Following the removal of an enormous leech from the nostril of a British backpacker, we shine a spotlight on the creatures, including where you are likely to encounter them – and how to remove them if bitten.
What are leeches?
They are a type of segmented worm, with many similarities to the common earthworm in your back garden. They are hermaphrodites – meaning they have both male and female reproductive organs.
Leeches are mostly aquatic – and the majority of those are freshwater based – although some are of a land variety. In the Middle Ages, leeches were thought to have medicinal qualities – a perception that is now making something of a comeback.
Scare stories abound: in one even more vivid example to the one found sucking on a British backpacker, a leech named the Tyrannobdella rex or tyrant leech king was discovered in the remote stretches of the Upper Amazon in Peru. The 4.4cm example – with eight large teeth lining a single jaw – was extracted from the nose of a girl who had been bathing in the river.
In a new BBC documentary, Wonders of the Monsoon, a five-cm leech was filmed devouring a large blue earthworm in Borneo.
It's tales like these that frighten travellers perhaps more than they should. With the right precautions, the chances of being similarly affected are very slim, even if you visit a particularly leech-friendly region.
Where do they live?
According to the Australian Museum, they are widely spread around the world, occurring mostly in damp areas – such as streams, and rainforests – but are largely absent from arid areas.
How do I avoid them?
In some parts of the world, your chances of encountering leeches are much higher. In south-east Asia, for example, they are a particular menace in rainforest areas, where large numbers of land leeches can wait near paths and trails, and are attracted to warm-blooded passers-by.
However, you can mitigate against the risk of a painful encounter. Dr Dawood, a travel health expert, advises: "They are skilled at insinuating their mouth parts through the weave of socks, and wriggling into trainers or even tough hiking boots.
"They have a particular propensity for buttocks and private parts – so caution is needed when answering the call of nature.
"Leech bites are almost painless, and accompanied by secretion of an anticoagulant, so the first clue to their presence may be an expanding red stain in your socks or clothing, or the squelch of blood in your boots."
Dr Dawood advises purchasing leech socks, which are made from tightly woven fabric prevent the leech from attaching itself.
Otherwise he says: "you can make your own by spraying plenty of DEET (mosquito repellent) on to ordinary hiking socks."
It is harder to mitigate against aquatic leeches, apart from avoiding bathing in areas where they occur.
According to Dr Dawood, aquatic leeches can potentially attack bathers by crawling into the mouth, nostrils, eyes and genitals.
Mark Siddal, curator at the American Museum of Natural History in New York, said the British backpacker, Daniela Liverani, "could have picked up this leech from water in Vietnam, if she had been swimming.
"Or it could have gone in through her mouth as she was drinking water."
(That last suggestion is probably the least likely - another study suggests that leech attacks via drinking water generally only happen when the individual involved has a habit of taking unsafe drinking water).
How do I get rid of them if am bitten?
Dr Dawood stresses that trying to pull a leech off is not a good idea:
"If you do find a leech attached to you, don't pull it off, as the mouth parts can remain under your skin and leave a slowly healing granuloma, or lump.
"You can encourage the leech to detach on its own by heating it with a lighted cigarette; just as effectively, you can apply some DEET, alcohol or table salt. Apply antiseptic to the skin until it has healed."
The Telegraph, London