Yale New Haven Hospital mental health worker Vohahnce Barross, is used to dealing with patients who could spin out of control and attack him at a moment’s notice. That doesn’t unsettle him as much as working in the emergency room on a full-moon night. Under Saturday’s full moon-a brilliant “hunter’s moon”- Barross arrived for the night shift braced for trouble. “I knew I would be walking into disaster,” he said. Since the Middle Ages, full moons have been associated in the popular imagination with spooky occurrences: Werewolves. Vampires. The word “lunacy” derives from the bizarre effects that full moons supposedly have on behaviour. In hospitals all over America, doctors and medical staffers-supposedly pragmatic professionals rooted in science-are convinced that full moons are harbingers of chaos in their emergency rooms and delivery wards. Doctors and nurses say a full-moon night, particularly right before Halloween, triggers a flood of admissions, notably among patients suffering psychotic episodes, sporting strange injuries or going into labour under unusual circumstances. Octavia Cannon, an osteopathic OB-GYN in Charlotte, hasn’t forgotten the full-moon night she delivered a “caul baby,” still in its protective membrane after a vaginal delivery. “It looked so spooky, to see the baby in its sac and moving, and you see fluid in there,” Dr Cannon recalls, still rattled by the rare case many years later. She remembers the nurses later saying that the baby, who was healthy, would be imbued with psychic powers. Mary Leblond, an emergency-room nurse at Methodist Hospital in San Antonio, recalls a full-moon night when several school buses raced up to the front of the hospital. The dozens of high-school students packed into the buses had all gotten food poisoning at dinner and were throwing up everywhere. There were so many sick teens that doctors and nurses had to triage on the buses, bringing only the sickest ones inside, Leblond says. “We had people lying on the floor with IVs running,” she says. “It was a funny thing, after the fact, but at the time no one thought it was funny.” Belief in the full-moon effect is so ingrained that some hospitals bulk up on staff-and discourage doctors from taking the day off-to prepare for wild nights. The problem: Multiple scientific studies indicate that doctors’ full-moon superstitions are lunacy. Research shows there is no link between the full moon and hospital admissions. The American Journal of Emergency Medicine published a report in 1996 analysing 150,999 admission records of an emergency department over four years. A full moon occurred 49 times during that period, and not once did it boost admissions. Jean-Luc Margot, a professor of earth, planetary and space sciences at the University of California, Los Angeles, decided to stray from his usual field of study after a good friend who is a midwife regaled him with stories of more births on full-moon nights. Margot set out to determine if the phenomenon was real. He published a paper last year in Nursing Research magazine showing there was “no such correlation” between moon phases and hospital admission rates or birth rates. “It illustrates how intelligent and otherwise reasonable people develop these beliefs that are not founded in reality,” he says, although he concedes he has never spent a full-moon night in a hospital.Strangely, the full moon does cause a “significant increase” in dog and cat visits to emergency veterinary clinics, according to a 2007 study. John Becher, who spent 40 years as an emergency-room doctor in New Jersey and Philadelphia, says any research contradicting the power of full moons is flat-out wrong. On his last full-moon night before he retired in 2012, he recalls, the police brought in two people who were wandering around the city naked, telling passersby, “We’re not ashamed of our bodies. If you’re ashamed of yours, you should cover up. I’ve become a believer to the point where I don’t want to work on a full moon.” The Wall Street Journal decided to investigate during Saturday’s full moon. At Yale New Haven Hospital, home of the nation’s third-busiest emergency department, it was hard to find a doctor or nurse who didn’t believe in the full moon effect or have an explanation for why it occurs. “Our bodies are 70 percent water, and because the moon moves the oceans, it moves the water in your body-people flip out,” says Michelle Schusky, an X-ray technologist who has worked in hospitals for 40 years. After hours of relative calm, however, staffers had to admit that, well, the night was dead.