Scorpions Use Acid and Protons to Make Their Stings More Painful

Scorpions are, like the rest of us, just trying to get by. Although, admittedly, the rest of us don't make highly sophisticated death-juice in our behinds. According to a new study, one species even uses acid to make its sting more painful. Scientists reported their findings in the journal Science Advances.

Venom is a little word that covers scores of different chemicals with different effects, each evolved to combat a certain type of predator or problem. Some are anticoagulants, which can cause death by blood loss. Some are neurotoxic, causing paralysis. Others cause excruciating pain—a fine deterrent for predators too large to be killed outright.

Scorpions in the Buthidae family make more than 100 different toxins, most of which we still don't understand. One such mysterious substance is a peptide called BmP01. The scientists who discovered this compound quickly figured out that it works by activating a pain pathway in the brain called TRPV1. It's the same one capsaicin uses to deliver a jolt of spice.

What they couldn't figure out was how BmP01 was so potent. Its effects on the brain were far more powerful than they should have been, given the teeny-tiny amount of the toxin a scorpion dispenses.

Something was beefing up BmP01's pain-producing powers.

To find out what it was, scientists combed through the chemistry of the remaining components of Buthidae venom. One quality stood out: The venom was unusually acidic.

The researchers realized that the acid allows the venom to shed protons. Under normal circumstances, a high dose of protons can penetrate a pain pathway's defenses. Here, BmP01 and protons act together to activate the pain receptor, creating a stronger response—and more intense pain—than either could have done alone.

This "one-two punch approach" is a brilliant adaptation, the researchers say.

"Animal toxins delivered in this acidic package must have undergone optimization through evolution to better perform their biological functions," they write. "We suggest that, in addition to using a cocktail of toxins, bimodal activation may represent another general survival strategy used by venomous animals."