Just don’t tangle with the dreaded buffalo leech of southeast Asia, whose jaws can pierce elephant hide. Leeches are entirely carnivorous and there are few places on earth you can hide from the 700 species of the little bloodsuckers. Playful freshwater leeches idle in cool, shallow lakes, ponds and backwaters of rivers and creeks of North America, Europe and Australia, clinging under rocks, vegetation and logs. Even Antarctica has its own species.

You could find an unwelcome guest in your pants while hacking a path through the rainforests of Madagascar or Borneo, where non-aquatic cousins live in leaf litter and vegetation. Or find the blighters gnawing at you, chest-deep among the reeds, as you pull an old steamboat as if you were Bogart in The African Queen.

Everyone knows that the first thing to do when you find a leech stuck to your body is to burn it off with the tip of your cigarette. But everyone is wrong. Frazzling a feeding leech with your fag may be satisfying and pleasingly redolent of Chindits behind the Japanese lines in Burma. Unfortunately, it also has the effect of causing the leech to regurgitate its meal, thus spreading bacteria from its revolting digestive system all over your open wound.

And, of course, if you’re a non-smoker, up to your knees in a swamp, where are you going to find a lighted cigarette? No, a basic knowledge of biology is a more effective way of defeating them.

When a leech sinks its teeth into your skin, it releases both an anaesthetic and an anticoagulant, so while the bite doesn’t hurt it does tend to bleed profusely.

For an effective way to remove one, see Wildmadagascar.org (tinyurl.com/ha8q2).. Leeches hold on to their food source with a pair of suckers, so first identify the anterior (oral) sucker which, contrary to what you might expect, is at the thin end of the leech. Gently but firmly slide your first finger towards where the leech is feeding and use your fingernail to push the sucker sideways from the wound to break its seal.

Deploy another finger in the same way to detach its posterior sucker (the one at the fat end). Once you’ve flicked the leech away, take whatever revenge you feel like, perhaps by squashing, perhaps with a sprinkling of salt.

The wound itself will itch and needs to be kept clean to avoid infection.

Leeches, however, tend not to transmit disease, and the only time you really need worry about them is when you encounter the hideous variety dinobdella ferox — the ferocious leech — which specialises in climbing into nasal passages, swelling on your blood and slowly asphyxiating you.