Leeches - wonderful micropredators!
Image: Blood continuing to ooze from two leech bites 30 mins after leeches had gone. Yungaburra, Queensland.
Leeches are not monsters of the rainforest. They are amazing sangivorous micropredators! THS Director, Rick Speare, discusses leeches in his recent column in Medical Observer.
Leeches secrete a cocktail of chemicals in their saliva to facilitate blood flow and interfere with blood clotting. The two most interesting compounds are hirudin, which is a potent antithrombin, and calin, which prevents platelet adhesion to collagen and inhibits platelet aggregation. After the leech has dined for 10 minutes or so and departed, the wound continues to ooze blood. Bleeding can be very persistent. Ten hours is reported as the average time that oozing persists. However, there have been reports of bleeding lasting a week.
Some people develop an itchy, erythematous papule at the bite site over several days. It persists for weeks. Do not scratch!
Repellents work! If you don't want to be prey to a leech, use DEET, DMP or even oil of callistemon. Soap is also reported to keep leeches off, but there are no comparative trials.
Speare R. Blood suckers of the crawly kind. Medical Observer November 2013.
Posted by Rick Speare