Mistletoe is a parasitic plant that lives off the nutrients and water from a host tree. Although it is parasitic, it will not kill the host tree but can weaken it.
The berries are often spread by birds from one tree to another, and this is how the large rounded clumps of mistletoe form in tree branches.
The most common host tree in the UK is apple, but poplar and lime are also frequent hosts. It is mainly found in the south and west midlands in the UK, with particularly large populations in Herefordshire.