woods. Mosses, ferns and liverworts frequently occur as epiphytes, attached to the trunks and branches of oak trees. Rare species growing in the woods include Cyclodictyon laetevirens, Daltonia splachnoides, Lejeunea flava, Radula carringtonii, and Sematophyllum demissum. Bird species that reside in the oak woods include blue tit, common chaffinch, goldcrest, European robin, and wren. Mammals include badger, fox, pine marten, red deer, sika deer, and red squirrel. Insects include many species of the parasitic gall wasp and the purple hairstreak butterfly, whose caterpillar is entirely dependent upon oak trees. The introduced common rhododendron is a large threat to certain areas of the oak woods. For example, it is widespread throughout Camillan Wood despite ongoing attempts to control it. Yew woodlands The yew woodland in the park is known as Reenadinna Wood. It is about in size and is located on low-lying karst limestone pavement between Muckross Lake and Lough Leane on Muckross Peninsula. Yew woodland is the rarest habitat type in the park. Yew woodlands are one of the rarest types of woodland in Europe, mostly restricted to western Ireland and southern England. It has priority habitat status under Annex I of the EU Habitats Directive. Reenadinna Wood is also one of the largest woods that are dominated by common yew (Taxus baccata L.) in the UK and Ireland. It is the only significant area of yew woodland in Ireland and is one of just three pure yew woodlands in Europe. It is of considerable ecological and conservation interest, as yew is rarely a woodland dominant. The western limit of the wood lies along the geological boundary with Devonian Old Red Sandstone. The wood is bounded to the east by parkland where the limestone no longer outcrops. Muckross bog, a raised bog in area, is in the southern part of the wood. There are hollows between the limestone outcrops. Deep rendzina soils have developed in some of the hollows. It is estimated that the wood developed 3,000–5,000 years ago. Yew is a native evergreen tree that grows best in the high humidity of mild oceanic climates, which makes Killarney a very suitable location. The soil in the wood is mostly thin and in many places the trees are rooted to fissures in the bare limestone. Yew has an extensive horizontal root system. In the Killarney woods, the roots spread out over the rock surface and penetrate deeply into fissures in