The New Zealand red admiral (Vanessa gonerilla) is a species of butterfly native to New Zealand, where it is relatively widespread. In the Māori language, which is spoken by the people indigenous to New Zealand, the butterfly is referred to as , which means . There are two subspecies of red admiral, which occur on the mainland and on the Chatham Islands, respectively. As an adult, the red admiral has a wingspan of around . The wings are blackish and have distinctive red and white markings. The Chatham Islands subspecies is nearly identical to the mainland subspecies, but has slightly different red markings.
As a caterpillar, it is blackish with various green markings. It is sometimes mistaken for the yellow admiral (Vanessa itea), which is also common in New Zealand. The caterpillar feeds on the leaves of Urtica (stinging nettles), especially Urtica ferox (ongaonga). Egg laying begins in September and proceeds until late May (early spring to late autumn in the Southern Hemisphere). After hatching, it takes five to six weeks for the caterpillar to begin to pupate (develop into an adult), during which it creates a chrysalis (a hard casing) to mature into an adult. After two to three weeks, the adult emerges from the chrysalis. The red admiral is a strong flier that tends to move in an erratic pattern. The Chatham Islands subspecies is reported to be more timid and flighty than the mainland subspecies.
The red admiral was first described in taxonomy in 1775 by Danish zoologist Johan Christian Fabricius from specimens collected during the first voyage of James Cook. It has been proposed that the red admiral is in decline, but this is difficult to assess due to an absence of historical population records. However, under the New Zealand Threat Classification System, it is listed as "Not Threatened". The red admiral is heavily parasitised by the exotic (non-native) wasps Echthromorpha intricatoria (cream-spotted ichneumon) and Pteromalus puparum, which lay eggs in the red admiral pupa. In one survey, P. puparum and E. intricatoria were present in a large number of pupae. It has been suggested that the perceived decline of the red admiral is due to the high level of parasitism by E. intricatoria.
Taxonomy The red admiral was first described in 1775 by Danish zoologist Johan Christian Fabricius as Papilio gonerilla in his taxonomic work Systema entomologiae. The specimens used by Fabricius were collected during the first voyage of James Cook, which was the second time Europeans visited New Zealand, making the red admiral among the earliest species to be formally described in taxonomic literature. The type specimens (the specimens on which the species description is based) are stored in the Banks collection in the Natural History Museum of London. After the species was first described, various authors placed it in the genera Vanessa or Pyrameis, with the species ultimately ending up in the genus Bassaris in 1971 (which was split from Vanessa). After genetic studies in 2005, Bassaris was accepted to be the same as Vanessa and thus the species was moved to this genus. There is a single record of the red admiral creating a hybrid with the yellow admiral (Vanessa itea), a closely related species that is also widespread in New Zealand.
In 1899 German entomologist Johann Dietrich Alfken described the species Pyrameis ida from specimens collected on Chatham Island. The species was named after the collector, Ida Schauinsland, who was visiting the island with her zoologist husband Hugo Schauinsland. The specimens described were thought to be lost, but were eventually rediscovered in 2000. In 1912, the species was designated as a subspecies of the New Zealand red admiral with the mainland population being a separate subspecies.
Naming and etymology The mainland subspecies is commonly referred to as the red admiral or New Zealand red admiral, whereas the Chatham Islands subspecies is referred to as the Chatham Island red admiral. Vanessa gonerilla is also referred to as in the indigenous Māori language. The word is derived from and , which mean "garment" and "red", respectively. The genus name Vanessa is likely derived from the character of the same name in the poem "Cadenus and Vanessa" by Jonathan Swift.
Description
The red admiral has a wingspan of around . The top side of the forewings are mostly black, with a central bright red bar running back from the front edge. There are blue spots and white spots, fringed with light blue, near the forewing tips. The rear wings have a background colour of dark reddish brown with a red patch containing four black circles, with the centre of each circle having a pale blue dot. The extent of brown colouring varies somewhat, with some individuals having a pale brown to near-white background colour at the base of the rear wings and tip of forewings. The underside of the rear wings is a mottled collection of white, brown and black shapes, which camouflages the butterfly when at rest.
The two subspecies of the red admiral are very similar and difficult to distinguish, although the red marking of the hind wing is less extensive in the mainland subspecies than in the Chatham Islands subspecies. The rear margin of the hind wing is also more wavy in the mainland subspecies.
The red admiral is somewhat similar to the yellow admiral (Vanessa itea), which overlaps with it in distribution and is frequently found with it. However, they are easily distinguished by the red-orange markings of the forewing whereas the yellow admiral forewings are distinctly yellowish.
Juvenile stages
The barrel-shaped egg is green and has nine ribs that run from top to bottom up the surface of the egg, which when laid makes the ribs run vertically. Although the adult red admiral is coloured quite differently to the yellow admiral, as caterpillars they are difficult to distinguish. The mature red admiral caterpillar can be distinguished from that of the yellow admiral by the pale pigment markings on abdominal segments four to six, which are somewhat wider in the yellow admiral. The two caterpillars can also be distinguished by the size of setae, hair-like structures, that run along the very top of the abdominal segments and are mounted on thickened stalks. In the red admiral, the uppermost of these setae are shorter than their thickened stalks, whereas in the yellow admiral the same setae are longer than their thickened stalks. The Chatham Islands subspecies has never been described, but is presumed to be identical to the mainland subspecies.During the first instar (developmental stage), the caterpillar is brown with a black head and small white markings scattered throughout its body. During this stage the setae are unbranched. By the end of the first instar, the caterpillar is around in length. The second instar caterpillar is coloured similarly but also has a white stripe above the legs. In this stage the setae are now branched and the caterpillar reaches up to in length. During the third instar, the caterpillar can reach in length, with markings becoming more obvious and the texture of the head being more bumpy. The fourth instar is similar to the third, but with spines of the body now being on raised bumps. In the fifth (final) instar, the caterpillar grows up to in length. Most are black to dark brown on the upper side of the body with light brown and green on the under side. The head is greenish with dark patches. During the pupal stage, the chrysalis (a hard casing covering the developing body) is generally dull brown, with the abdomen being paler than the rest of the body. The surface of the pupa has metallic gold knobs and is highly sculptured. In the last days before completing pupation, the wings are visible through the surface of the pupa.
Distribution and habitat The red admiral is relatively common throughout most of New Zealand, including on Stewart Island. The Chatham Islands subspecies is widespread on Chatham Island and Pitt Island, the second largest island in the group. The species can be found in a variety of habitats, including suburban gardens, forests and on mountains.
Diet
The primary host plant for red admiral caterpillar is the native stinging nettle, also known as (Urtica ferox), although the caterpillar can also eat other Urtica species such as Urtica incisa. In a study where the red admiral was presented with several species of Urtica to lay eggs on, it was found to preferentially lay eggs on Urtica ferox. When the caterpillar was grown on this species, it was generally heavier than when grown on other species, indicating that it was an optimal food source for the caterpillar. This was suggested to be an example of the preference-performance hypothesis, where a species will preferentially lay eggs on plants that are most suitable for the species. The Chatham Islands subspecies is reported to use Urtica australis as a host plant. As an adult, the red admiral feeds on flower nectar from numerous species and on the sap of Nothofagus (southern beech) trees.
Life cycle
Egg laying generally commences in September and proceeds until late May (early spring to late autumn in the Southern Hemisphere). The eggs are typically laid at the tip of the leaves, often on the side with the stinging hairs. The eggs have a low survival rate. In one study in the Canterbury region, the red admiral egg had a mortality rate of around 95%, which was due to parasitism and other factors. After the eggs are laid on their host plant, they will hatch into caterpillars after eight to ten days.
To leave the egg, the caterpillar eats a hole in the top of the egg, but does not eat the rest of the egg. In its host plant, the caterpillar creates a tent-like structure out of a live leaf by bending and pulling the tip of the leaf and fastening it with silk strands. In this tent structure, the caterpillar feeds on the leaf, possibly venturing out at night as well. Due to the host plant's stinging hairs, the caterpillar is extremely safe in the tent. It takes five to six weeks for the caterpillar to develop through its five instars (developmental stages). The caterpillar then pupates (develops into an adult) in the tent, at the stem of the plant or on another solid structure. To do this, it suspends itself from its rear with a strand of silk, then over the course of about a day, it twists its old exoskeleton off, exposing its pupal form. After two to three weeks, the adult red admiral emerges. The adult appears to be most abundant during October. The adult lives for several months, potentially up to a year if it is overwintering.
Based on surveys of egg, caterpillar and adult populations, it appears that the red admiral is multivoltine (producing multiple generations per year) with surveys finding it completes two generations per breeding season, and a third generation may begin (but not be completed) during suitable years. Both during its adult and caterpillar stage, the red admiral during late autumn (the end of their breeding season) tends to be long-lived and will over-winter until the next season. In one multiple year survey, populations were less dense during a low-rainfall season, which may have been because the host plant had lower survival rates. Unlike many other Vanessa butterflies, the red admiral does not migrate.
Behaviour