D. moroides is notorious for its extremely painful sting which may leave victims suffering for weeks or even months. It is reputed to be the most
urticant plant in Australia, if not the world. After contact with the plant the victim will feel an immediate severe burning and stinging at the site of contact, which then intensifies further over the next 20 to 30 minutes and will last from hours to several days before subsiding. During this time the victim may get little sleep because of the intensity of the pain. In severe cases, it may cause
urticaria (hives), and the
lymph glands under the arms may swell and become painful, and there have been rare cases of hospitalization.
Mechanism Very fine, brittle hairs called
trichomes are loaded with toxins and cover the entire plant; even the slightest touch will embed them in the skin.
Electron micrograph images show that they are similar to a hypodermic needle in being very sharp-pointed and hollow. Additionally, it has been shown that there is a structurally weak point near the tip of the hair, which acts as a pre-set fracture line. When it enters the skin the hair fractures at this point, allowing the contents of the trichome to be injected into the victim's tissues. The trichomes stay in the skin for up to a year, and release the toxin cocktail into the body during triggering events such as touching the affected area, contact with water, or temperature changes. Ernie Rider, a conservation officer with the
Queensland Parks and Wildlife Service, was slapped in the face and torso with the foliage in 1963, and said: For two or three days the pain was almost unbearable; I couldn't work or sleep... I remember it feeling like there were giant hands trying to squash my chest... then it was pretty bad pain for another fortnight or so. The stinging persisted for two years and recurred every time I had a cold shower...There's nothing to rival it; it's ten times worse than anything else. Physical contact with
Dendrocnide moroides is not the only way that it can cause harm to a person—the trichomes are constantly being shed from the plant and may be suspended in the air within its vicinity. They can then be inhaled, which may lead to respiratory complications if a person spends time in close proximity to the plant. The Australian
entomologist and
ecologist Marina Hurley wrote her doctorate studying two
Dendrocnide species of the
Atherton Tablelands, west of
Cairns, namely
Dendrocnide moroides and
Dendrocnide cordifolia, and was exposed to the airborne hairs over a long period of time. She suffered sneezing fits, watery eyes and nose, and eventually developed an allergy that required medical attention.
W. V. MacFarlane, who was a Professorial Fellow in Physiology at the
John Curtin School of Medical Research at the
Australian National University, observed the effects of inhaling the trichomes, and he reported: The plucking of hairs from the leaves invariably produces sneezing in the operator within 10 or 15 minutes. During early attempts to separate stinging hairs from dried leaves, dust and presumably some hairs were inhaled. Initially they produced sneezing, but within three hours there was diffuse
nasopharyngeal pain, and after 26 hours a sensation of an acute sore throat like
tonsillitis was experienced.
Pharmacology The cause of the intense pain has been the subject of scientific research since European explorers first encountered the plant in the mid-19th century. While it is known that a cocktail of toxins is contained within the trichomes, its exact nature was not fully understood . It is known that the active constituents are very stable, since dead leaves found on the forest floor and even decades-old laboratory specimens can still inflict the sting. Early studies suggested that a variety of compounds, such as
histamine,
acetylcholine,
5-hydroxytryptamine and
formic acid, could be responsible; however, none of these has been proven to produce a similar intensity or duration of pain to those exhibited by the sting from the plant. Around 1970 a new compound was identified and given the name
moroidin. It was for a time thought possibly to be the causative agent; however, later research showed that it did not cause the same effects as a sting from the plant. In 2020 a previously unknown family of disulfide-rich peptides was identified by a group of researchers and given the name
gympietides. These compounds were shown to be similar to some toxins found in
cone snails, and produce significant pain responses in laboratory tests. Moreover, their complex structure – resembling the
inhibitor cystine knot – made them highly stable, explaining how the sting lasts for such a long time. There has been anecdotal evidence of some plants having no sting but still possessing the hairs, suggesting a chemical change to the toxin.
Remedies A commonly recommended first-aid treatment is to use depilatory wax or sticky tape to remove the hairs. The
Kuku Yalanji people of
Mossman Gorge used a method that was essentially similar, making a juice from the fruits or roots of the plant and applying it to the affected area, before scraping it off with a mussel shell once it had become sticky. Mechanical removal is not always successful however, as the hairs are so tiny that the skin will often close over them, making removal impossible. Various other treatments, mostly ineffectual, have been tried over time. They include bathing the affected area in hot water, applying papaya ointment, xylocaine or lignocaine cream, and even swabbing with dilute hydrochloric acid. All of these have, at best, a temporary effect. ==Anecdotal stories==