Unlike anywhere else (apart from south-east Asia) Australia has land leeches. They are the bane of rainforest walkers lives. My sister's abiding memory of walking in Ravensbourne National Park is of coming home with blood soaked socks.
The leeches lurk about on the forest floor, questing about for anything mammalian that passes. Leeches are quite closely related to earthworms. They have suckers front and back, and latch on to their prey to feed on their blood. The group isn't widely studied and they are not easy to identify to species level. Whilst they will latch on to your legs at any opportunity they are not known to transmit diseases and realistically are just a minor inconvenience.