The prickly prize of ongaonga

With stems and leaves covered in sharp, needle-like spines, it’s a native plant that screams ‘don’t touch me’.

And rightly so. If you do touch the native tree nettle ongaonga, the consequences can be painful – and even deadly. 

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Walking down the Butterfly Track at Orokonui Ecosanctuary just north of Ōtepoti Dunedin, you’ll come across plentiful ongaonga, purposefully planted.

Why would we want more of this ‘ferocious’ plant that can deliver an unpleasant sting? 

Part of the ecosanctuary's mission is to provide as many native species as possible with habitats and ecosystems, says botanist and educator Taylor Davies-Colley.

“A lot of [pollinator] species require very specific host species for their caterpillars to live on," he tells Our Changing World.

Native butterflies like the kahukura / red admiral rely on the sharp barbs of ongaonga (aka Urtica ferox), which provide a safe haven for their precious eggs and larvae.

As the caterpillar grows, it folds the spiky leaves around itself as a protective tent during the day. 

University of Otago Master’s student Greer Sanger has been researching how the kahukura’s preferences may be leading the butterfly species into an ‘ecological trap’ – a situation where an animal inadvertently opts for a less-than-ideal habitat.

Dragonflies attracted by the shiny surfaces of black headstones because they resemble the surface of water are an example of this.

In the case of kahukura, could introduced nettles be swindling butterflies with the offer of inferior habitat? 

To test this idea out, Sanger caught some kahukura from around Ōtepoti and placed them in special cages with either ongaonga, a Chatham Islands hybrid nettle, or the introduced dwarf nettle. She then watched to see where the butterflies chose to lay their eggs. 

“They definitely had a preference for the native [nettles] over the introduced [species],” Sanger says. “None of them chose to lay on the introduced nettle.” 

The next step of her butterfly-nettle investigations is determining the nutritional quality of different nettle species for hungry kahukura caterpillars. 

In this episode, Claire Concannon hears what it’s like to be stung by ongaonga, meets an exotic parasitoid wasp similar to those threatening kahukura, and learns about experiments to determine the favourite nettle of these beautiful butterflies. 

To learn more:  

• Could ongaonga lead to a new treatment for Guillain-Barré syndrome? Back in 2018, we learnt about the potential medicinal applications of ongaonga under investigation by researchers at the Nelson Marlborough Institute of Technology. 

• Discover more of Orokonui’s conservation work, in this 2021 OCW episode about bringing kākā back to Ōtepoti. 

Thanks to Liz Garton for production help with this episode.