Full moons have long been associated with werewolves, vampires and witchcraft, but they could also be linked to a rise in animal abuse.
Britain's RSPCA has released statistics showing a correlation between an increase in reports of abuse and the lunar cycle.
It found an average increase in calls so far this year of around 12pc, or 169 reports, when there has been a full moon.
The highest number of calls during a full moon happened in April, when the RSPCA received 339 more calls - a spike of more than 28pc over the day before.
Staff officer Dermot Murphy said: "We can't explain why this phenomenon occurs, though there are anecdotal reports from emergency services that they also see an increase.
"It could be the fact there is increased light during the full moon so people are more likely to spot an animal in distress, or the legend is true and it really does bring out the darker side of human nature."
The link between full moons and extremes in human behaviour has been identified in past scientific studies.
Prof Michal Zimecki, of the Polish Academy of Sciences, analysed dozens of studies that take lunar activity into account, and argued that a full moon could affect criminal activity.
A three-month study of 1,200 inmates at Armley jail in Leeds in the 1990s found a marked increase in violent incidents during the first and last quarters of each lunar month.