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2007 SOUTHEASTERN NATURALIST 6(3):449–460
Natural History Observations on Bipalium cf. vagum Jones
and Sterrer (Platyhelminthes: Tricladida), a Terrestrial
Broadhead Planarian New to North America
Peter K. Ducey1,*, Matthew McCormick1, and Elizabeth Davidson1
Abstract - An increasing number of exotic terrestrial planarian species have
established populations worldwide. In North America, the most prominent invasive
flatworms are three members of the broadhead planarian genus Bipalium.
Herein we report observations on the morphology, predatory behavior, and reproduction
of Bipalium cf. vagum, new to this continent and report its occurrence in
Florida and Texas. Individuals of this species have a distinctive combination of
head shape and pattern of dark dorsal pigmentation (large head spots, complete
collar, and prominent median stripe) that distinguishes them from other members
of the genus. Although the other North American species of Bipalium feed on
earthworms, B. cf. vagum feeds exclusively on terrestrial mollusks. Their predatory
behavior includes following mucus trails and subduing the prey by capping
the prey’s head with the flatworm’s anterior end and wrapping the prey’s foot in
the body of the planarian. Members of this species reproduce via egg capsules
that contain small numbers of offspring. Because this is the first land planarian
reported in North America that is a predator of mollusks, native land snails and
slugs are unlikely to have effective defenses against it. Therefore, we should
continue to monitor its geographic spread and potential ecological impact.
Invasive species are increasingly being recognized as major threats to
ecosystems worldwide (Cox 2004, Sakai et al. 2001). Although much research
is now being directed to the ecological and evolutionary processes
involved in invasion, relatively little attention has been focused on soil fauna
despite their potential impact on native and agricultural ecosystems (Lee
1985, Wardle et al. 2004). Many species of terrestrial planarians have been
described as invasive, exotic species in soils of the Northern Hemisphere;
predominant among these are Arthurdendyus triangulatus (Dendy), invading
the British Isles and Faroe Isles from a native range in New Zealand
(e.g., Blackshaw and Stewart 1992, Christensen and Mather 1995); Bipalium
kewense Moseley, now found in tropical and warm temperate regions worldwide
from hypothesized origins in southeastern Asia (Winsor 1983); and B.
adventitium Hyman, currently known only from North America but presumably
from a homeland in Asia (Ducey and Noce 1998; Hyman 1943, 1954;
Ogren and Kawakatsu 1998).
In North America, although about a dozen species of exotic terrestrial
planarians have been found (Ogren and Kawakatsu 1998), two species are
1Department of Biological Sciences, State University of New York at Cortland,
Cortland, NY 13045. *Corresponding author - email@example.com.
450 Southeastern Naturalist Vol. 6, No. 3
most conspicuous: B. adventitium, occurring across the northern portion of
the United States (Ducey and Noce 1998, Hyman 1954, Ogren 1984,
Zaborski 2002), and B. kewense, found across the southern portion (Ducey
et al. 2006, Ogren 1984, Ogren and Kawakatsu 1998). Both of these
species are predators of earthworms and are most common in disturbed
habitats associated with humans (Ducey and Noce 1998, Ogren 1984).
They differ internally in morphology of their reproductive structures and
externally in general body size, shape, and coloration (Ball and Sluys 1990,
Ogren 1984, Ogren and Kawakatsu 1998). The two species, although both
potentially hermaphroditic, also differ in reproductive ecology; B.
adventitium reproduces sexually to produce egg capsules (Ducey et al.
2005, Ogren 1984), whereas B. kewense reproduces primarily via fragmentation,
with only rare sexual production of egg cases (Connella and Stern
1969, Ducey et al. 2006, Winsor 1983). A third Bipalium species in North
America, B. pennsylvanicum, known from only two sites in Pennsylvania,
shares some morphological, reproductive, and behavioral features with B.
adventitium, but differs in appearance (Ogren and Sheldon 1991). Because
of their rapid dispersal, broad distribution, and effective predation on
earthworms, the potential impact of these species on agricultural, horticultural,
and natural ecosystems is of concern. To our knowledge, no other
species of Bipalium have been reported living outdoors in North America,
despite some 100+ members of the genus living in other parts of the world
(Ogren and Kawakatsu 1998, Winsor 1983).
Herein, we report on the occurrence of a member of the genus Bipalium
new to North America, and describe aspects of its morphology, behavior,
and reproduction. The external morphology of this species most closely
resembles that of Diversibipalium sp. 10 of Wu et al. (2005) from Taiwan
and B. vagum Jones and Sterrer, recently proposed for specimens from
Bermuda (Jones and Sterrer 2005). Because the latter two taxa have not been
formally synonymized and molecular comparisons between these flatworms
and the North American species have not been completed, we will use the
designation Bipalium cf. vagum to refer to the North American taxon
throughout this document. We distinguish this species from the other members
of the genus currently known from this continent, as well as from
congeneric species reported from other parts of the world.
Three individuals of B. cf. vagum were collected by Dan Hodgson in
Cypress, Harris County, TX in May, 2005 in a suburban yard along with
many B. kewense and a few Geoplana arkalabamensis Ogden and
Darlington. They were transported alive to the State University of New York
at Cortland, where we held them separately in plastic containers filled with
moist paper towels at 19–23 °C while they were tested for predatory behaviors.
In November, 2005, Matt Cormons sent photographs of what appears to
2007 P.K. Ducey, M. McCormick, and E. Davidson 451
be this species from Lehigh Acres, Lee County, FL, and in January, 2006,
sent a live specimen collected by Grace Donaldson Cormons. The adult
flatworms were maintained on a diet of Arion spp. and Deroceras sp. (slugs)
and Discus spp., Helicodiscus spp., and Succinea spp. (snails) (all found
locally). We fed mashed snails to the newly hatched offspring. The specimens,
tissue samples, and photographs are held in Bowers Science Museum
of SUNY at Cortland (Accession: P.K. Ducey; catalog numbers: 549, 549A,
550, 550A1, 550A1A, 550A2, 550A3, 550B1, 550B1A, 551, 551post, 574).
We compared B. cf. vagum with hundreds of newly collected and laboratory
raised B. adventitium and B. kewense. The B. adventitium were from
California, Maryland, Michigan, New Hampshire, New York, Ohio, and
West Virginia, and the B. kewense were from Arkansas, California, Georgia,
Mississippi, North Carolina, and Texas. We maintained members of
these species individually under the same physical conditions as B. cf.
vagum, but fed them earthworms. All morphological comparisons were
based on living specimens.
To examine the predatory choices and behavior of B. cf. vagum, we
subjected each adult individual (n = 3, Texas) to a series of trials with
different potential prey items. We ran the trials in plastic containers (25 cm
x 14 cm) lined with moist paper towels and partly covered to reduce light.
Test subjects were left undisturbed in the chambers for at least 5 min. for
acclimation before testing. We presented prey items individually < 1.5 cm
in front of the head of the flatworm. All potential prey items (including:
Aporrectodea turgida, Amynthas sp., Eisenia fetida, Lumbricus rubellus,
and L. terrestris [earthworms]; Arion spp. and Deroceras sp. [slugs]; Discus
sp., Helicodiscus sp., and Succinea sp. [snails]; Armadillidium sp. and
Porcellio sp. [isopods]; Oxidus sp. and Ptyoiulus sp. [millipedes]; and
Exomala sp., Limonius sp., Phyllophaga sp., and Popilla sp. [beetle larvae])
were collected in Cortland County, NY, and each prey species was
offered in at least six separate trials.
We compared the results of these trials with other observations we have
collected over the last ten years on the prey choice and predatory behaviors
of B. adventitium and B. kewense (Ducey et al. 1999; Ducey and Noce 1998;
Fiore et al. 2004; P.K. Ducey, unpubl. observ.) and with observations reported
by others (Dindal 1970, Ogren and Sheldon 1991, Zaborski 2002).
Results and Discussion
External morphology of B. cf. vagum
Like all members of the genus, members of B. cf. vagum have a broad,
spatulate head that is wider than the body (Fig. 1). In life, the auricles may
show very slight recurvature. A creeping sole runs medially the length of the
ventral surface. Live adults were 3.7—4.9 cm long (mean = 4.0 cm, n = 4)
and 0.3—0.4 cm wide (mean = 0.33 cm). All individuals possessed a thick
452 Southeastern Naturalist Vol. 6, No. 3
black transverse band on the neck (= collar) that is complete dorsally and
extends well onto the ventral side, but does not include the creeping sole
(Fig. 2b). In 3 of 7 individuals, a thin median stripe extended from the collar
onto the head. All individuals had a dorsal base color of yellow-tan with
three longitudinal dark stripes extending from the dark collar posteriorly the
full length of the body. The median stripe is the darkest stripe (same color as
the collar) and is about as broad as the diffusely pigmented lateral stripes.
The head had two dark patches, separated from each other and the neck
Figure 1. Bipalium cf. vagum from Cypress, TX—a new species for North America.
2007 P.K. Ducey, M. McCormick, and E. Davidson 453
collar by narrow lighter areas, giving the head the appearance of having two
Morphological comparison to other North American species of Bipalium
General body size, shape, and base color of B. cf. vagum are similar to
those of B. adventitium, although B. adventitium is slightly narrower in both
the head and body. Throughout its range, B. adventitium has a single, narrow
dorsal stripe, lacks the dark collar, and has only diffuse dark pigment
concentrated distally on the head, making it easily distinguishable from B.
cf. vagum. (Fig. 2).
Although considerable intraspecific diversity of appearance has been
attributed to B. kewense, at least some of this is due to historical
misidentifications (Winsor 1983). Our collections of B. kewense from the
United States agree with the descriptions, photographs, and illustrations for
this species in the literature (e.g., Connella and Stern 1969, Ogren 1984,
Winsor 1983). Similarities between B. kewense and B. cf. vagum include a
median dark stripe, a pair of more diffuse lateral stripes, and a dark collar.
However, in contrast to the appearance of B. cf. vagum, B. kewense has a
median stripe that is very narrow, a collar that is incomplete dorsally and
barely reaches the edge of the ventral surface, auricles that have distinct
recurvature, an additional dark stripe along each lateral margin (= 5 total
dorsal stripes), and a head with diffuse gray pigment concentrated medially
(Fig. 2). Adults of B. kewense attain much greater length (regularly > 15 cm)
than adults of B. cf. vagum; B. kewense of equivalent length with B. cf.
vagum are considerably thinner.
The original account of B. manubriatrium (now a synonym of B.
kewense) in North America by Sharp (1892) described the median stripe as
the broadest of the stripes, and Fletcher (1887) also stated that the median
stripe could be as broad as the lateral stripes in some specimens of B.
Figure 2. Diagrams of the typical head pigmentation for the three species of Bipalium
widely distributed in North America. A) B. adventitium, B) B. cf. vagum, C) B.
kewense. Photographs of the geographically restricted B. pennsylvanicum are available
in Ogren (1987).
454 Southeastern Naturalist Vol. 6, No. 3
kewense. Winsor (1983) likewise reported that the degree of dark pigment on
the head varies among individuals in B. kewense. However, none of the
specimens of B. kewense from North America, from our studies and previous
works (e.g., Chandler 1974, Connella and Stern 1969, Ogren 1984), nor
specimens from around the world (Winsor 1983), closely match the appearance
of B. cf. vagum.
Ogren (1987) described B. pennsylvanicum as possessing three dorsal
stripes, with the median stripe being prominent. His descriptions and illustrations
suggest that B. pennsylvanicum differs from B. cf. vagum in lacking
a dark collar, lacking dark head pigmentation, and having the median dorsal
stripe that extends onto the head. Thus, B. cf. vagum can clearly be distinguished
by external appearance from the three congeneric species previously
known to occur on this continent.
Interestingly, two public websites depicting pest animals in Florida
have included photographs of what appear to be B. cf. vagum
(Florida Nature 2006, University of Florida Institute for Food and Agricultural
Services 2006). The flatworms depicted in the photographs appear
identical to our live specimens from Florida and Texas and were originally
labeled as B. kewense on the websites. One of those specimens was collected
in Tallahassee (Florida Nature 2006), and the other in Gainesville
(P.M. Choate, University of Florida, Gainesville, FL, pers. comm.). These
sites are over 1000 km from the Cypress, TX locality and hundreds of
kilometers from the Lee County, Fl site, indicating that B. cf. vagum may
already be distributed across the Gulf Coast of the United States.
Comparison to species of Bipalium outside North America
Because the description of B. cf.vagum from Bermuda provided by
Jones and Sterrer (2005) closely matches the appearance of the planarians
we studied from Texas and Florida, and matches Diversibipalium sp. 10
from Taiwan (Wu et al. 2005), it is likely that all three studies involve the
same species. However, such synonymy should await the outcome of molecular
studies. To find possible previous descriptions of this species from
elsewhere in the world, we also examined the literature that referred to
three-lined species of Bipalium, including works by Graff (1899),
Whitehouse (1919), Kaburaki (1922), Beauchamp (1939), Winsor (1983),
Ogren (1987), and Sasaki (2001). We found, as did Jones and Sterrer
(2005), that no previously described species of Bipalium had the combination
of a dark complete collar, broad median stripe not reaching the head,
and large head spots that we found in B. cf. vagum.
Contrast in prey choice
The individuals of B. cf. vagum that we tested preyed only on gastropods
(Table 1), in contrast to the other North American Bipalium that feed
exclusively on, or with strong preference for, earthworms (Dindal 1970,
Ducey et al. 1999, Neck 1987, Ogren and Sheldon 1991, Zaborski 2002). In
our laboratory trials, B. cf. vagum showed no predatory behavior toward any
2007 P.K. Ducey, M. McCormick, and E. Davidson 455
arthropods (isopods, millipedes, insects) or earthworms that were offered in
36 trials. Adults of B. cf. vagum did attack and eat most of the snails and
slugs that were offered (Arion spp. and Deroceras sp. eaten in 8 of 9 trials;
Discus sp. eaten in 5 of 6 trials; Helicodiscus sp. eaten in 4 of 6 trials;
Succinea sp. eaten in 4 of 7 trials). Similarly, Jones and Sterrer (2005)
reported that B. vagum in Bermuda fed on snails. In our laboratory, B.
adventitium and B. kewense have refused to attack and eat live members of
these same mollusk species on dozens of occasions over ten years (Ducey et
al., 1999; P.K. Ducey, unpubl. observ.). Similarly, Okochi et al. (2004)
reported that B. kewense on the Ogasawara Islands refused to eat snails.
However, B. cf. vagum is not the only terrestrial planarian known to eat
gastropods. Ogren and Sheldon (1991) found that B. pennsylvanicum would
not prey upon live slugs, but would eat mashed slugs. Other terrestrial
planarians that feed on mollusks include Australopacifica sp. (Okochi et al.
2004), Endeavouria septemlineata Hyman (Mead 1963), Geoplana
burmeisteri Schultz and Muller (Ogren 1995), G. ventrolineata Dendy
(Barker 1989), Platydemus manokwari de Beauchamp (Ogren 1995, Okochi
et al. 2004), and two undescribed species of Bipalium from Japan and islands
in the Pacific (Ogren 1995, Okochi et al. 2004). None of these
molluscivorous terrestrial planarians is distributed within the continental
Predatory behavior of B. cf. vagum
Adults of B. cf. vagum began searching and predatory behavior when
they came in close proximity to a terrestrial mollusk or its mucus trail. Other
terrestrial planarians are also known to follow trails of their prey (Fiore et al.
2005, Mead 1963). During a predatory encounter, B. cf. vagum moved its
head into contact with the mollusk, then crawled upon the prey using body
Table 1. Results of feeding trials with B. cf. vagum as predator.
Mollusks – slugs Annelids – earthworms
Arion spp. Amynthas sp.
Deroceras sp. Aporrectodea turgida
Mollusks – snails Lumbricus rubellus
Discus sp. L. terrestris
Succinea sp. Arthropods – isopods
Arthropods – millipedes
Arthropods – beetle larvae
456 Southeastern Naturalist Vol. 6, No. 3
and head to enwrap it. Whether the prey was a snail or a slug, the flatworm
usually attempted to use its own head to cover the head of the gastropod,
with the effect of greatly reducing escape. A similar capping behavior is
used by B. adventitium to subdue earthworms (Ducey et al. 1999, Fiore et al.
2005) and by Geoplana spp. eating slugs (Froehlich 1955). Wrapping the
prey with the flatworm’s body to some extent is also reported for Geoplana
spp. feeding on mollusks (Froehlich 1955) and for the three other species of
Bipalium in North America eating earthworms (Dindal 1970, Ducey et al.
1999, Fiore et al. 2005, Neck 1987, Ogren and Sheldon 1991, Zaborski
2002). When attacking slugs, B. cf. vagum further reduced prey escape by
sometimes lifting the prey from the substrate during the capping behavior. In
trials with small snail prey (Discus sp. and Helicodiscus sp., 0.02—0.07 g),
the flatworm would completely encircle the shell and position its pharynx
over the aperture. In trials with mid-sized snails (Succinea sp., 0.2—0.9 g),
the flatworm capped the snail’s tentacles and head and wrapped its body
around the muscular foot and shell edge.
The time for completion of the predation attempts varied depending on
the size and species of mollusks involved. Most attacks on slugs appeared to
be slowed, but usually not thwarted, by the mucus secreted by the prey.
Some individuals of the genus Deroceras produced yellow mucus that
inhibited expansion of the pharynx by the flatworms for nearly 30 min. This
occurred despite the flatworm having full control over the slug’s movements.
Ultimately, however, the prey was consumed. The flatworms fed
easily and quickly on the small snails (Discus sp. and Helicodiscus sp.),
sometimes completing attack and consumption in < 3 min. Mid-sized snails
(genus Succinea) escaped in 3 of 7 trials, and in those trials that eventually
led to consumption, the snails escaped and were recaptured several times
before being subdued. The successful attacks occurred when a flatworm was
able to encircle the underside of the shell with its body and cap the snail’s
tentacles with its head and neck. Because we conducted trials only under
laboratory conditions, it remains unclear how often prey would survive these
attacks in nature.
Terrestrial planarians reproduce asexually via fragmentation (= fission),
sexually through the production of egg capsules containing multiple embryos,
or some combination of these methods (Ball and Sluys 1990, Ogren
1984, Winsor 1983). However, the specific reproductive strategy is known
for only a few species (Ducey et al. 2005, Froehlich 1955). In North
America, B. kewense primarily uses fragmentation (Hyman 1943, 1954;
Ogren 1984; Winsor 1983), but rare instances of sexual reproduction in
outdoor populations are known (Connella and Stern 1969, Ducey et al.
2006), whereas B. adventitium reproduces solely via egg capsules (Ducey et
al. 2005, Ogren 1984). One of our B. cf. vagum produced an egg capsule
(approximately 4 mm in diameter) from which 3 offspring hatched (3.0, 5.3,
and 6.3 mg). These offspring had the same pigmentation pattern as the
2007 P.K. Ducey, M. McCormick, and E. Davidson 457
adults, although it took more than a week for the dark markings to fully
appear in the larger individuals. Because of the internal yolk reserves, the
base color of the offspring was lighter than that of the adults. The offspring
eagerly ate mashed slugs. Thus, the reproductive strategy of B. cf. vagum is
similar to that of B. adventitium, which produces similar egg capsules with a
mean of 3.4 offspring per capsule and a mean offspring mass of 5.2 mg
(Ducey et al. 2005).
Bipalium in North America
The individuals of B. cf. vagum described here represent the fourth
species of the genus to be found in North America. Bipalium adventitium
and B. kewense are already widespread and locally abundant throughout
the temperate and subtropical parts of the continent, respectively (e.g.,
Ducey and Noce 1998, Neck 1987, Ogren and Kawakatsu 1998). Because
these two species, and the geographically restricted B. pennsylvanicum,
feed on earthworms, which are important ecosystem engineers, the flatworms
could potentially affect physical and biotic features of agricultural,
horticultural, and natural ecosystems. There is evidence that a terrestrial
planarian that has invaded the British Isles and Faroe Isles—
Arthurdendyus triangulatus (Dendy)—may be having significant impact
on earthworm populations in some areas (Blackshaw and Stewart 1992,
Christensen and Mather 1995).
Although there are other members of the genus that eat mollusks
elsewhere (Ogren 1995, Okochi et al. 2004), B. cf. vagum is the first
mollusk-eating terrestrial planarian with confirmed populations in the
continental United States. With a range that already includes at least parts
of Texas and Florida, this species could potentially have a negative impact
by preying upon rare native snails, as has been reported for other
planarians in the Ogasawara Islands (Okochi et al. 2004). Because there
are no other predators of terrestrial mollusks in North America that have
a predatory archetype (sensu Cox and Lima 2006) similar to Bipalium,
the native land mollusks could be quite vulnerable to this new predatory
species, making ecological impacts more likely (Cox and Lima 2006).
Alternatively, the impact of these planarians would be more complex if
they prey preferentially on invasive snails and slugs. Hopefully, this paper
will alert conservation biologists and land managers to the presence
of this potentially damaging species. Continued monitoring of its geographic
spread and ecological impacts is recommended.
We thank Dan Hodgson and Matt and Grace Donaldson Cormons for allowing us
to study flatworms that they collected, and P.M. Choate for additional information
about the species in Florida. We thank J. Cerqua, C. Fiore, H. Golightly, C. Kalina, T.
Kubinec, G. Shaw, J. Tull, and M. Warner for laboratory assistance.
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