Australias Stinging Trees: Please Do Not Pet Them

The leaves on Australia’s giant stinging trees may look soft and fuzzy, but do not touch them! “It’s like having a nail shoved into your flesh,” said one biologist.

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The lore that shrouds Australia’s giant stinging trees, of the genus Dendrocnide, is perhaps as dubious as it is vast. Tales abound of nightmarish encounters with the hypodermic-needle-like hairs of its leaves injecting a toxin that drives men to madness and has prompted horses to hurl themselves off cliffs.

Some of these stories are centuries old and cannot be verified. But as Edward Gilding can attest, these legends contain at least one lick of truth: the absolute agony of being stabbed by the fine, downy hairs that adorn the leaves and stems of Dendrocnide. The trees, which can grow taller than 100 feet, are found throughout the rain forests of eastern Australia, where they are known to torment hikers.

The sting from the trees’ hairs also has immense staying power, doling out anguish in waves for hours or days. Some anecdotes have reported intermittent pain lasting months; a few especially bad stings have even landed people in the hospital.

For most victims, such lingering misery might be incentive enough to shun the plants. But Dr. Gilding and a few like-mindedly masochistic colleagues have instead labored to decipher what gives Dendrocnide its punch.

Dozens of experiments and countless stings later, they have identified some of the ingredients involved. As they report Wednesday in the journal Science Advances, Australia’s stinging trees are packed with a toxin that, when injected, latches onto pain-detecting cells in the recipient and makes them go haywire, locking the afflicted area into the molecular equivalent of an infinite scream.

“So many things induce pain, and so little is known about why,” said Isaac Chiu, a neurobiologist at Harvard University who was not involved in the study. Dr. Chiu noted that the trees’ toxins target a molecule, found on nerve cells, that is “fundamental to mammalian pain,” he said. “If this reveals something that blocks that, it would be really exciting.”

The painful potency of Dendrocnide plants has bedeviled researchers for decades. The trees so often harm people that many their habitats are marked by cautionary signage, warning unwary visitors to “beware the stinging tree.” People who frequent these forests sometimes carry respirators, heavy-duty gloves and a fistful of antihistamines.

But even scientists driven enough to inject themselves with extracts made from the trees’ toxins have not been able to work out the source of the sting, said Irina Vetter, a pain researcher at the University of Queensland and an author on the new study.

Those experiments, which are ethically gray, can no longer be conducted, Dr. Vetter said. But she, Dr. Gilding and their colleagues were still able to separate out the chemical components of the toxin from two Dendrocnide species and create synthetic versions of the compounds in the lab. One very small protein found in both plants made mice lick and nip at the spots where it was injected. Dumped onto nerve cells, the molecule flipped the trigger-happy cells into an “on” position, forcing them to send out a deluge of signals.

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