Class of 2010 graduate discovers unique population of scorpions


In the summer of 2008, then-third-year PharmD student Daniel Massey was casting about for a topic for his senior research project. He had an interest in venomous animals, so he had been talking with Jude McNally, then managing director of the Arizona Poison and Drug Information Center, about possible topics. They hadn’t decided on anything, they were just tossing ideas around.

Then one day McNally got the news that a child exhibiting all the classic symptoms of a bark scorpion sting had been flown in to University Medical Center. The boy was drooling, agitated, and had uncontrollable jerking of his arms and legs. These symptoms were not uncommon; what was uncommon was that the boy had been stung while visiting a state park in central New Mexico – and bark scorpions were not known to live in that part of New Mexico.

McNally immediately phoned Massey. “Dan,” he said. “I think we’ve got your research project.”

A Surprise Discovery

Many genera of scorpion are found within the United States. The genus Centruroides is distributed throughout the southern half of the country, from California to Florida. The only medically important species within this genus is Centrutoides sculpturatus, or bark scorpion, located primarily in Arizona. At the time the boy from New Mexico arrived at UMC, the bark scorpion had never been documented as occurring that far east of Arizona.

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Forty-eight hours after receiving McNally’s call, Massey was driving to Caballo Lake State Park, New Mexico. With him in his car were his wife, Melanie, an ultraviolet light for detecting scorpions (they are nocturnal creatures and fluoresce under UV light) and locations the boy’s grandmother had provided where she and the boy had been.

Luckily, the woman had also collected the scorpion that stung her grandson. Although it was somewhat crumpled from having been beaten by a shoe, it allowed clinicians in Tucson to positively identify the genus of scorpion as Centruroides. Unfortunately, due to atypical patterns compared to local populations of bark scorpions (C. sculpturatus), the species remained unclear. To positively identify the species, the specimen was sent to a taxonomist at the West Texas A&M University. The results were as McNally and Massey suspected: bark scorpion.

Over the course of two nights in Caballo Lake State Park, Massey collected 111 scorpions.

“They were everywhere,” says Massey. “There is certainly a thriving population of scorpions in New Mexico.”

Learning To Milk

Upon returning to Tucson, Massey discussed his findings with Leslie Boyer, then medical director of the Arizona Poison and Drug Information Center and director of the Venom Immunochemistry, Pharmacology, and Emergency Response (VIPER) Institute. With Boyer’s encouragement, Massey decided to study the New Mexico scorpions by comparing the toxicity of their venom with the toxicity of venom from Arizona bark scorpions. To do this, he had to learn to milk.

“Milking a scorpion is the process of getting it to release its venom into a receptacle such as a capillary tube or a Petri dish,” says Massey. “The danger of being stung doesn’t bother me. I was raised around venomous creatures; I’ve been collecting rattlesnakes and scorpions since I was 8 years old. I like to say I’m a self-taught naturalist.”

Whether or not he’s a naturalist, Massey is now definitely an expert at milking scorpions.  Scorpions release their venom when they are given a mild electrical shock. To administer the shock, Massey picks up a scorpion with a pair of tweezers, then places the creature on a metal tea strainer that has a low voltage current running through it. With his other hand, Massey holds a capillary tube to the tip of the scorpion’s telson – the stinger at the end of the tail – and collects the venom that the scorpion involuntarily excretes.

“At first, I wasn’t very good at it,” says Massey. “Luckily, I ended up dropping only one or two on my lap.”

To get enough venom to study, Massey had to milk 104 scorpions twice, three weeks apart. After being milked, a scorpion needs about three weeks to rebuild its supply of venom.

“They don’t put out much venom at any one time,” says Massey. “They don’t need to; it’s very potent.”

Massey kept the scorpions in plastic food storage containers in the kitchen of his home. He claims Melanie didn’t mind.

“She was interested in the study,” says Massey. “She even helped collect the scorpions.”

In between milkings, Massey fed his little venomous pets crickets.

“I got the crickets at the pet store” he says. “The scorpions liked them; they can chew, you know.”

Once he had collected enough venom to study, Massey hit the road again: this time, to old – not New – Mexico.

The Same -- But Very Different

“I took the venom to Cuernavaca, Mexico, to check toxicities of the venom of scorpions from Arizona and New Mexico. We included scorpions from Mexico in the study as a control group, because Mexican scorpions are known to be more toxic than those from Arizona.”

The most striking result of the tests was that the scorpions found in New Mexico were twice as toxic as those from Arizona. In other words, it would take only about half as much New Mexico scorpion venom as Arizona scorpion venom to create the same symptoms in a person who was stung.

“How could this be?” asks Massey. “The New Mexico scorpions are the same species as the Arizona scorpions. The only difference is that the New Mexico scorpions live in an isolated population. We have a hypothesis: That two or three scorpions with unusually toxic venom were introduced into the New Mexico location, and the new population they created there is more toxic in general. But, as I said, this is just a hypothesis.”

Another interesting finding of the study was that the scorpion antivenom commonly used in Mexico (and made available in Arizona as an investigational drug by the UA’s VIPER Institute) reversed the effects of the New Mexico scorpion venom better than it reversed the effects of Arizona scorpion venom, meaning it required a smaller dosage of antivenom to achieve the same results.

“This is another mystery,” says Massey. “How could antivenom be twice as effective on venom that is twice as toxic? As in all science, answering one question leads to many more. We’ll just have to keep studying.”

He stops for a minute, considering.

“But you know, it’s my passion. It appears my senior project may turn out to be my life’s work.”