Whilst recently chasing seabirds on Titi Island we came across tree nettles (ongaonga, Urtica ferox) with super-sized leaves. The largest leaf we measured was 28 cm long, much longer than the maximum leaf length of 18 cm given for this species in the Flora of New Zealand. Perhaps the abundant seabird droppings on this island provide these nitrogen-loving plants with the fertiliser to reach such giant proportions.
Tree nettle only occurs in New Zealand and it packs a nasty punch, as anyone who has brushed into one can attest. The stinging hairs are hollow and inject a number of toxins into the skin when touched. The stings often cause a burning sensation, swelling and numbness, symptoms which can last several days. Tree nettle is known to have killed at least one person, as well as dogs and livestock. Not surprisingly we weren’t keen to test whether the large leaves on Titi Island have a worse sting than normal sized leaves!
However, not everyone avoids tree nettle – it is the favourite food for caterpillars of the New Zealand red admiral butterfly! The caterpillars roll themselves in the leaves to protect themselves from predators.