The nettle is a common species on the sides of roads and paths in Spain. Under that same common name there are two species, Urtica dioica and Urtica urens , they are ruderal species that successfully colonize disturbed land. And whoever has ever touched a nettle without taking the appropriate precautionary measures will have suffered its consequences. A sharp intense itching and stinging, which lasts from a few minutes to several hours, and once felt for the first time, it is difficult to forget.
But nettles are nothing compared to a plant that lives in Australia, Indonesia and the Moluccas. The so-called ‘ gimpi gimpi ‘ or ‘suicide stinger ‘, with the scientific name Dendrocnide moroides .
The same stinging structures of nettle
Although the gimpi gimpi is a tree that can reach 20 meters in height, very different from the small herbaceous nettles on our paths, which rarely exceed a meter, both plants have much in common .
Both belong to the same botanical family, the Urticaceae , and in both cases, the leaves and other parts of the plant have an abundance of hairs called trichomes . These very fine, almost transparent structures are coated with silica mineral , which makes them hard, rigid and, at the same time, brittle. When touching these trichomes, their tips break and their sharp edges cut the skin of the unwary and their content penetrates under pressure into the small wound. They function as a kind of self-injecting hypodermic needle .
The difference in the sting between the two plants lies in the type of substance they inject and, consequently, its effects.
Nettles release a cocktail composed mainly of histamine , which generates the initial sensation of itching, and certain neurotoxins , responsible for prolonging this effect that, with luck, lasts several minutes, although if the sting is of a significant magnitude, it can last up to 12 hours.
In the case of the gimpi gimpi, however, the injected cocktail is significantly different. In its composition, a molecule called moroidin has been found, a highly stable peptide composed of eight amino acids, in combination with potassium ions, which act synergistically. This moroidin and its adjuvants are the most probable cause of the effects of the sting of this tree. In addition, the trichomes of species of the Dendrocnide genus are so tiny that the skin often closes over them before their effect is felt, making them virtually impossible to extract.
How long can the gimpi gimpi sting last?
The effects of the gimpi gimpi sting are very serious. Normally, the sting is not felt at the moment, but, in a few minutes, an itching sensation begins that quickly turns into pain. The sensation intensifies, reaching a peak 20 to 30 minutes after the sting. Some describe it as if the skin is constantly exposed to fire.
In the best of cases, the painful sensation disappears after a few days. But cases have been reported for weeks and even months. The pain has come to cause episodes of fainting; Horse and dog deaths, as well as one human death, have been reported in 1922 in New Guinea.
The stinging hairs of the gimpi gimpi have such a strong effect that respiratory problems have been reported in people who had walked near the trees without touching them, just by inhaling the hairs that a gust of wind had torn from the tree.
Why does the gimpi gimpi have these structures?
As with the defensive structures of other urticaceous plants, the presence of these stinging hairs is a defensive adaptation against pressure from herbivorous animals, especially mammals. There is evidence that shows that plants that suffer a greater number of attacks from these animals produce a greater amount of trichomes on their leaves, and a higher concentration of active ingredients.
Since the synthesis of these structures is costly for the plant, the gimpi gimpi prioritize their presence in those leaves that are more attractive to herbivores —young leaves— or those that are at a lower height, and therefore, are more accessible .
References:
Ensikat, H.-J. et al. 2021. Distribution, Ecology, Chemistry and Toxicology of Plant Stinging Hairs. Toxins , 13 (2), 141. DOI: 10.3390/toxins13020141
Hurley, M. 2000. Growth dynamics and leaf quality of the stinging trees Dendrocnide moroides and Dendrocnide cordifolia (Family Urticaceae) in Australian tropical rainforest: implications for herbivores. Australian Journal of Botany , 48 (2), 191-201. DOI: 10.1071/bt98006
Oliver, F. et al. 1991. Contact urticaria due to the common stinging nettle (Urtica dioica)–histological, ultrastructural and pharmacological studies. Clinical and Experimental Dermatology , 16 (1), 1-7. DOI: 10.1111/j.1365-2230.1991.tb00282.x
Schmitt, C. et al. 2013. Painful Sting After Exposure to Dendrocnide sp: Two Case Reports. Wilderness & Environmental Medicine , 24 (4), 471-473. DOI: 10.1016/j.wem.2013.03.021
