Leeches are gruesome but pretty harmless creatures that almost all hikers will encounter. A tiny, muscular tube with teeth at one end, they lie dormant in rainforest leaf litter until, activated by your footfalls and body heat, they latch onto your boot, then climb until they find a way through socks and trousers and onto your skin. Their bites (about the size of a pinhead) are completely painless, but they bleed a lot and sometimes itch as they heal.
Keeping leeches off isn’t easy; they can get through all but the closest-mesh fabrics. Tights work (but get very hot), though some guides recommend simply wearing open shoes and shorts, so that you can see them – an approach that requires an advanced jungle mentality.
The quickest way to remove a leech is to repeatedly flick its head end with your fingernail. Otherwise salt, tiger balm or tobacco juice, rubbed onto the leech, will cause them to let go rapidly.