New Zealand red admiral

Description

The red admiral is a medium-sized butterfly with a 50–60 mm wingspan. The top side of the forewings is mostly black, with a central bright red bar running back from the front edge. There are white spots, fringed with light blue, near the forewing tips. The rear wings are a dark reddish brown with a red patch containing four black circles; the centre of each circle is pale blue.

The underside of the rear wings is a mottled collection of white/brown/black shapes, which camouflages the butterfly when at rest. When revealed, the underside of the fore wings display a striking blue eyespot bracketed by white and red arcs.

Distribution and threats

Red admirals are relatively common throughout New Zealand where their food plants occur. Anecdotal evidence suggest their numbers have been declining since the early 1900s, and the species has reportedly disappeared from Auckland. This is linked to the spraying and decline of native nettle plants, although nettle numbers are also affected by drought; nettle species are now being cultivated by NZ Forest & Bird and some councils to be planted as butterfly food. Another factor in red admiral decline has been exotic parasitic wasps. The Australian white-spotted ichneumon wasp Echthromorpha intricatoria is self-introduced, and the pteromalid wasp Pteromalus puparum was introduced by government entomologists in 1932–33 to control the adventive cabbage white butterfly Pieris rapae, a serious agricultural pest in New Zealand. One study at Banks Peninsula noted that 1–19% of red admiral pupae were parasitised by P. puparum, and 20–30% by E. intricatoria.

Life cycle

The primary host plant for red admiral larvae is the native stinging nettle, ongaonga (Urtica ferox), although larvae can also eat other Urtica species. Throughout their life they use the nettle leaf to protect them during the day, by rolling the edge around them, or (as they get bigger) folding the leaf over into a 'tent'.

The green, barrel shaped, ribbed eggs are generally laid singly on a leaf. The larva only eats enough of the eggshell to get out, whereas the closely related yellow admiral larva consumes the whole shell.

Larvae go through 5 growth stages (called instars). For about 10 days they have a brown body with small white spots and fine hairs (setae). At about 2.5 mm they moult and during this stage develop a pale stripe along the body just above the legs. The setae start to develop spikes, usually two or more at this stage. At about 5 mm long they moult again and the pale longitudinal lines become more obvious. At about 10 mm they moult once more, and the setae develop more spikes. The last moult is at about 22 mm, from where caterpillars grow to about 36 mm before pupating into a roughly 20 mm pupa.

It is difficult to tell red admiral and yellow admiral caterpillars apart: looking at the 4th and 6th body segments, the yellow admiral larva has a wider light coloured area than the red admiral. The pupa of the red admiral tends to be thinner and longer than that yellow admiral when compared side by side, but otherwise they are very difficult to distinguish.

Adult red admirals occur most frequently during summer. They over-winter as adults, so can be seen on warm winter days. They are long lived, surviving up to 6 months in the summer, and perhaps 9 months for those which overwinter. The adults feed on nectar from various plant species (native and introduced) and occasionally on seepage of sap. They are strong fliers, but their short flights when feeding and ovipositing are very erratic. Flights over water or mountain ranges are straight and fast, characteristic of a migrating butterfly, but no migration within New Zealand has been reported.