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A Worm That is Our Enemy!!
common name: land planarians
scientific name: Bipalium kewense Moseley and Dolichoplana striata Moseley (Tricladida: Terricola)
Esser
(1981) discussed land planarians in Florida. He stated that in almost
every month of the year specimens of grey to brown long flat worms with
several dark stripes running down the back were submitted to the
Nematology Bureau for identification and information concerning their
biology. These worms were land planarians included in the phylum
Platyhelminthes. Almost all specimens submitted belonged to the genus Bipalium.
The land planarian Bipalium kewense
Moseley was first described from a greenhouse at Kew Botanical Gardens
near London, England, in 1878. This species is believed to be native to
Indo-China, and has been found commonly in American greenhouses since
1901.
Reproduction and Development:
Reproduction is principally by fragmentation at the posterior end.
Lateral margins pinch in about 1 cm from the tail tip. Severance occurs
when the posterior fragment adheres to the substrate and the parent
worm pulls away. The posterior fragment is motile immediately, and
within seven to 10 days a lightly pigmented head begins to form. One to
two fragments are released each month.
Eggs are deposited in 0.6
to 9.7 cm cocoons that are bright red when deposited. Within 24 hours
the cocoons turn black. Planarians emerge in approximately 21 days.
Habitat:
Because land planarians are photo-negative during daylight hours and
require high humidity, they are found in dark, cool, moist areas under
objects such as rocks, logs, in debris, or under shrubs, and on the
soil surface following heavy rains. Land planarians are also found in
caves, but are rare in rural sites. Movement and feeding occur at
night. High humidity is essential to survival. They can survive
desiccation only if water loss does not exceed 45 percent of their body
weight. Land planarians are most abundant in spring and fall.
Dundee and Dundee (1963) reported B. kewense as being plentiful enough in New Orleans to be used as demonstration material in zoology classes.
Locomotion:
Land planarians glide smoothly on the substrate by the action of
powerful, closely spaced cilia in a special medial ventral strip
(creeping sole), on a thin coat of mucus secreted on the substrate by
glands opening into the creeping sole. Land planarians that migrate on
plants or objects above the ground sometimes regain the ground by
lowering themselves down by a string of mucus.
Nutrition: Land planarians devour earthworms,
slugs, insect larvae, and are cannibalistic. Prey are located by
chemoreceptors located in a single ciliated pit under the head or in a
ciliated ventral groove. Struggling prey are held to the substrate and
entangled in slimy secretions from the planarian. The pharynx is
protruded from the mouth and into the prey. Food is reduced to small
particles prior to entering the gastro vascular cavity. The food
particles are taken by epithelial cells in amoeboid fashion and formed
into food vacuoles. Planaria store food in digestive epithelium and can
survive many weeks shrinking slowly in size without feeding. They are
capable of utilizing their own tissues such as reproductive tissue for
food when reserves are exhausted.
Planarian attacking earthworm. A. Planarian B. Earthworm. (From Esser 1981).
Planarian Enemies:
Other animals rarely devour land planarians, since surface secretions
appear distasteful, if not toxic. Protozoans, including flagellates,
ciliates, sporozoans, and nematodes have been detected in land
planarians. Because of their cannibalistic habit, land planarians may
be their own worst enemy.
Planarians are voracious predators on earthworms, and two species, B. kewense and Dolichoplana striata
Moseley, have been reported as nuisances in the southern USA in
earthworm rearing beds. (Hyman 1954; Dunn, personal observation 1997)
Two additional flatworm species, Artioposthia triangulata and Geoplana sanguinea,
were accidentally imported to Ireland and England. They were reported
as being capable of eradicating entire earthworm populations on farms.
In greenhouses, although some collectors believe they might damage
plants, they are considered harmless.
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