This video from the USA says about itself:
Bats, A Farmer’s Best Friend: Bracken bats on Doppler
21 October 2013
Bats consume millions of insects every night, saving U.S. farmers an estimated $23 billion in reduced pesticide use and reduced insect-caused crop damage. The Bracken Cave Preserve bats consume 100 tons of insects annually.
International Bat Night
The Bat Night takes place every year since 1997 in more than 30 countries on the last full weekend of August.
Nature conservation agencies and NGOs from across Europe pass on information to the public about the way bats live and their needs with presentations, exhibitions and bat walks, often offering the opportunity to listen to bat sounds with the support of ultrasound technology. The general date is set for the last full weekend in August; however, local organisers sometimes choose other dates if more convenient.
The 18th International Bat Night took place on 30-31 August 2014, the 19th International Bat Night will take place on 29-30 August 2015.