If you have hayfever, you'll know that when the pollen count is high you get congested, your eyes are itchy, and you feel lethargic and miserable. In fact, you don't feel like doing anything at all. This, it turns out, also applies to pollen-suffering criminals. A study published in the Journal of Health Economics has found that when the pollen count is unusually high in large cities, violent crime goes down by a significant amount. "Leveraging daily variation in local pollen counts in 16 US cities, we present novel evidence that violent crime declines by approximately 4 percent on days in which the local pollen count is unusually high," the authors write in the study. "While this might sound like a small behavioral response, it is on par with the change in crime that would be expected to accrue from a 10 percent increase in the size of a city's police force." The team looked at crime levels in cities including Chicago, Georgia, and New York. They found that whilst there was a