Blood Sucking Leeches

Post Register June 13, 2013

          To keep the kids from wandering away from their fishing poles, we once allowed them to wade in Henrys Lake. They played and splashed and had a grand time. However, they never wanted to swim at Henrys again, all because each came away with new friends—leeches.

          Just what is a leech? Leeches are segmented worms with suction cups at each end. Generally, they are flattened top to bottom and may be from a quarter inch to ten inches long.  Most live in freshwater, but there are also marine and even terrestrial species. There are almost 700 species of leeches worldwide so variation is to be expected.

          Most leeches feed on blood, but some prey on invertebrates. Many blood sucking species feed only on fish. Some will feed on any vertebrate, including humans, and a few specialize only in animals like turtles or birds.

          Most blood sucking leeches have hundreds of tiny sharp teeth on what are loosely called jaws. They use these teeth to make an incision in the host while their sucker holds them in place for a meal. A typical leech may feed from 20 minutes to two hours or more, gaining up to five times its bodyweight in blood, before dropping off.

          Leech saliva is the magic of the system. It contains a protein, hirudin, which prevents the blood from clotting. A typical leech bite may bleed for up to three days after the leech departs because hirudin is still present. This is such an effective anticoagulant that scientists have created a synthetic version useful for medical patients who cannot tolerate the blood thinner, heparin.

          Leeches are hermaphroditic, meaning that they have both male and female reproductive organs. They are not self-fertile though. They still mate, with each partner providing sperm to the other.

          Although they may be a bit repulsive, leeches are useful critters. Fishermen know that where leeches are abundant, a leech pattern in the fishing vest can make the difference between catching fish and just fishing. Leeches are also big medicine. The hirudin and blood sucking help to reduce swelling after plastic surgery and re-attachment of limbs.

          Despite what you may remember from the movie, The African Queen, where Katherine Hepburn removes huge leeches from Humphrey Bogart using Bogart’s cigar, that isn’t really a good way to remove a leech. The best way is to use a fingernail and gently push against the oral sucker until you break the seal. Then repeat with the posterior sucker and give the leech the boot.

           Leeches are likely to occur in just about any water humans might want to recreate in. To avoid having one get a free meal at your expense, do a quick check after wading or swimming.

         Henrys Lake was long ago, but since then I have pulled leeches off my own legs on several occasions. I find the experience no more disgusting than removing a tick or swatting a mosquito, but I have far less tolerance for two-legged blood sucking leeches. That kind can suck you dry.



This leech demonstrates it sucking prowess by clinging to the underside of a paddle in the Snake River below Jackson Lake Dam. This species may only feed on fish, or it might find you tasty too!