Have you ever wondered about those balls of greenery growing in trees that have lost their leaves? It’s mistletoe! American or oak mistletoe grows only in deciduous trees, which shed their leaves annually. In Florida it’s most commonly found in laurel oaks but also found in elm, hackberry, sycamore and wild cherry trees.
These are parasitic and will weaken or destroy the trees it infests. More accurately they are  hemi-parasites. This means they obtain a portion of their energy through photosynthesis, and the rest is extracted from the host. Careful pruning can help but be careful, mistletoe is very poisonous to pets and children. Ecologists actually view mistletoe as an important part of a healthy ecosystem, as the berries are a major food source for birds, who also find the dense foliage useful for nesting—and the dead trees become purchase for raptors.