More red admiral butterflies around … but at a price

OUCH! What a vicious, unfriendly plant to grow in your own backyard. Just brush against the ongaonga or the endemic New Zealand so-called tree nettle (Urtica ferox) and you could be tingling for days. It is a handsome woody shrub, usually found lurking in a damp shady gully on the edge of a forest or patch of scrub. The leaves are long and tapered, with saw-tooth edges bristling with stiff, brittle stinging hairs which also surround the leaf stalks. The tips of these hairs break off when touched releasing a stinging fluid containing histamine and acetylcholine, and other un-analysed components which produce a serious stinging sensation. One person is said to have died from it and there is a good account in Te Ara Encyclopaedia of NZ of a case of poisoning of a hunter, who fortunately survived to tell the story.

Ongaonga Urtica ferox, the New Zealand tree nettle

Despite these scary stories, I am proposing that if more Wellingtonians made the effort to grow this native plant, they would be boosting the local red admiral butterfly population in the same way that rat and possum control has done for tui. That way we would be enhancing endemic New Zealand in our urban environment.

The red admiral butterfly, Vanessa gonerilla, is found only in New Zealand, but other red admirals, all slightly different, occur around the globe, in Europe, North America, Hawaii. South America, India and Australia. All look similar but the New Zealand one stands out due to the iridescent blue centres in the black hindwing spots – like eye-spots. The Australian admiral also lives here and in urban Wellington is much commoner than the red. Easily recognised by its yellow colour-patches it is, naturally, called a yellow admiral. The yellow species (Vanessa itea) seems to fly across the Tasman Sea regularly and, so far as we know, has always been part of the New Zealand fauna as well. It is able to breed in urban New Zealand more successfully than the native one because it utilises a common introduced weedy species of stinging nettle (Urtica urens) which grows in many domestic gardens. For reasons based on its good sense to eat local, the red admiral avoids this urban weed –hence my promotion of the endemic ongaonga.

Red admiral butterfly, Vanessa gonerilla, basking on tree trunk

Red admiral butterfly, Vanessa gonerilla, basking on tree trunk

All admiral butterflies rely on nettles for their caterpillars. The presence of admiral caterpillars is made visible by the way they roll up leaves to form a crude ‘tent’. The tents provide a shield for the caterpillar within, probably to some extent protecting them from the attention of birds. Foliage- eating herbivores like goats, sheep or cattle cannot cope with the stinging hairs of nettles and so avoid eating the leaves, but birds can still decimate red admiral caterpillars when they find them. The caterpillars also get hit from various insect predators and parasites which are not deterred by the concealed feeding places, nor the stinging hairs, so that very few of the initial eggs laid on a nettle will actually survive long enough to become adult butterflies.

Both red and yellow admirals are very strong fliers. Quite a different style from the lazy soaring monarch, the admirals dart and flicker extremely rapidly, usually seen just as flashes of colour until they settle to bask in the sun or feed at a flower. On a fence or tree trunk, they alight facing downwards, then slowly open the wings to receive the warmth of the sun. In this position they are very conspicuous, but also very alert and can almost instantly react to a movement near them by flying away or snapping the wings together to reveal one of the most spectacular examples of insect camouflage. The undersides of admiral wings are mottled brown, grey and black, for all the world like the bark of a tree, and the wing outlines rough and scalloped rendering this large insect almost invisible against the tree trunk. Moreover, its vertical position assures that the wings don’t cast a tell-tale shadow.

Underside of a resting red admiral

Underside of a resting red admiral

The powerful flight of admirals has carried them across the Tasman Sea, to Lord Howe Island (yellow admiral) and throughout the length of New Zealand (red admiral). An admiral butterfly, probably the NZ red admiral, has even been found on an American ice-breaker in the Southern Ocean off the coast of Antarctica, 5,600 km away from New Zealand. I have often seen them in the middle of Wellington Harbour, striking strongly for the other side and they are common on virtually all the offshore islands. It is not surprising then to find red admirals on the Chatham Islands. What is perhaps surprising, given their propensity for going to sea, is that the Chatham Island form has evolved to be slightly different, despite the possibility of intermittent immigration.

Where do red admirals go in the winter? Good question … because different kinds of butterflies have quite different approaches to overwintering. Monarchs fly to certain trees where they mass together for several months; whites spend it being dormant in the pupal stage; our alpine species pass the winter as caterpillars hunkered down in the litter or under rocks to avoid snow and frosts; copper butterflies much the same. But red admirals remain as adult butterflies like the monarch, each one seeking shelter in a crevice or under bark overhangs and lapse into a kind of suspended existence, in which they can fly about on a particularly warm day, or just remain dormant until Spring. The first butterflies out are seen in August, but we are not sure whether they must mate then or are fertilised from the previous autumn and thus set about immediately laying eggs to set up the first generation of the new season.

Ongaonga is not the sort of plant you can buy from your local supermarket or nursery. To grow them, first locate some wild plants (they are quite common in gullies around the Wellington hills) and take some woody cuttings. A dash of rooting hormone should help and a 6-12 month period in potting mix left in a damp shady corner while the roots develop. When new shoots appear they can be planted out. Ongaonga need rich soil, thrive on extra nitrogen; and should be in partial shade with a good supply of moisture (they are usually near streams or seepages). Remember the female butterflies need to locate these leaves so don’t overdo the shade bit. Against a fence and facing south should fulfil these requirements. But also remember that children and unsuspecting adults must be warned of the dangers of touching the leaves!

I look forward to encountering more flashes of red in the Wellington skies during summer.

George Gibbs