Flittermouse is one of my favourite words. It is a one-time poetic term for a bat. Other similar terms used for the bat included flindermouse, flintymouse and flickermouse. The above flittermouse was photographed by GB.
The German equivalent - Die Fledermaus - was used by Johann Strauss as the title for an operetta that premiered in 1874 and remains part of the regular operetta repertoire today.
The French equivalent is La Chauve-souris - the bald mouse.
A group of bats is called a colony, a cloud or a clowd.