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The red admiral, Vanessa atalanta, is a fast-flying butterfly of the family Nymphalidae, black with bold red-orange bands and white wingtip spots. It is a strong migrant, and its caterpillars feed on nettles rather than on any rare or protected plant. The species ranges across the Northern Hemisphere, from northern Canada to Guatemala in the west and from Scandinavia and northern Russia south to North Africa and China in the east, and it has also become established on Bermuda, the Azores, the Canary Islands, the Hawaiian Islands and New Zealand. In the British Isles it is both a resident and a migrant.
Identification
The red admiral has a wingspan of 64 to 78 mm, with males running smaller at 64 to 72 mm and females larger at 70 to 78 mm. The upperside is velvety black crossed by a broad orange-red band on each forewing and hindwing, with white spots near the forewing tips; the underside repeats the pattern in more muted, mottled tones that help the butterfly blend in when it rests with its wings closed. The sexes look alike, and the species is usually told apart from similar butterflies by the straight, bright band across the wings rather than by any difference between males and females.
Range and habitat
Outside its core range the red admiral favours moist, open places such as marshes, woodlands, fields and well-watered gardens, from sea level to mountain tops. Because it migrates over long distances, a single journey can take it through habitats as different as subtropical lowlands and tundra. This flexibility, combined with its tolerance of gardens and disturbed ground, is one reason the species turns up across such a wide span of latitude and has colonised several oceanic islands.
Life cycle and host plants
Caterpillars feed on nettles, including the common nettle (Urtica dioica) and other Urtica species, as well as pellitory-of-the-wall (Parietaria) and hops (Humulus); gardeners who leave a nettle patch standing are, in effect, feeding the next generation. The number of broods depends on latitude: a single generation is typical in Canada and the northern United States, two across most of the range, and three in the southern United States, while Britain normally manages only one brood a year.
The species overwinters as an adult, tucked into sheltered spots such as tree hollows, evergreen foliage or outbuildings, while in harsher climates the population is renewed each year mainly by fresh arrivals from the south.
Behaviour and flight period
The red admiral is on the wing from March to November across much of its range, with activity peaking in spring and again in autumn. It is a fidgety, swift flier that changes direction rapidly in the air, and adults feed on a wider range of food than most butterflies, taking fermenting fruit, sap from wounded trees and even bird droppings, as well as nectar from composite flowers such as aster, milkweed and alfalfa. Males are strongly territorial, holding an elliptical patch of ground roughly 4 to 13 m wide and 8 to 24 m long and patrolling its edges up to thirty times an hour; each afternoon a male typically perches in a sunlit spot to wait for passing females, driving off rival males and other intruders by outflying and outmanoeuvring them. In Britain the flight pattern is driven by migration: most migrants arrive in May and June, and numbers peak again with a wave of emergence from mid-August to early October. That two-way traffic, north in spring and south in autumn, is the backbone of the species’ life in the cooler parts of its range, where few individuals could otherwise survive the winter in place.
Conservation
The species is assessed by the IUCN under the category shown in the facts box, taken from its Wikidata record. Its wide range, broad diet and strong powers of dispersal mean it is in no immediate danger; nettles, its main host plant, are common and often considered a weed rather than something that needs protecting.
Similar species
- Painted lady (Vanessa cardui): a close relative in the same genus, orange rather than black-based, and an even longer-distance migrant that reaches almost every continent.
- American lady (Vanessa virginiensis): another Vanessa species, orange and black like the painted lady but with two large eyespots on the underside of each hindwing instead of several small ones.