Vespertilionidae is a family of bats with members occurring on all Continents except Antarctica. With 407 known species, it is the second largest mammal family (Old World Rats and Mice is the largest family, with over a thousand species). Most of them eat insects which they locate on the wing using ultrasound, but they also make sounds audible to the human ear when they are communicating amongst themselves. Most vesper bats are small, between 3 and 13 centimetres long and weighing 40 to 80 grams.
They live on average about 5 years and are preyed on by birds and snakes. Some of the French species may migrate to take advantage of better weather, and all the European species hibernate. All are protected in France but many species are threatened by habitat destruction.
The one in this photo was flying around our garage in June. It is very dark, with broad wings, large for a vesper bat, so it may be a Barbastelle Barbastella barbastellus (Fr. Barbastelle d'Europe).