The Red Admiral is a frequent visitor to gardens throughout the British Isles and one of our most well-known butterflies. This butterfly is unmistakable, with the velvety black wings intersected by striking red bands.
This butterfly is primarily a migrant to our shores, although sightings of individuals and immature stages in the first few months of the year, especially in the south of England, mean that this butterfly is now considered resident. This resident population is considered to only be a small fraction of the population seen in the British Isles, which gets topped up every year with migrants arriving in May and June that originate in central Europe. Unfortunately, most individuals are unable to survive our winter, especially in the cooler regions of the British Isles.
The number of adults seen in any one year is therefore dependent on the number of migrants reaching the British Isles and numbers fluctuate as a result. In some years this butterfly can be widespread and common, in others rather local and scarce. This is a widespread species and can be found anywhere in the British Isles, including Orkney and Shetland.
Adults may be seen throughout the year but there is build up in May and June as migrants arrive from the continent. These breed and give rise to the next generation of adults with a peak of emergence between mid-August and early October. There is a single 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.
The adults use a wide variety of nectar sources, including Buddleia, Ivy blossom and Bramble. They are also partial to rotting fruit, such as plums that have fallen from the tree. When resting on the ground or on a tree trunk, the undersides of the adults provide superb camouflage, making them almost invisible as they blend into the background.
Egg-laying females are very easy to spot. The powerful flight is replaced by a slow and deliberate flight as she flits from leaf to leaf of the foodplant, depositing an egg if the leaf is deemed suitable. Egg-laying is typically interspersed with periods of nectaring and resting.
The red band of the forewings showing a white spot. Verity counts this spot in with the white submarginal ones, to make seven in all. He says that it only applies to males since the females usually have it and males do not. This is not so in England.
The main costal white spot of the forewings reduced and somewhat obscured and the two lowest white spots of the apical submarginal chain very much enlarged, the bottom one being more than twice normal size, the two together forming a large squarish white blotch. Beneath this, in the red band, is a small white spot. Hindwings showing a small white spot near the costa slightly inwards from the red band. The red band has no black spots. The original description has not been seen. Various authors give figures, sometimes without the white spot on the hindwings. See Berge's Schmett.pl.53.f.15.
Eggs are laid singly on the upper surface of a leaf of the foodplant and several eggs are often laid in the same nettle patch. They are light green at first, but turn darker as the larva develops. Eggs hatch in about a week.
The larva lives within a tent formed by folding the edges of a leaf together, emerging only to feed. As the larva grows it will form a new tent. The larva of this species is one of the easiest to find in a nettle patch, since its location is given away by a series of tents that are highly-visible to the trained eye. The larva is usually found in the largest of these tents.
The larva has several colour forms, ranging from black, to greenish-brown to a very pale yellowish-green. This stage lasts between 3 and 4 weeks, depending on temperature.
Several leaves are drawn together with silk to form a tent within which the larva pupates. It hangs head-down, attached to the roof of the tent by the cremaster. The head of the pupa is quite blunt - whereas those of closely-related species often have two prominent horns. This stage lasts between 2 and 3 weeks.