|“||Flying mammals! What'll those boffins think of next?||”|
Fléchette bats are a kind of fabricated beast. These bats eat metal spikes and "release" them over the enemy. They are used on the Leviathan to destroy leather parts of Clanker machines and injure enemy men. The bats also destroy signal flags to stop ships from communicating. Their name comes from the French word for 'dart', so it is likely that they were first fabricated by a French Darwinist boffin.
The middies are responsible for feeding the bats the spikes before battle. Metal spikes are fed to the bats by putting them inside of the fruit that the bats eat. The bats are controlled by using spotlights to shine on targeted objects, which is directed from the Leviathan's bridge. Fléchette bats are afraid of the color red, so turning the spotlight red causes them to defecate over the enemy. The fléchette bats are used on some of the Clanker aeroplanes that attack the Leviathan over the Swiss alps. They are also used to destroy an enemy gyrothopter and the signal flags of the German ships at the beginning of Behemoth.
The bats live in coves on the back of the Leviathan, where, when the ship has a ballast alert, the middies are sometimes sent to attempt to get the bats to fly into the air and lighten the ship.