Bewitched!

Winter is the season to spot these curious clumps of tangled twigs among the birch branches. They're often mistaken for birds' nest but in fact they are galls, abnormal growths caused, in this case, by a parasitic fungus Taphrina betulina. The tree responds to the fungal attack by producing these twiggy tufts. They're known as Witches' Brooms and were once thought to be caused by witches flying over the trees.

Old-fashioned brooms or besoms have been made from ancient times using ash or hazel for the handle and a bundle of birch twigs for the brush. They are useful in the garden still, for sweeping leaves, fake versions are sold at Hallowe'en for youthful witches to wield and indeed they retain symbolic importance in modern pagan belief (Wicca). You can make a besom yourself with too much difficulty, you can buy one online from Wiccan websites or you can order one from a traditional besom maker such as this family firm that holds the Royal Warrant of Appointment as suppliers of "Besoms, Brooms and Pea Sticks" to Her Majesty Queen Elizabeth II.

If you remove one from a birch tree it probably won't be much use for sweeping and besides it might annoy the weird sisters.