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The genus '''Lonomia''' is a moderate-sized group of fairly cryptic saturniid moths from South America, famous not for the adults, but for their amazingly venomous caterpillars, which are responsible for a few deaths each year, especially in southern Brazil, and the subject of hundreds of published medical studies.
The caterpillars are themselves extremely cryptic, blending in against the bark of trees, where the larvae commonly aggregate. The larvae, like most hemileucines, are covered with urticating hairs, but these caterpillars possess a uniquely potent anticoagulant venom.
A typical envenomation incident involves a person unknowingly leaning against, placing their hand on, or rubbing their arm against a group of these caterpillars that are gathered on the trunk of a tree. The effects of a dose from multiple caterpillars can be dramatic and severe, including massive internal hemorrhaging, kidney failure, and actual destruction of the blood itself (hemolysis). The resulting medical syndrome is sometimes called 'Lonomiasis'.
To date, no one has calculated the LD₅₀ values of ''Lonomia'' venom; the rate of human fatality has been documented as 1.7%, compared to a rate for rattlesnakes at about 1.8%, despite the fact that the amount of venom is only a minute fraction (less than 0.001) of the amount in a snake bite. Accordingly, it seems likely that when measured, the LD₅₀ for ''Lonomia'' venom will be among the lowest for any natural toxin known. As the plants the larvae feed upon are not unusually toxic, they presumably synthesize the toxin directly, but the biochemical pathways used have apparently not yet been documented.
While there are many species in the genus, the most troublesome species is ''Lonomia obliqua'', and it is this species which most of the medical research has centered upon. As anticoagulants have some very beneficial applications (e.g., prevention of life-threatening blood clots), a fair bit of the research is with the intent of deriving some pharmaceutically valuable chemicals.

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References

References

★ American Journal of Tropical Medicine & Hygiene article on hemolytic effects

★ Arocha-Pinango C.L., Guerrero B. (2001) ''Lonomia'' genus caterpillar envenomation: clinical and biological aspects. ''Haemostasis'' '31(3-6)':288-93.

★ Gamborgi G.P., Metcalf E.B., Barros E.J. (2006) Acute renal failure provoked by toxin from caterpillars of the species ''Lonomia obliqua''. ''Toxicon'' '47(1)':68-74.

★ Pinto A.F., Silva K.R., Guimaraes J.A. (2006) Proteases from ''Lonomia obliqua'' venomous secretions: comparison of procoagulant, fibrin(ogen)olytic and amidolytic activities. ''Toxicon'' '47(1)':113-21.

★ Veiga A.B., Ribeiro J.M., Guimaraes J.A., Francischetti I.M. (2005) A catalog for the transcripts from the venomous structures of the caterpillar ''Lonomia obliqua'': identification of the proteins potentially involved in the coagulation disorder and hemorrhagic syndrome. ''Gene'' '355':11-27.