An e-mail from a friend described a recent encounter she and her son had with leeches in the Willamette River.

Leeches? In the Willamette? While many people may equate leeches with murky, tropical rivers, leeches live all over the world, in a wide variety of habitats. Of the 650 species world-wide, about 45 species live in the US and perhaps a half-dozen live in fresh Oregon waters like the Willamette River...or Coos County.

Though most leech species live in fresh water, about 20 percent live in salt water and a few live on land in wet, tropical habitats. Wherever they live, they’re popular food for other animals.

Most leeches are familiar to people, either by experience or reputation, for feeding on the blood of vertebrates, ranging from fish to humans. Some bloodsucking leeches have rings of sharp teeth around their mouths that slice a painless wound, others have a long, hollow proboscis that is used to puncture and suck.

Leech saliva is said to have anesthetic properties that numb the bite area. Leeches produce an anticoagulant, called hirudin, that keeps the meal flowing and ensures dinner doesn’t form an indigestible lump in the leech’s gullet. It takes about a half-hour to satiate a bloodsucking leech — which can mean ingesting up to eight times its weight in blood. Once full, a leech drops off the host and can then live off its blood meal for several months.

A leech’s gut has special organs that house symbiotic bacteria that provide necessary nutrients that aren’t in the leech’s blood meals. Leech bacteria can get loose in the victim’s bloodstream and perhaps cause infection if the leech is removed improperly. Proper detachment of a leech involves sliding a fingernail or something similar under the suckers to release the suction.

Most leeches suck blood, but not all. Some are predators that slurp small invertebrates whole through a toothless mouth.

All leeches are annelids, or segmented worms like earthworms; each of the leech’s 34 segments has its own small brain. The first few segments and last few segments form the suckers at each end of the leech. The narrow-end sucker is the mouth.

Leeches can swim by undulating through the water, but apparently most movement is by alternatively attaching and releasing the two suckers, rather like an inchworm. Slippery and squirmy, leeches can squeeze just about anywhere. And while they are water-loving animals, many can survive being dried out a while.

Most leeches are well camouflaged in brownish, blackish or greenish hues, and some are patterned. They seek out dark crevices and nooks with the help of two to ten primitive eyes.

The sex lives of leeches are interesting, too. Like their earthworm cousins, leeches are hermaphrodites — male and female at the same time. While most leeches lay their eggs in cocoons directly into their habitat, the proboscis-wielding group broods eggs and young, with some even feeding their babies.

My friend’s son found leeches under rocks, and later, on his leg.

People have purposefully placed leeches on legs and elsewhere for more than 2,000 years, primarily for “bloodletting.”  Today, leeches are used medically to drain blood collecting under skin grafts and draw blood to places it’s needed while damaged tissue heals.

Though most leeches are only an inch or two long, medicinal leeches (Hirudo ssp.) grow up to eight inches long. The Amazon giant leech can grow to 18 inches — as long as an adult’s forearm.

My friend’s son was  put off by the small leeches that had been attracted to him. Imagine finding a leech the length of your forearm. (Don’t worry — not here.)

For information on how to arrange an exploration of our fascinating natural history for your group or your visiting guests, contact Marty at (541) 267-4027, or e-mail mgiles@wavecrestdiscoveries.com. Questions and comments about local natural history are welcome.