I have been an avid Nature watcher for all of my life, and it's rare when someone can bring me something for identification when I am completely stumped. However, once in awhile I find myself seeking others for advice, and once in awhile I even can walk out of my own house and be amazed by what I see sliming its way across my garden path. I'd like to share two of these oddities with you at this time, and while both of them are "worms" they are very different from our good old garden earthworm.
The first of these is called a Horsehair Worm, and it is a really frightening mystery when you see it for the first time and have no clue what it is. In reality this is a species of roundworm that is a parasite of crickets, grasshoppers, large beetles or some other large insects. It is as long as 14 inches, but is so thin that it looks like a thread, or "horse hair", and thus its name. The few times I have seen this worm it was on a sidewalk, and looked like a long, black, squirming hair. When they first emerge from the insect they have been feeding within they are white, but their color then changes to a yellowish brown and finally to a dark brown or black.
These worms are harmless to people, pets, or plants, as they restrict their role to that of eating the insides of insects. However, they are strongly attracted to water, and sometimes are found in backyard ponds, pet dishes, bird baths, writhing around and knotting themselves into a loose ball that is reminiscent of what is called the "Gordian Knot", giving them another name of Gordian Worm. What is even more disconcerting to you is that they may be found in bathtubs, sinks, or toilets, also behaving in their weird way, and what you discover is this huge, squirming worm in a place it really ought not be.
How did this worm find its way into these various water sources? Well, crickets in particular are probably the culprits that took them there, for crickets have the leaping ability to enable them to get up and into such high places. When a cricket is infected with one of these worms it becomes very thirsty, and seeks water. While at the water source the worm is stimulated to emerge from the body of the cricket, drop into the water, and swim away, and the water source is necessary for the worm to be able to continue its life cycle and future generations.
It is not only water pools that will have the worms, as other sources of high moisture content also are conducive to their survival, such as damp garden soil or even on plants in the garden after a rain or in the morning following a general watering by the sprinkler system. Since they so resemble the long, thick hairs from a horse's mane there has been a superstition that they were actually such hairs that had come to life, particularly if they had been found in a watering trough that served horses.
The insects that have been infected with a horsehair worm are killed, and this really is only a small number of insects, and thus the worms do not have a dramatic impact on a population of bugs in your yard. However, the worms can be considered beneficial for the work they do, and once again they are completely harmless to people and warm blooded animals.
The second worm we will discuss is not quite so benign, however, and this is a strange flatworm called a Land Planarian. Now, way back in college biology classes we studied neat little flatworms called Planaria, and these things could be gathered by the dozens from under rocks in a local creek. They were only about a half inch long, very flat, and had a triangular head with two big eye spots on it. The neat thing about them was how we could slice and dice them in various ways and all the pieces grew new Planaria. You could cut the head into two sections and each section would grow a new head.
So, when I walked out of my house one morning onto the damp gravel path in my garden, and noticed this flatworm about 12 inches long (!!) sliding across the gravel, I wondered what the heck it was. Since then I have found only a few more, but my curiosity was piqued. In talking with a biologist at the local university I found that these worms are parasites of our buddies the earthworm, and apparently the parasitic flatworm can be so devastating to the earthworm that it can literally wipe out populations of the earthworms in some areas. In areas of the southern United States, where earthworms are raised in rearing beds, the flatworm is a severe problem.
This worm looks very much like the cute little planarian I studied in school, except it is so much longer. It is flat, has dark stripes running the length of its body, and has a similar shovel-shaped head. As it moves it can stretch out up to 20 inches long, gliding along on a thin layer of mucus secreted from glands along its underside. When they have found an earthworm to eat they use this slime to entangle the worm and hold it still. At that point the Science Fiction Theater enters, as the flatworm actually feeds by extending its throat out of its mouth and into the earthworm, and small bits of the worm are swallowed a little at a time. The mouth, by the way, is located on the worm's belly, somewhere around the middle of the body. The mouth also serves as the anus for this strange creature.
To continue with this "I can't believe it" scenario, while the flatworm parasite does lay eggs to produce offspring, it seems that a principal means for reproducing is simply by breaking off little bits of itself. Every couple of weeks a short segment at the tail end of the worm will stick to the surface as the worm slimes over it, and that segment breaks off. Immediately this lost section can move about on its own, and within about one week a new head has begun to form.
These creatures are a potential problem in the United States. They do not belong here. It is believed that they are native to Indo-China, but are transported to many other parts of the world in soil, particularly in the potted soil of greenhouse plants. They have been found commonly in the United States in greenhouses since around 1900, and they thrive in this humid, tropical environment. They have been reported in greenhouses from New York to Florida and across the continent to California, as well as in outdoor environments in many states. The species name for the creature I have found is Bipalium kewense, and it is believed that its natural range is from Vietnam down into Malaysia. The species that is so big a problem in England and Ireland is called Artioposthia triangulata, and it is reported to be capable of eliminating entire populations of earthworms on farm properties.
This and related species of parasitic flatworms are also in Australia, New Zealand, and Great Britain, and in these countries they are terrible pests of the earthworms. While they can survive in climates where winter temperatures drop below freezing, they don't do well in dry climates. As a tropical animal they so far have not been found in desert areas of the United States. They are primarily nocturnal, but sometimes you will find them still out and about early in the morning on wet surfaces.
While the first kind of worm we discussed, the cricket parasite, is a native animal and is not an environmental problem, the second one - the hideous flatworms - potentially are major problems for native populations of earthworms. This points out the extreme importance of keeping exotic plants and animals out of countries of the world where they do not belong. When they are displaced they can have a severe impact on the native organisms in their new environment.