-wintering individuals on paths in Hadlow parish in February and March looking for mates. These numbers will be greater in years with mild winters, and on occasion some of these have been observed mating and laying eggs on young nettles that are surviving the frosts. The resulting caterpillars will pupate and a new generation of these UK resident butterflies will appear in late spring, May and June, joining the larger numbers of migrating Red Admirals from the continent. Evidence of successful over-wintering in the UK has really only appeared in the last decade, but does appear to be a trend, possibly linked to climate change.

In the so-called spring generation, the offspring of these over-winterers are joined, if not swamped, by many new immigrants from the continent, some of whom might be the descendants of the individuals from last year who migrated south in the autumn. It is more than likely that the Red Admirals you see in Hadlow or Golden Green in late spring or summer may have flown here from France, Spain or even perhaps from North Africa! Summer numbers may fluctuate from year to year primarily according to the level of immigration in that particular year.

In the late spring, and in particular the summer and autumn, Red Admirals can be found throughout the UK, even reaching the Northern Isles. Although numbers have dropped in the last ten years, the long term (30 year) trend is still upward. There may then be a southward movement in the autumn, increasing numbers in southern woodlands and gardens at the expense of more northern areas.

In the later autumn, a full scale migration back to the continent starts. This appears to be almost “planned” by the butterflies. There is evidence that on warm days with little wind the butterflies fly off across the land towards the channel and then across it at very low level to reduce the impact of the headwind however slight. When the wind is from the north however the temperature may well be colder, but the butterflies try to fly higher, sometimes circling in thermals, until they reach the higher currents of winds that will carry them south at speed. They probably use some sort of internal compass information to help them navigate. They are thought to be then able to travel the 3,000 km or so to areas such as Catalonia in Spain in a relatively few weeks, averaging perhaps over 80 km a day. There is further parallel evidence from Sweden of autumn migration back to Southern Europe via Denmark, apparently also timed to fit with low intensity southerly winds and warmer temperatures, OR higher intensity northerly winds and cooler temperatures. Interestingly here they appear to know where Denmark is, flying generally to the West to make sure they can get across the Baltic channel.

The Red Admiral is found across a huge area of Europe, Asia and North America. In Europe the butterfly is well known as a continental migrant, moving from the south in the Mediterranean area in the winter, to north in Central/Northern Europe in the summer, and back again every year, having a generation in each area according to the availability of nettles in active growth for caterpillars to eat. The same migratory behaviour appears to occur in North America, coupled with some proportion of hibernation (in Texas). In the Mediterranean areas at least there may also be an “altitudinal migration” where the butterflies have a low altitude generation in the winter and a high altitude generation in the summer. With such an effective migratory strategy it is really rather surprising that the Red Admiral appears to be so effectively pre-adapted for hibernation as well! What a clever butterfly!

Life cycle

As the new immigrants arrive each spring, they lay their eggs (individually rather than in clutches) on nettles. The egg-laying females flutter deliberately over the nettles looking for the best sites.

The eggs are light, then dark green, and last for about a week. The larva folds the leaf over itself with silk, chewing the end of the rolled leaf off, and feeds within the tunnel created. It moves on to a new tunnel every few days. The pupa then dangles from a leaf.

The next generation of adults emerge from July onwards, helping to give the large numbers seen in the UK in autumn, together with some further immigration from the continent.

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Oddities

Like the other Nymphalids, the Peacock, Painted Lady, Small Tortoiseshell and the Comma, the Red Admiral has only four functional legs, the front pair of the six being modified into smaller hair-covered “brush feet”. Here is a close-up of the creamy white pair of brush feet of a Red Admiral. They may be involved in sensory perception:

Photographed in Trosley Country Park, the 17th of July, 2013.

Of the four main Nymphalid species in the UK, all four now feeding primarily on nettles (the Comma historically used to rely primarily on the related foodplant, Hops), two have solitary larvae (The Red Admiral and the Comma) and two have gregarious larvae (The Peacock and the Small Tortoiseshell). The gregarious larvae are able to control their body temperatures and keep themselves warm, above 30C, relatively easily by living in such “clumps”.

Predators and parasites

Apantales type parasitic wasps may be at work on the caterpillars of this species. Sharp chunks taken out of the rear of the wings are generally thought to be due to pecks from birds, major would-be predators of the adult butterflies, as below.

Photographed at Dene Park, Hadlow, the 30th of June, 2019.
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