Why can't Bilbo and the dwarves light a fire in Mirkwood?

Answer 1

They were certainly able to light them. But it wasn't very helpful as these excerpts describe: "It seemed to bring hundreds and hundreds of eyes all round them, though the creatures, . . . Worse still it brought thousands of dark-grey and black moths flapping and whirring round their ears. They could not stand that, nor the huge bats, so they gave up fires"