Unlike the smaller more common scribbly gum of Sydney’s sandstone country (Eucalyptus haemastoma) the Hard Leaved Scribbly Gum can grow into a 20m, straight trunked tree with a huge girth. Their age is unknown but they are likely to live for over 200 years. Substantial habitat hollows form in old trees. The trees are particularly resilient. In 1975 much of the Hills District was burnt in a wildfire. Many scribbly gums which survived these fires can be seen in the area with still signs of fire damage to their main trunks but also still very much alive.

Like other large gum trees, they host a huge population of insects and spiders: eating the leaves and each other, as well as the birds and bats that feed on them. The distinctive scribbles are made by the caterpillar of the scribbly gum moth (Ogmograptis scribula) which feeds under the bark. When the caterpillar is half grown it reverses and feeds parallel to the original course. It is fun to see the turning circle in the scribble patterns. Large quantities of nectar and pollen are available when the trees flower between January and April. The hard fruits hold masses of seeds which are eaten by rosellas.

The former Pony Club site has a large number of these trees some of them obviously very old. There is also a beautiful avenue of these trees on the track between Field No 6 and Field No 4 in Fred Caterson Reserve.

Source: The Bushland of Fred Caterson Reserve, Baulkham Hills Shire Council, 2007.