Things of Middle-earth
Description:Although it was not yet very cold [in Mirkwood], they [Thorin Oakenshield's company] tried lighting watch-fires at night, but they soon gave that up. It seemed to bring hundreds and hundreds of eyes all round them, though the creatures, whatever they were, were careful never to let their bodies show in the little flicker of the flames. Worse still it brought thousands of dark-grey and black moths, some nearly as big as your hand, flapping and whirring round their ears. They could not stand that, nor the huge bats, black as a top-hat, either; so they gave up fires and sat at night and dozed in the enormous uncanny darkness.
The Hobbit, Ch 8, Flies and Spiders
'Halt!' cried Gandalf, who appeared suddenly... between the advancing dwarves and the ranks awaiting them. ... 'The Goblins are upon you! ... Behold! the bats are above his army like a sea of locusts.' ...
Soon ... the bat-cloud came, flying lower, over the shoulder of the [Lonely] Mountain, and whirled above them shutting out the light and filling them with dread. ...
Soon actual darkness was coming into a stormy sky; while still the great bats swirled about the heads and ears of elves and men, or fastened vampire-like on the stricken.
The Hobbit, Ch 17, The Clouds Burst
Contributors: Elena Tiriel 5.24.04; added links: ET 5.29.04; added vampire-like: ET 6.20.04