Terrestrial leeches are generally small (although they can get quite huge in some parts of the world) but will gorge themselves during a meal, gaining up to ten times their weight. The single feeding will be enough to sustain a leech for several months.
The best protection against leeches is covering up and using insect repellent on clothing, although they are extremely persistent and invariably if you spend enough tromping around in the forest you will get leeched. Do not get overly concerned about a leech attack — they carry no disease and there is low risk of causing significant blood loss. Leech bites do not hurt — since they release an anaesthic when they sink their teeth into your skin — but they do bleed profusely. Leeches use an anticoagulant when they bite to faciliate the flow of blood from the wound.
Removing a leech
If you are bitten by a leech and are compelled to remove it before it has had its full (leeches drop off on their own when they are done feeding), you can do so by following these steps:
1. Identify the anterior (oral) sucker which will be found at the small end of the leech.
2. Put your finger on your skin adjacent to the oral sucker
3. Gently but firmly slide your finger toward the wound where the leech is feeding. Using your fingernail, push the sucker sideways away from your skin.
4. Once you have dislodged the oral sucker, quickly detach the posterior (rear) sucker (the fat end of the leech). Try flicking the leech or proding with your fingernail. As you work to remove the leech, it will attempt to reattach itself.
5. Keep the wound clean - minor cuts in tropical climates can quickly become infected. The leech itself is not poisonous. The wound will itch as it heals.
NOTE: Is it generally not advised to attempt removing a leech by burning with a cigarette; applying mosquito repellent, shampoo, or salt; or pulling at the leech. This can result the leech regurgitating into the wound and causing infection much worse than the leech bite itself.
In the case that a leech invades an orifice like your nose, ear, or mouth you have a slightly more serious problem since the leach will expand as it fills with blood. If you have access to strong (drinkable) alcohol or hydrogen peroxide you can try gargling (if the leech is in your mouth). Worst case scenario you may have to puncture the leech with a sharp object.
source: www.wildmadagascar.org/overview/leeches.html
