First aid treatment of the sting from the hydroid Lytocarpus philippinus: the structure of, and in vitro discharge experiments with its nematocysts

Brush contact with colonies of the stinging hydroid Lytocarpus philippinus by divers and snorkellers causes itchy painful weals for which no first aid measures have yet been devised. Laboratory experiments were performed using common household substances to observe whether or not they caused Lytocarpus nematocyst discharge. Fresh and salt water, distilled water, aloe vera and ‘Stingose’ caused no in vitro discharge in nematocysts in situ. Urine and vinegar caused discharge in up to 10% and 15% of polyps per mm² of colony portion, respectively. Methylated spirits caused discharge in all polyps containing mature mastigophores. The results indicate that vinegar (used to inactivate the discharge mechanism of nematocysts in cubozoan stings) activates the discharge mechanism of the nematocysts of this hydroid. Therefore, dousing thoroughly with water to dislodge adhering undischarged nematocyst material, followed by application of ice for pain relief, is advised. This is the same first aid treatment recommended for most non-cubozoan jellyfish stings.