The emerald ash borer is a wood boring beetle. It does nothing whatsoever to human beings, at least not directly. So how could it be responsible for more than 20,000 deaths in the American Midwest? Find out.

Particles in the lungs are not good for humans. While we can stand up to a few, too many shut down not only our respiratory system but other systems as well — especially the cardiovascular system. That’s why diseases that primarily affect the lungs can also cause the heart to fail. It’s also why a beetle a fraction of the size of a penny, which does not directly harm humans in any way, might be responsible for so many deaths.


The emerald ash borer is an invasive beetle that hit the United States in the 1990s. It proved deadly to ash trees, killing nearly every tree that it infected. The beetle caused problems both in the country and in the city. Midwestern city parks became ugly brown spaces full of dead trees. The parks were also full of something less visible. Trees clear pollutants from the air. Green spaces encourage people to get outside and exercise.

It occurred to researchers at the US Forest Service that a loss of trees might cause an increase in health problems for people in the affected cities. While the experiment would not be ethical, or even possible, to intentionally carry out, the emerald ash borer gave scientists a chance to see how trees health and human health are connected.

The team admitted that there was no way to be certain that the results they returned did reflect the connection between tree health and human health. The report they released states, “It is possible that . . . the results are an artifact of an omitted risk factor that is correlated with the borer or residual confounding.” Still, they believe that they did find a relationship between tree loss and the death rate in humans. The results are astounding. Across 15 Midwestern states, the borer was associated with 6113 lower respiratory system related deaths and 15,080 cardiovascular related deaths. The results were especially dramatic in wealthier areas. The researchers believe that people in richer areas are more likely to go into the park at night, and so reap the benefits of trees more than people in poorer areas.

Image: Benjamin Smith

[Source: The Relationship Between Trees And Human Health, The Man Who Touched His Own Heart]