Horsehair worms and two human parasites

Compiled by Bob Bowles
Aborted Entolma regular form, Honey Mushroom and Hunter's Hearts, the aborted form of the Aborted Entolma ( BOB BOWLES Submitted photo)

Aborted Entolma regular form, Honey Mushroom and Hunter's Hearts, the aborted form of the Aborted Entolma ( BOB BOWLES Submitted photo)


I remember observing horsehair worms as a boy in the water trough on the farm in Grey County on a few occasions and wondering if they came from the horses and cattle drinking water from the trough.

This year, I was contacted by someone who found one in his swimming pool and was concerned and wondered what it was and if it would harm the pool users or if it was a human parasite.

Legend has it that horsehairs would mysteriously come to life in the town watering trough. These are unsegmented, hard, opaque worms called Gordian or horsehair worms in the phylum Nematomorpha. They can grow to 100 centimetres (40 inches) in length, but are usually just over 30 centimetres (one foot) and range from 1 to 1.6 millimetres (1/25 to 1/16 of an inch) and uniform in length from head to tail. Horsehair worms vary greatly in colour from whitish to yellowish tan to brown/black. They are found on the ground or on plants, especially near water, and move by undulating, sometimes becoming entangled with one another in large masses where they live in small pools of water. Gordian worms mate in spring, early summer or fall and often intertwine, forming a loose ball during mating - this gives rise to their common name. A classical myth tells of Gordias, a poor peasant who, when made king of Phrygia, tied his ox cart to a post with a very difficult knot. It was prophesied by an oracle that he who could untie this Gordian knot would become king of Asia.

After mating, horsehair worms lay eggs in a long, gelatinous string in fresh water. A small worm emerges from each egg and lives on aquatic vegetation where it is engulfed by crustaceans, molluscs, arthropods, insects or other invertebrates, which they infect as a host. They attack a wide variety of insects and related animals like grasshoppers, crickets, cockroaches, beetles, katydids, dragonflies, caddisflies, millipedes, centipedes, spiders, crustaceans, leaches, snails, slugs and other invertebrates. The worms then live as parasites in their hosts until mature, then emerge when near water to live in either standing or running fresh water in puddles, water tanks, ditches, swimming pools, small ponds or on plants near water. They have even been observed inside homes in toilets, which causes great concern as people often think that they have found some type of human parasite. Adults are free-living and do not feed.

Horsehair worms are especially common after a rainfall and often seen in these locations in the spring or early summer and again in the fall. They are harmless to people in all stages of their lives. They are not considered a human parasite, but there are some records that are believed to be the result of accidental ingestion of the worms in either food or water. Horsehair worms are harmless to people, pets and plants, so no control is necessary. They are nothing more than a curiosity and in fact are actually beneficial since they can effectively control certain insects.


Two common and contagious human parasites that can be contracted by drinking water from rivers and streams without boiling it first are giardiasis and amebiasis.

Giardiasis, sometimes called "beaver fever," is caused by the one-celled microscopic parasite Giardia lamblia, which lives in the intestines of people and animals. It causes diarrhea, stomach cramps, nausea, weight loss and tiredness. These symptoms can last from one to three weeks. The parasite is passed in the bowel movement of an infected person and can be contracted by others. It is recognized as one of the most common causes of waterborne diseases in humans in North America.

Amebiasis is a disease caused by another human microscopic parasite, Entamoeba histolytica, which attaches itself to the large intestine. In most cases, it causes no symptoms, but can invade deeply into the intestine or even spread in rare cases to attack the liver and other organs. Boiling water that has been contaminated with these two parasites will kill them.


There are segmented intestinal worms that are parasites of the intestinal tracts of mammals, including humans, that include roundworm nematodes (hookworms, pinworms, whipworms and threadworms) and the large tapeworms (Cestodes). Tapeworms can live up to 25 years within the host and have been known to grow to 10 metres in length within the gastrointestinal tract.

Intestinal worms are more common in human populations than some people realize. Proper disposal of body wastes, attention to good sanitation, wearing shoes where the soil is infested, as some worms can penetrate the intact skin in bare feet, will best prevent this infestation from occurring. I always wear shoes and never go in bare feet during the ecotours I lead in Central and South America, since I know of cases where humans have contracted parasite worms by going in their bare feet. Washing produce thoroughly, washing your hands well before preparing or eating foot, after changing a diaper or using the toilet will decrease your chances of contracting parasitic intestinal worms. Also, make sure your pets are treated for intestinal worms, since humans can contract worms through their pets.


There are still almost three weeks of autumn before the first day of winter, but I have a feeling the weather is going to look more winter-like from now on. Before we close the book on autumn, there is one more highlight I would like to mention from the fall before the ice and snow.

The aborted entoloma, Entoloma abortivum, is a good edible mushroom that is fairly common in our area. It is a grey-brown gilled mushroom with a white stalk - a description that would fit more than 100 other species in the area - but it has pinkish gills and spore print. The interesting feature about this species is that it is attacked by the spores of the edible honey mushroom, which makes it abort into roundish to irregular masses. Mushroom hunters called this aborted form hunter's hearts, which are even better edibles than the regular form. The highlight this fall was that both forms of the aborted entoloma were exceedingly abundant, allowing collectors to fill their collecting pots in just a few minutes. In all my time studying mushrooms in the area, I have never seen the aborted entoloma as abundant as it was this fall.

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