The central rod of the microbasic mastigphore is like a microscopic spear which is impaled, on contact, into the victim by a springy protein. When stung, the pain is absolutely excruciating and the victim usually thrashes around in an attempt to get the sting off, which usually has the opposite effect. The tentacles contract, become sticky and adhere tightly. They remain active for some time, hence attempts at removal may worsen the sting and injure the person attempting to do so. Stung areas have a whipped fiery appearance - erythematous, oedematous lines about 0.5 to 1.0 cm wide wherever the tentacle contacted skin, often with a fine white transverse flecking that looks like frost.
Severe stings result in blackening and necrosis of the affected skin.
Untreated, the pain lasts for days or weeks and healing is poor, usually resulting in permanent scarring. Inactive nematocysts are intact but are prevented from discharging. Contracted tentacle, however, may conceal some active nematocyts, so complete inactivation is not always possible. The administration of methylated spirits causes nematocyst discharge and hence may worsen the sting, and while it will render exposed parts of the tentacle harmless, it is possible for many nematocysts to remain active. Hence vinegar is preferable for first aid.