Leeches are usually only noticed when attached to you!
The mere mention of the word "leech" sends shivers up the spines of some people, which is quite unfortunate given the fascinating lives these small creatures live. Many people who bushwalk in Tasmania will have stories to tell of personal encounters with leeches.
Leeches are anneilds, and are closely related to earthworms. There are 650 known species of leeches. About one fifth of leech species live in the sea, where they feed on fish. The largest leech discovered measures nearly half a metre in length and, fortunately, does not live in Australia!
Terrestrial leeches require damp environments as their skin must be kept moist to allow oxygen to diffuse across it.
About 100 species are known from Australia, and at least a dozen are found in Tasmania - most of which live in water. Many of these aquatic species lack the mouthparts that enable their familiar terrestrial cousin to attach to human skin, while others are parasitic on fish and freshwater snails. It is likely that there are still many undescribed Australian species.
Among the common species in Tasmania are Philaemon pungens, reaching about 20mm, and the striped P. grandis, or Tiger leech, which reaches about 56mm.
Leeches are hermaphrodites, each individual having both male and females reproductive organs. In some species, eggs are layed in cocoons that ar left in damp places. The cocoon contains stored energy that sustains the developing eggs and hatchlings with no further investment from the parents. There is no larval stage - young leeches look like small adults.
Some species of leeches are devoted parents. Parental brooding of egg clusters may take place in a external nest, on the parent's body or occur in a marsupial-like pouch. In addition, some genera are known to transfer nutrients across the body wall to the developing young in a manner reminiscent of a 'placenta'.
The bite of a leech is painless, due to its own anaesthetic. An anti-coagulant serum is injected into the victim to prevent the blood clotting.
The leech will gorge itself up to five times its body weigh until it has had its fill and then just fall off. A leech can survive several months to a year before feeding again.
Leeches are best removed by breaking the seal between the skin and the mouth with a long fingernail. Other common remedies include applying salt to the leeches body, or a flame. Due to the anti-coagulant, a leech bite can bleed for several hours.