The two trees are Dendrocnide excelsa and Dendrocnide moroides. They are common in Queensland, especially on the edges of rainforests and disturbed area. Stinging trees are large canopy trees that may grow up to 40 metres in height, with diameter of up to 4 -5 metres at the base. They are fast growers and consequently act as pioneers in the forest. Their wood is soft and fibrous and even a large tree completely rots away within two years. The leaves of the stinging tree are conspicuous, large, ovate, pale green and often heavily chewed by insects. The flowers are very small, held in open bunches in the forks of the leaves. The fruit is small, nut like and borne on fleshy stalks.
How does the tree sting? The leaves and fruit are covered with tiny silicon hairs, when touched; the silicon hairs penetrate the skin and break off. The hairs are so fine that the skin closes over them and they may be unable to be removed. The hairs also act like tiny hypodermic needles, and release a neurotoxin, and it is the effect of this toxin that produces such excruciating pain. In humans the pain is felt immediately and peaks after about 30 minutes. However since silicon cannot be broken down in the body, and the neurotoxin is activated by touch, heat or cold, the stinging sensation may continue or recur for many months. In addition the toxin is extremely stable, and samples taken 100 years ago can still cause pain.
The stinging tree toxin has some unusual characteristics, most toxins cause physical damage and pain is produced as a symptom, however stinging tree toxin causes intense pain without causing any physical damage.
Stinging trees are related to nettles and like nettles their leaves are nutritious; in fact people traditionally used nettle tea and soup as tonics. It would seem reasonable to suppose that stinging trees developed their sting to protect their leaves, flowers and fruit from being eaten. But stinging trees attract a wide range of native invertebrates, insects, spiders, reptiles, birds and mammals. Insects, possums, pademelons eat their leaves, catbirds and bowerbirds eat the stalks, flying foxes eat the fruit, sooty owls may nest in tree hollows and reptiles forage in the dead stinging leaves on the forest floor. This is another strange characteristic of stinging trees – many native species appear immune to its toxin, while humans and introduced animals are severely effected.
If you are unfortunate enough to be stung, forget the theory about rubbing cunjevoi sap on the sting, it may have a slight cooling effect but it too is actually highly toxic. The best solution is to apply a hair removal wax strip. But better still, look but don’t touch.
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