Many Tamborine Mountain residents and visitors become involuntarily closely familiar with our local leeches, particularly after wet weather. Leech bites are not dangerous although they may become irritated after a few days. Most people are far more traumatised by an attack of squeamishness than by any physical symptoms.

Worldwide there are over 500 species of leeches, they are segmented worms (annelids) and are widely distributed in freshwater, marine and terrestrial environments. Respiration occurs through the body wall so they require damp conditions. They have tough muscular bodies capable of expanding to hold a blood meal that may be five times its usual weight. Jawless species of bloodsucking (sanguivorous) leeches extract blood through a straw like proboscis and jawed leeches use jaws armed with many tiny teeth to extract blood (2 jawed leeches leave a V shaped mark and 3 jawed leeches leave a Y shaped mark).

Leeches have two suctions, the anterior around the mouth to connect the leech with its host for feeding and a posterior suction near its tail used for locomotion and stability. The typical “inch worm” or looping movement is made by the leech stretching forward attaching to the ground with its front suction then bringing its tail suction close behind, attaching the tail suction detaching the front suction and then stretching forward again.

When a hungry leech is searching for a meal it usually climbs onto low foliage, attaches itself with its tail suction and extends its body. The leech has chemical receptors and sensory organs, which can detect changes in light intensity, temperature and vibrations. It waves its body to help it to detect an approaching host. When the host comes within reach the leech attaches itself, then inch worms over the host until it finds a suitable site. Once this is located the leech latches on strongly with its mouth suction, secretes mucus to seal the suction, then injects the host with a cocktail of vasodilators, anaesthetics, antinflammatories and an anticoagulant called hirudin. The leech uses its many tiny teeth to make many tiny incisions through the host’s skin, the anti coagulant ensures that the host’s blood flows freely and this is swallowed by the leech. When it is satiated usually after about an hour the leech detaches its suction and drops off the host. The leech then retires to a dark damp place to start the slow process of digestion.

Leeches have been used medically for thousands of years. The advent of microsurgery has revived their use in modern medicine. The breeding of medical leeches is now a multi million-dollar industry. Medical leeches must be kept hungry, they are used on one patient only, after each session they are placed in salt water to regurgitate their blood meal and after the patient no longer requires their services they are placed in a container of lethal methylated spirits.