Horsehair worm, Gordius sp., an internal
parasite of crickets, cockroaches, grasshoppers, and others
The phylum Nematomorpha (from the Greek nema, "thread," and morphe,
"shape"), is a group of invertebrates called horsehair or gordian
worms. The name horsehair is derived from the worm's hair or threadlike appearance in its adult
The horsehair worms are interesting
threadlike roundworms that resemble the "hair of a horse's tail or
mane." These long, active worms may be observed during late summer
or fall in streams and ponds, but are more commonly noticed in domestic
water containers such as bird baths, swimming pools, water troughs, pet
dishes, sinks, bathtubs and toilets. They may also be found on damp
garden soil or vegetable plants after a rain (another common name is the
cabbagehair, however, this may be a parasitic nematode affecting the
same insects . . . see comments).
Horsehair worms are no bigger around
than kite string (1/25 to 1/16 inch wide) and very long (4 to 14
inches). Amazingly, the entire horsehair worm grows and develops as a
parasite inside the body cavity of crickets and other large insects such
as grasshoppers, katydids, beetles and cockroaches. This internal
parasite of insects does not harm humans, animals or plants. Horsehair
worms are white when they first emerge from the host's body. They turn
yellowish-tan to brownish-black after a short period of time. The worms
often squirm and twist in the water, knotting themselves into a loose,
ball-like shape, resembling the "Gordian Knot."
Horsehair worms reproduce sexually, in spring, early summer, or autumn.
Eggs are laid in long gelatinous strings where eggs may number in the
millions. After hatching, some experts suggest that the larvae encyst on vegetation or other
surfaces along the water's edge. Eventually, some of these cysts are ingested by hosts feeding on these
items. The cyst degenerates in the digestive tract of the new host, and
the larva burrows its way through the intestinal wall into the host's body
cavity to continue its development. If ingested by an inappropriate
host, the cyst may degenerate and then reencyst in the tissues of the host. If this inappropriate host is then ingested by
a predator which is a host, the cyst may again disintegrate and continue its life cycle in this new host. Other researchers
suggest that after the larva emerges from the egg, it penetrates the body wall of just about any animal,
though normal development occurs only in suitable hosts.
After entering the body cavity of an appropriate host, the larva grows to a juvenile stage, then emerges from the host to mature. During the larval stage of
development, the horsehair worm digests and absorbs surrounding tissue. This period of metamorphosis occurs over a period of several weeks to several months;
eventually the larval form develops into a tightly coiled mass in the host. One to several horsehair worms may occur in a single host. The parasite uses the important
nutrients of the host, probably impairing its reproductive system. One
interesting habit of infected insects is that their behavior changes as
the horsehair worm matures. Parasitized crickets are thirsty and go to
water to drink. While there the horsehair worm emerges from the insect's
body and swims away in the water, an essential step in the life cycle of
this internal parasite. Insects infected with horsehair worms die as a
result of the parasite.
Horsehair worms are completely harmless.
They do not infest people, livestock, pets or plants. They are
beneficial because of the small percentage of crickets, and other
insects that they kill. No control measures are needed when this
interesting worm is found.
There also is a very long species of
nematode, Mermis nigrescens which is a parasite of grasshoppers.
The large adult nematodes, 4 to 8 inches in length, overwinter in the
soil and under sheltering debris, emerging in late spring during periods
of overcast, humid weather. At that time they may be seen crawling about
plants as they lay eggs. Grasshoppers that ingest these eggs become
infected as the nematodes develop internally. By late summer, it is not
uncommon to find the abdomen of many grasshoppers to be packed with
these parasites. Such infections seriously stress and sterilize infected
Origin of the common names:
One common name of nematomorphs is
"Gordian worm", which originated from its similarity in
appearance to a knot, specifically one created by Gordius, King of
Phrygia around 330 B.C. As the mythical story goes, Gordius used this
knot to bind a chariot to a pole. He declared that whoever could undo
the knot would be ruler of all Asia. The challenge ended when Alexander the Great,
when not able to untie the knot, cut it apart with his sword.
The "horsehair worm" name
likely originates from what ancient observers perceived as the
spontaneous transformation of hairs from horses that, having fallen into
watering troughs, developed into living worms.