A bloodsucker on your leg can give you the willies! But let’s not be too hasty in our criticism of this lowly creature.
The leeches we have here in the northwest are not alone, by any means. There are more than 700 species of leeches in the world.
In our area, leeches live mainly in freshwater ponds and lakes. But they also live in water almost all over the world—even in the coldest of oceans, the polar seas.
And they come in all sizes, from really tiny ones to some which are as big as your forearm.
As well, they can change their body shapes from plump balls to long, slender worms, and they generally are soft and wiggly.
All leeches have two suckers, one at each end. Some species swim or crawl while some move along like inchworms, using those suckers.
They are related to earthworms and sea worms (phylum Annelidea), or segmented worms. Leeches always have 34 segments and a large central nerve, with 34 little “brains” strung along it.
They also are hermaphroditic, meaning they have both male and female organs in each leech (so do earthworms, by the way, which is why, if you are trying to catch dew worms, you often find them on the wet grass practically fastened together).
We have, here in Canada, about 50 species of leeches. Most of these eat things like little worms, insect larvae, and all sorts of pond life. Others who favour larger things often prey on snails only, turtles only, or ducks only.
They seem to be quite particular about what they feed on.
The one which likes to suck your blood is the North American Medicinal Leech (Macrobdella decora). This one feeds a lot on frogs, but it does seem to have a preference for mammalian blood.
Our leech will attach itself to any mammal which happens to come by—beaver, mink, dog, horse, or person. Why? Because mammalian blood is chock full of red blood cells, or erythocytes.
So our leech gets a lot more sustenance from mammals than it does from frogs or other cold-blooded animals.
About those two suckers. When a leech is approaching a food source (you), it attaches itself with the rear sucker—and that’s all that sucker does. Then it explores with the front one.
If it considers you a good place for a meal, it then latches on.
Our leeches have three sets of tiny teeth. These leave a circular mark on your skin, which will go away in a day or so.
There are, however, other leeches in the world which can bore through the skin of elephants or hippopotami.
If you go back to the 19th century, you will find the “golden age” of leeches. Somehow, the medical people got the idea that all diseases were caused by some defect in the blood, even gout, teething, whooping cough, and on and on.
As such, leeches were in tremendous demand all over Europe. In 1833, more than 41 million leeches were imported into France alone.
Now leeches are still used in medicine, and still are sold in some drugstores in the U.S. and Canada. Leeches are used in the re-attachment of severed fingers or ears, for example, and in plastic surgery.
Leeches also inject a bit of anticoagulant into you, and this was used in medicine for years until these chemicals were made artificially.
As well, leeches still are used to clear away the blood from black eyes, and for a few other problems.
Bloodsuckers live in some really weird places. In Canada, they often attach themselves to the nasal passages of ducks and geese.
They did bother Napoleon’s soldiers in the Mediterranean area in the 1800s, and British soldiers a century later.
Surprisingly, there still is enough interest in, and demand for, leeches that there are some leech “farms” in the world. Although most folks probably wouldn’t run to get into that business.
Here in the northwest, in a very prolific fishing area, leeches are used for bait quite a lot. Otherwise, they don’t really bother us a great deal—except maybe to scare the heck out of girls.
Anyway, they are really interesting animals, even if most people don’t like them at all. The bite is about the same as a mosquito bite.
Just imagine if we has some of them weighing in at a couple of kilograms!
Nature, Science & You logo
graphic
