The slugs you refer to are likely not slugs in the traditional sense i.e. the shell lacking molluscs which are relatives of snails, but rather the larvae of the cherry sawfly, Caliroa cerasi. These insects may also be referred to as cherry slugworm and were accidentally introduced to Australia from Europe. These insects can cause extensive damage to the foliage of the tree. The larvae are about 10 mm in length and are club shaped, being broader at the front than at the rear. They are greenish to orange in color and are covered in shiny slime. The larvae feed on the upper surface of the leaves and leave behind a characteristic net-like pattern of damage. The larvae pupate in the soil at the base of the tree and adult sawflies emerge 3-4 weeks later. The adults will return to the tree to lay their eggs and feed on the fruit. Their presence is indicated by a small entry hole on the unripe cherry.

The larvae are controlled in commercial orchards with insecticide sprays but can be controlled in the home garden by picking the slugs off of the trees by hand or vigorously spraying the leaves with water from a hose. Another commonly used method is to sprinkle the leaves with fine wood ash which will dry the larvae out. If you choose to pick off by hand, make sure that you squish the larvae to kill them or feed them to birds. You can prevent them climbing back up the tree by applying a thick coat of glue or vaseline around the base of the tree.