Many visitors often regard New Zealand as a primordial Eden; largely devoid of the deadly creatures that live in warmer climates, like Australia. We happily stroll around barefoot without fear of snake-strike (although I once heard about a reptile catcher being called to a NZ house to catch a python… but that’s a story for another time). Even our native plants seem relatively OK, although there are some exceptions like the tutu (Coriaria arborea), poroporo (Solanum aviculare) and kōwhai (Sophora microphylla) that are poisonous to humans. However, the same can’t be said of the New Zealand Tree Nettle, also known as the Ongaonga (Urtica ferox), probably New Zealand’s most dangerous plant lurking in the bush.

Contents

1. What is the Ongaonga
2. Medical mysteries
3. What happens if you are stung
4. Treatment options
5. Can Ongaonga be useful?
6. Conclusion

What is the Ongaonga?

The ongaonga is native to New Zealand and is a spindly shrub reaching up to three metres high. It has prominent long, arrow-shaped leaves with toothed edges. The leaves, stalks, and stems are covered in frosty white hairs that pack a painful (and sometimes deadly) sting.

It’s widespread across the country, typically growing on forest margins and regenerating wasteland. I have often found Ongaonga growing in patches on the edges of walking tracks and growing amidst feral raspberries.

A medical mystery …

In the summer of 1961, two young hunters were hiking through the Ruahines, a mountain range located in the North Island. Dusk fell and they hurriedly pushed through vegetation, rushing to beat nightfall. To their misfortune, they absently brushed against a large prickly plant, the Ongaonga, which stung them over their bare legs and arms. They felt the hideous effects soon after. One of the men recovered after a few days of blindness and trouble breathing, but the other died hours later in hospital. While fatalities involving the Ongaonga have been rare throughout NZ history, they do happen.

More recently, we might look at the mysterious death of Jason Chase. Chase was a 25-year-old shearer who went missing in December 2002 and later found deceased in the Ruahines without any obvious injuries. After 15 years of speculation about the possible cause, a pathologist concluded that Ongaonga was the likely culprit. 

What happens if you are stung

Upon skin contact, the hairs of the Ongaonga inject a dose of triffydin, a toxin made up of a variety of substances including histamine, 5-hydroxytryptamine, and acetylcholine, which all affect the nervous system. Humans show differential responses depending on their exposure and susceptibility. Stinging can cause induce rashes and inflammation, and more severe cases can cause blindness, convulsions, paralysis and death. Some animals, such as dogs and horses are susceptible, while others like goats and deer appear to eat the plant without ill effects.

treatment options for ongaonga

In minor cases of stinging, the Ministry of Health recommends:

1. Washing the area with soap and water to remove any remaining hairs
2. Apply an ice-pack and take anti-histamines
3. Avoid heat (e.g. hot baths/showers)

More severe symptoms (e.g. blindness, fainting, convulsions) warrant a call to the ambulance and emergency treatment.

Is New Zealand’s most dangerous plant good for anything?

Surprisingly, the ongaonga can be consumed if it’s prepared correctly. After peeling, Māori ate the inner stems occasionally – do not try this at home! This species has also attracted scientific interest for its potential use for relieving chronic pain. While the toxin causes intense initial discomfort, this gives way to local numbness- a feature that might be used in future pain relief medications. 

Final takeaways…

The Ongaonga is probably New Zealand’s most dangerous plant if you’re hiking in the bush. As always, prevention is better than cure. If you happen to be on a nature walk through dense bush, stay vigilant and try to wear clothing that covers your arms and legs (as awful as the scorching summer heat can be). Like the old adage “don’t put your fingers where you can’t see them,” at the very least, do not push through messy thickets of unknown plants. Overall, the case of the Ongaonga is a reminder that it pays to be informed and cautious when wandering the wilderness.