Birds bathe in water or dust to help keep clean and get relief from irritating fleas and lice. Many songbirds have learnt to use ants to control lice. Formic acid from the ants is thought to kill the pests. Some birds stand on an ants' nest and fluff out their feathers so the ants run over them. Crows and jays actually hold ants in their beaks and rub them on their feathers. Crows even pick up twigs from bonfires or glowing cigarette stubs and use them in the same way.