View photos of the medicinal plant Bouvardia ternifolia [Bouvardia glaberrima] (Smooth bouvardia), profiled in Medicinal Plants of the American Southwest.

A passage from Medicinal Plants of the American Southwest:

Bouvardia’s application to scorpion5 stings is interesting. Both research (mice) and historical usage point to its lessening effect on the venomous symptoms of a sting. One of the more notorious scorpion groups in the Southwest (and Mexico) that Bouvardia has connection to is Centruroides spp. (Bark scorpion). Although usually non life–threatening, its sting is very painful (I can vouch for this), and consists mainly of local nerve hyper–stimulation (spasm and the sensation of shooting electrical pains under the skin). It is postulated that Bouvardia reduces this massive neurotransmitter (principally acetylcholine and a number of catecholamines) surge caused by the scorpion’s venom through an interaction between the plant’s constituents and either the venom or the body’s reaction to the venom (more likely). Secure a tincture–soaked cottonball directly to the sting or apply a fomentation or soak using the tea. Drinking a cup of tea every hour or so until the pain has diminished should further help the situation. A 50/50 combination of Bouvardia and Aristolochia (see Pipevine) can also be applied topically.