Lunacy, Animal Bites, and You

A guest post by Justin Hensley (@EBMGoneWild) of Evidence-Based Medicine Gone Wild.

The word “lunacy” receives its etymology from the belief the moon can cause disorders of the mind.  Multiple things – including crime, crisis incidence, and human aggression – are all positively correlated with the phases of the moon.  It is obvious that the moon affects human behavior, but does it affect other animals?

From 1 January 1997 to 31 December 1999 there were 1621 patients seen at the Bradford Royal Infirmary ambulatory and emergency department with a diagnosis of “bite”. The overwhelming majority of these bites (95.1%) are from dogs, with the rest from cats, horses, and rats in descending order. To break down the 29.530589 day lunar cycle, the authors divided it into 10 periods, 9 with 3 days, and 1 with 2 days. Using that breakdown they were able to get a statistically significant difference in the incidence of animal bites at or about the full moon. 

What to take from this? Well, we can’t determine causation from this study certainly. Is it still human behavior causing increased bites, or are animals also influenced by lunar cycles? Notwithstanding the confidence intervals for the “high period” covering the entirety of their chart, they don’t break down the data for each day of the lunar cycle. Most human behavior differences in the full moon have to do with increased nocturnal light, and this doesn’t apply during the day. No reasons are given for the seemingly arbitrary divisions of the lunar cycle either.

Perhaps “lunacy” is every bit a misnomer as “hysteria”.

“Do animals bite more during a full moon? Retrospective observational analysis”