To evaluate the theory, Maine built “exclosures” – netted structures constructed of steel poles, cables and netting designed to exclude bats from the corn.  Each of the six exclosures were more than 4,200 square feet in area and 23 feet high. The netting could be slid onto the cables to one end like a shower curtain, enabling them to open the exclosures daily so birds could forage normally, and close them at night to exclude the bats. Paired plots where bats could forage normally provided control plots.

The main pest evaluated was the corn earworm, a moth whose larvae feeds on corn, cotton, tomatoes, and many other crops causing direct damage to yield and also possibly introducing fungal infections into the crops. It is estimated that this insect causes billions of dollars in crop damage every year. Bats are known to feed on this moth, but it was unclear whether they consume enough of the moths to suppress larval populations and damage to crops.

The results:

• Nearly 60 percent more earworm larvae inside the exclosures – protected from the hungry bats – than in the unprotected control areas
• More than 50 percent more corn kernel damage per ear in the corn inside the exclosures.
• The damaging fungal growth associated with pests was significantly higher on the corn inside the exclosures,
• The toxins produced by the fungus were much more concentrated in the corn inside the exclosures. 

“My study provides strong support for the idea that bats provide valuable services to society,” Maine said. “By consuming crop pests, bats have tremendous ecological impacts in crop fields. Based on the difference in crop damage I observed, I estimated that bats provide a service to corn farmers worth about $1 billion globally.” 

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