Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Platydemus manokwari
(New guinea flatworm)



Platydemus manokwari (New guinea flatworm)


  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Natural Enemy
  • Preferred Scientific Name
  • Platydemus manokwari
  • Preferred Common Name
  • New guinea flatworm
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Platyhelminthes
  •       Class: Turbellaria
  •         Order: Tricladida
  • Summary of Invasiveness
  • P. manokwari is a large predatory flatworm, originally discovered in New Guinea, which has been deliberately introduced into some Pacific islands in an attempt to control an invasion of the Giant East African S...

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Platydemus manokwari (New guinea flatworm); adult, dorsal aspect.
CaptionPlatydemus manokwari (New guinea flatworm); adult, dorsal aspect.
Copyright©Leigh Winsor
Platydemus manokwari (New guinea flatworm); adult, dorsal aspect.
AdultPlatydemus manokwari (New guinea flatworm); adult, dorsal aspect.©Leigh Winsor
Platydemus manokwari (New guinea flatworm); on an empty shell of the giant African snail, Lissachatina fulica.
CaptionPlatydemus manokwari (New guinea flatworm); on an empty shell of the giant African snail, Lissachatina fulica.
Copyright©Leigh Winsor
Platydemus manokwari (New guinea flatworm); on an empty shell of the giant African snail, Lissachatina fulica.
AdultsPlatydemus manokwari (New guinea flatworm); on an empty shell of the giant African snail, Lissachatina fulica.©Leigh Winsor
Platydemus manokwari (New guinea flatworm); translucent cocoon, with young about to hatch.
CaptionPlatydemus manokwari (New guinea flatworm); translucent cocoon, with young about to hatch.
Copyright©Leigh Winsor
Platydemus manokwari (New guinea flatworm); translucent cocoon, with young about to hatch.
CocoonPlatydemus manokwari (New guinea flatworm); translucent cocoon, with young about to hatch.©Leigh Winsor
Platydemus manokwari (New guinea flatworm); whole specimen, dorsal aspect.
TitleLine drawing of adult
CaptionPlatydemus manokwari (New guinea flatworm); whole specimen, dorsal aspect.
Copyright©Leigh Winsor
Platydemus manokwari (New guinea flatworm); whole specimen, dorsal aspect.
Line drawing of adultPlatydemus manokwari (New guinea flatworm); whole specimen, dorsal aspect.©Leigh Winsor
Platydemus manokwari (New guinea flatworm); (a) dorsolateral aspect showing typical pattern of markings; (b) anterior end showing eyes; (c) ventrolateral aspect showing typical pattern of markings. (Drawings not to scale.)
TitleLine drawing; various aspects
CaptionPlatydemus manokwari (New guinea flatworm); (a) dorsolateral aspect showing typical pattern of markings; (b) anterior end showing eyes; (c) ventrolateral aspect showing typical pattern of markings. (Drawings not to scale.)
Copyright©Leigh Winsor
Platydemus manokwari (New guinea flatworm); (a) dorsolateral aspect showing typical pattern of markings; (b) anterior end showing eyes; (c) ventrolateral aspect showing typical pattern of markings. (Drawings not to scale.)
Line drawing; various aspectsPlatydemus manokwari (New guinea flatworm); (a) dorsolateral aspect showing typical pattern of markings; (b) anterior end showing eyes; (c) ventrolateral aspect showing typical pattern of markings. (Drawings not to scale.)©Leigh Winsor


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Preferred Scientific Name

  • Platydemus manokwari Beauchamp, 1962

Preferred Common Name

  • New guinea flatworm

Other Scientific Names

  • Microplaninae sp. Kawakatsu and Ogren, 1994
  • Platydemus joliveti Beauchamp, 1972
  • Platydemus sp. Winsor, 1980

International Common Names

  • English: rhynchodemid turbellarian; snail-eating flatworm

Summary of Invasiveness

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P. manokwari is a large predatory flatworm, originally discovered in New Guinea, which has been deliberately introduced into some Pacific islands in an attempt to control an invasion of the Giant East African Snail (Barker, 2002), but which has also been accidentally introduced to the soil of other Pacific countries. It has had a significant negative impact on the rare endemic land snail faunas of some Pacific islands, and has become established in a wide variety of habitats.

Presently in Australia, P. manokwari is largely restricted to urban habitats and adjacent human-modified areas. Movement between centres is probably restricted by quarantine measures targeting other pest species, for example restrictions on the movement of banana plants in northern Australia. Spread to native forest is probably largely restricted by the limited availability of a suitable moist habitat in adjacent agricultural areas, and the absence of preferred molluscan prey species.

Molluscs are very uncommon in human-modified habitats in northern Australia. The accidental spread of the species can readily occur. One such transfer of the species in Australia is reported; the flatworm harboured in the hollow tuber of a houseplant Alocasia sent from Cardwell, Queensland, to Weipa, Cape York Peninsula (Waterhouse and Norris, 1987). The invasiveness of the species in some Pacific countries is probably further promoted by the deliberate introduction as a biocontrol agent by humans, and the ready availability of preferred prey, such as Achatina and native mollusc species. The proximity of agricultural land to native forest in these areas may also facilitate the spread of the species. The occurrence of the species in native cloud forest at 675 metres altitude on Pohnpei (Eldredge and Smith, 1994), and in forest at 365 metres altitude on Anatahan Island (Kawakatsu and Ogren, 1994), together with the arboreal habits and fecundity of P. manokwari are particular causes for concern. P. manokwari is included in the 100 worst invasive species in the Global Invasive Species Programme (GISP) Database (

The species was recorded in a hothouse in Caen, France, in 2014 -- the first record in Europe.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Platyhelminthes
  •             Class: Turbellaria
  •                 Order: Tricladida
  •                     Division: Terricola
  •                         Family: Rhynchodemidae
  •                             Subfamily: Rhynchodeminae
  •                                 Genus: Platydemus
  •                                     Species: Platydemus manokwari

Notes on Taxonomy and Nomenclature

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P. manokwari, described by Beauchamp in 1962, was first found at the Dutch New Guinea Agricultural Research Station in the coastal town Manokwari, northwestern Irian Jaya, Indonesia. It is the "rhynchodemid turbellarian" considered to be responsible for the disappearance of the Giant African snail in some parts of Manokwari (Schreurs, 1963; Mead, 1979). The species Platydemus joliveti, collected in 1969 from Pindaude station on Mt Wilhelm, New Guinea, was considered to be a neo-adult P. manokwari by Winsor (1990). Flatworm specimen numbers 2078 and 2080 identified as "Microplaninae sp." from Anatahan Island, Northern Mariana Islands (Kawakatsu and Ogren, 1994), are also considered to be P. manokwari (L Winsor, James Cook University, Townsville, Australia, personal communication, 2004).


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At rest the flatworm is broadest in the middle, tapering to each end. In cross-section, the back is gently convex and the belly is flat. Mature live specimens are approximately 40 mm long and 4 to 5 mm wide. Some specimens may attain a length of 70 mm. The mouth is just behind the mid-point of the belly, with a genital pore about half-way between the mouth and hind end. Two large prominent eyes are situated back from the tip of the elongate snout-like head. The back is light to dark olive-brown, and darkest on either side of the pale creamish-white stripe that runs along the mid-back and at the margins. The olive-brown colour grades to grey at the head end. A thin creamish-white stripe with fine greyish margins runs the length of the body along each side. The belly is creamish-white, with a white mid-ventral stripe. A pale sensory zone passes around the underside of the front end.

Newly emerged hatchlings are up to 8 mm long, with a pale brownish-grey colour extending dorsally and submarginally, a thin pale median dorsal stripe, white ventral surface, and prominent eyes.

A general account of the anatomy of a terrestrial flatworm is provided by Winsor et al. (2004), and detailed anatomical data for P. manokwari are provided by Winsor (1990, 1998d), and Kawakatsu et al. (1992).



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The flatworm occurs in the following areas:

- Australia: Queensland: Lockhart River and Weipa on Cape York Peninsula, Atherton Tablelands, Cairns, Cardwell, Mission Beach, Crystal Creek, Townsville (Winsor, 1990, 1997, 1998c, 1999); Northern Territory: Anula (L Winsor, James Cook University, Townsville, Australia, personal communication, 2004);

- Federated States of Micronesia: Pohnpei (Eldredge and Smith, 1994), Ahatahan (Kawakatsu and Ogren, 1994);

- USA: Hawaii: Oahu (Eldredge and Smith, 1994);

- Indonesia: Irian Jaya: Manokwari (Beauchamp, 1962);

- Japan: Honshu: absent (no P. manokwari has been found in the field.); Ryukyu Islands: Okinawa Island, Miayako Island, and Kumejima Island (Kawakatsu et al., 1993); Ogasawara (Bonin) Islands: Chichijima Island (Kawakatsu et al., 1999);

- Maldives: Fua Mulaku;

- French Polynesia: Mangareva Island (Winsor, 1999);

- Mariana Islands: Aguigan, Guam, Saipan, Rota, Tinian (Eldredge and Smith, 1994);

- Papua New Guinea: Kainantu (Winsor, 1990), Mt Wilhelm (Beauchamp, 1972);

- Palau: Babeldoab, Koror, Ulong (Eldredge and Smith, 1994);

- Philippines: Bugsuk, Manilla (Muniappan et al, 1986);

- Samoa: Alafau and Upolu (Purea et al, 1998);

- Tonga: (Anon., 2002);

- Vanuatu: (Anon., 2002);

- Fiji (Brodie et al., 2012, 2014);

- France: one report from Caen, Normandy (Justine et al., 2014).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes


IndonesiaPresentPresent based on regional distribution.
-Irian JayaPresentNative Invasive Beauchamp, 1962
JapanPresentPresent based on regional distribution.
-Bonin IslandPresentIntroduced Invasive Kawakatsu et al., 1999; Ohbayashi et al., 2005; Sugiura et al., 2006Only Chichijima Island
-HonshuAbsent, formerly presentIntroduced Not invasive Waterhouse and Norris , 1987; Kawakatsu and et al. , 1993
-Ryukyu ArchipelagoWidespreadIntroduced Invasive Kawakatsu and et al. , 1993
MaldivesPresentIntroduced Invasive Muniappan , 1987
PhilippinesPresentIntroduced Invasive Muniappan and et al. , 1986; Waterhouse and Norris , 1987; Muniappan , 1990

North America

USAPresentPresent based on regional distribution.
-HawaiiWidespreadIntroduced Invasive Eldredge and Smith , 1994


FrancePresent, few occurrencesIntroducedJustine et al., 2014Found in a hothouse in Caen, Normandy


AustraliaPresentPresent based on regional distribution.
-Australian Northern TerritoryPresentIntroducedJustine et al., 2014
-QueenslandWidespreadIntroduced Invasive Winsor , 1998c; Waterhouse and Norris , 1987; Winsor , 1990; Winsor , 1997; Winsor , 1999
FijiLocalisedIntroduced Invasive Brodie et al., 2012; Brodie et al., 2014Rotuma island
French PolynesiaPresentIntroduced Invasive Winsor , 1999
GuamWidespreadIntroduced Invasive Muniappan , 1990; Hopper and Smith , 1992
Micronesia, Federated states ofWidespreadIntroduced Invasive Eldredge and Smith , 1994; Kawakatsu and Ogren , 1994
Northern Mariana IslandsWidespreadIntroduced Invasive Eldredge and Smith , 1994
PalauWidespreadIntroduced Invasive Eldredge and Smith , 1994
Papua New GuineaPresentNative Invasive Beauchamp, 1972; Winsor , 1990; Winsor , 1999
SamoaPresentIntroduced Invasive Purea and et al. , 1998
TongaPresentIntroduced Invasive Anon., 2002
VanuatuPresentIntroduced Invasive Anon., 2002

History of Introduction and Spread

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P. manokwari is considered to be native to New Guinea (Waterhouse and Norris, 1987; Winsor, 1990). It was first discovered in 1962 at the Agricultural Research Station in Manokwari, Irian Jaya, with subsequent reports of the species from Mt Wilhelm (1969) and near Goroka (1973).

Eldredge and Smith (1994) provide an overview of the spread of the flatworm to islands in the Pacific. P. manokwari was found in 1976 in Townsville, Queensland, Australia (L Winsor, James Cook University, Townsville, Australia, personal communication, 2004). In Guam, the species was first observed in 1977 and by 1980 it had spread throughout much of the island. The flatworm was established in Saipan by 1981, and reported from Tinian in late 1984; Rota in late 1988, and Aguijan in late 1992. It was deliberately introduced as a bio-agent from Guam to Bugsuk in the Philippines in 1981 (Muniappan et al., 1986), and to the Maldives (Malé, Kurumba and Fua Mulaku) in mid-1985 (Muniappan, 1987). P. manokwari was found in a garden in Manilla in 1985. In 1985, some 200 specimens of the flatworm were sent from Bugsuk to Yokahama, Japan, where they were held in strict quarantine and used solely for laboratory experimental purposes after which they were preserved (Kawakatsu et al., 1992). The flatworm was found in the Okinawa and Ogasawara Islands (Ryû Kyû Islands) in 1990, and from examination of earlier collections it was determined that the flatworm had probably been accidentally introduced in the period 1970 to 1980 (Kawakatsu et al., 1993). It was next reported from Koror, Palau (1991) and at Ulong in 1992; Oahu, Hawaii (1992); Anatahan (1992) and Pohnpei (1993) in the Federated States of Micronesia; Mangareva (1997) in French Polynesia; Upolu, Samoa (1997); Tonga (2002), Vanuatu (2002); and Anula, Northern Territory, Australia (2003). Interestingly the flatworm is present in Tonga, although Achatina is not present in Tonga (Anon., 2002), suggesting accidental introduction. It was reported from Rotuma island, Fiji, in 2012 (Brodie et al., 2012, 2014).

The first report outside the Pacific region, apart from the Maldives, was from a hothouse in Caen, France, in 2013 or 2014 (Justine et al., 2014).


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The natural habitat of the species is undisturbed sub-alpine forest and grasslands. P. manokwari prefers moist but not wet habitats. In human-modified areas, its typical microhabitat includes rotting vegetation, leaf litter, potted plants, beneath fallen timber, and within the leaf bases and cavities of banana rhizomes, palms, taro, and other tuberous plants. After heavy rain, the species may crawl up building walls, entering dwellings via external openings, especially in damp areas such as laundries, bathrooms and toilets. It has been observed preying on native molluscs at heights above 1 metre in trees (Eldredge and Smith, 1994).

Habitat List

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Terrestrial – ManagedCultivated / agricultural land Secondary/tolerated habitat Harmful (pest or invasive)
Protected agriculture (e.g. glasshouse production) Present, no further details
Managed forests, plantations and orchards Principal habitat Harmful (pest or invasive)
Industrial / intensive livestock production systems Present, no further details
Rail / roadsides Present, no further details
Urban / peri-urban areas Present, no further details
Terrestrial ‑ Natural / Semi-naturalNatural forests Principal habitat Harmful (pest or invasive)

Hosts/Species Affected

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The species occurs naturally on Mt Wilhelm at 3625 metres altitude and at Kainantu in the eastern highlands of New Guinea, Irian Jaya. The natural range of this upland species has not yet been determined.

In addition to hosts listed in the Host table of this datasheet, P. manokwari has been reported to prey on the following in the laboratory: Acusta despecta sieboldiana, Bradybaena similaris, Euhadra amaliae callizona, Euhadra peliomphala, Euhadra quaesita, Trishoplita conospira, Satsuma japonica, Euphaedusa tau, Pinguiphaedusa hakonensis, Zaptychopsis buschi, Discus pauper, Helicarion sp., Pythia scarabaeus, Zonitides arboreus (Kaneda et al., 1990), and Partula radiolata (Hopper and Smith, 1992). P. manokwari also preys on a pheretimoid earthworm in north Queensland, Australia.

P. manokwari feeds on live land snails of an endemic species of the Ogasawara Islands, Japan (Mandarinaaureola) under laboratory conditions (Okochi et al., 2004). P. manokwari also feeds on live snails of the predatory species Euglandinarosea as well as other snail and slug species (Ohbayashi et al., 2005). Furthermore, P. manokwari feeds on dead earthworms, and thus can survive in areas where snails have been absent since their invasion (Ohbayashi et al., 2005; Sugiura et al., 2006). P. manokwari feeds on live flatworms of other species (Ohbayashi et al., 2005).

Biology and Ecology

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P. manokwari has a chromosome complement of 2n=12, comprising two pairs of metacentric, three pairs of submetacentric, and a single pair of subtelocentric chromosomes (Oki et al., 1988; Winsor, 1990; Kawakatsu et al., 1993).

Food and Feeding

Like most terrestrial flatworms, P. manokwari is a nocturnal hunter. Emerging at dusk, it is most numerous between 20.00 h and 23.00 h as the humidity increases. In Guam, the species was seen mostly on rainy nights. The flatworm detects prey using sensory pits located on the underside of the tip of the head. The large eyes suggest vision plays a part in prey capture, noted in other family members. Flatworms are attracted to molluscan slime trails. Once they reach the snail, they glide over the shell and body and get into the pneumostome and pallial cavity where they then feed on the internal organs (Mead, 1979). P. manokwari can overwhelm prey by sheer numbers. Numerous specimens are frequently observed feeding on a single prey; behaviour also seen in geoplanid terrestrial flatworm species of the genera Lenkunya, Parakontikia and Kontikia. When the prey is over-run, the flatworm protrudes a cylindrical feeding tube (pharynx) through the mouth located on the belly. The feeding tube is forced into the prey partly by muscular action and partly assisted by powerful enzymes secreted from the tip of the tube. The enzymes digest the prey's tissues and this food passes to the flatworm via the feeding tube. Small prey is swallowed whole.

P. manokwari appears to be an opportunistic carnivore and generally unselective in choice of prey (Waterhouse and Norris, 1987). It is a well-documented predator of the Giant African snail, Achatina fulica (Mead, 1979; Muniappan, 1990). However, Cowie (2000) considers that the evidence for the role of the flatworm in the decline of Achatina populations is only correlative, not convincingly causative. P. manokwari has been observed feeding on both juvenile and adult partulid snails at heights above 1 metre in trees, and in captivity the flatworm fed on Partula and Pythia specimens (Hopper and Smith, 1992; Eldredge and Smith, 1994). In Australia, P. manokwari was observed feeding on a variety of small invertebrate animals such as earthworms (Pheretima sp.) and cockroaches (Calolampra spp.). In captivity, P. manokwari fed on native geoplanid planarians (Caenoplana sp.) and native molluscs (Fastosarion sp. and Physastra sp.), although in a limited trial it refused offered specimens of the veronicellid slugs, Vaginulus plebeius and Laevicaulis alte (L Winsor, James Cook University, Townsville, Australia, personal communication, 2004). The flatworm has also been reported feeding on a moribund green tree frog, Litoria caerulea and chop bones in areas where pets are fed (Waterhouse and Norris, 1987). Land snails in the Ryû Kyû Islands on which P. manokwari preys, include Bradybaenidae (five species), Camaenidae (three species), Clausiliidae (two or more species), Cyclophoridae (two species), and Trochomorphidae (two species) (Kaneda et al., 1990; Kawakatsu et al., 1993). For laboratory rearing of P. manokwari, the land snail Bradybaena similaris proved more suitable as a food source than Limax marginatus (Kaneda et al., 1992).

Reproductive Biology

P. manokwari reproduces sexually throughout its geographic range. If the flatworm is divided into several pieces, each piece regenerates into complete animals in 2 weeks (Kaneda et al, 1990); regenerative behaviour observed in all triclads. However, there is no evidence in P. manokwari of asexual reproduction by fission (architomy), in which a hind portion of the body is shed within 24 hours of feeding; the shed portion regenerating into a whole worm (Winsor, 1990). Oviposition occurs through the gonopore approximately 4 days post-copulation. Copious amounts of mucus from the viscid gland are discharged during oviposition and adhere the cocoon to the substratum (Winsor, 1998b, d). Freshly oviposited cocoons are 2 to 5 mm in diameter. They are opaque lemon to light-tan and darken on exposure to the air due to quinnone or similar tanning mechanisms (Winsor, 1990). The sclerotin from which the cocoon is formed is rich in tryptophane, the hydrophobicity of which may protect the embryos from desiccation (Winsor, 1990, 1998b). Cocoon size is related to both the specimen size and to the number of cocoons laid by an individual resulting from a single insemination. Large cocoons are produced by large individuals, and small cocoons by small specimens. In each case, the first cocoon laid is the largest of those produced following a single insemination. Thereafter the cocoon size and number of embryos in each cocoon progressively decrease (Winsor, 1990).

The cocoons have a banded appearance approximately 7 days following oviposition, because of the lightly pigmented embryos that are clearly visible through the now translucent cocoon wall. Approximately three to nine young are present in each cocoon. At this stage, the embryos are motile and their eyes are conspicuous. Approximately 10 days after the cocoon is laid, the hatchlings emerge through an axial split in the cocoon wall (Winsor, 1990).

Under experimental conditions, the optimum temperature for rearing P. manokwari in terms of pre-oviposition period and cocoon production was 24°C. The mean weight of flatworms was between 0.55 and 0.95 g at first oviposition, and mean post-oviposition developmental period for the young to hatch from the cocoon was 7.8 ± 1.2 days (Kaneda et al., 1992). Each cocoon contained an average of 5.2 juveniles (3 to 9) (Kaneda et al., 1990). The flatworm begins oviposition within 3 weeks of hatching (Kaneda et al., 1990). The temperature threshold for oviposition lies between 15 and 18°C (Kaneda et al., 1992). Kaneda et al. (1990, 1992) provide methods for rearing P. manokwari in the laboratory.

Environmental Requirements

In north Queensland, P. manokwari first appears with the onset of good soaking rains, generally from late December onwards. Populations gradually increase during the monsoon season reaching greatest numbers towards the end of February and March. Numbers gradually diminish with the progression of the dry season, and the flatworm migrates to moist areas deeper within the soil. However, in well-watered habitats the species is present in small numbers throughout the year. The specific moisture requirements of the species have not been determined.


P. manokwari is often found with other introduced or vagrant flatworm taxa such as Bipalium kewense, Caenoplana coerulea, Caenoplana sp. and Rhynchodemus sp.


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A - Tropical/Megathermal climate Preferred Average temp. of coolest month > 18°C, > 1500mm precipitation annually
Af - Tropical rainforest climate Preferred > 60mm precipitation per month
Am - Tropical monsoon climate Preferred Tropical monsoon climate ( < 60mm precipitation driest month but > (100 - [total annual precipitation(mm}/25]))
Cf - Warm temperate climate, wet all year Tolerated Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year

Air Temperature

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Parameter Lower limit Upper limit
Mean annual temperature (ºC) 20
Mean minimum temperature of coldest month (ºC) 16

Notes on Natural Enemies

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The natural enemies of P. manokwari are unknown. Natural enemies of terrestrial flatworms in general include the larvae of mycetophilid flies (Planarivora insignis) and gregarines.

Means of Movement and Dispersal

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Natural Dispersal

P. manokwari is a highly mobile and swiftly moving flatworm. The success, extent and rapidity of dispersal of the species, unaided by humans, are largely dependent upon the availability of microhabitat and moisture in the area. In an urban garden in Townsville, Australia, the species took 1 year to colonize mixed garden habitats separated by 20 to 30 metres of lawn (Winsor, 1990). However, on Fua Mulaku (Maldives), P. manokwari cleared Achatina for a radius of 180 metres from the release sites within approximately 1 year (Muniappan, 1987).

Agricultural Practices

It is highly probable that farmers intentionally and unofficially spread P. manokwari for use as a biocontrol agent against Achatina in agricultural areas. The flatworm is currently used as a biocontrol agent in Samoa and Vanuatu (Anon., 2002).

Movement in Trade

The species was probably accidentally transported together with live plant material such as banana plants. Cocoons, juveniles and adults may be transported on stems/shoots/trunks/branches; bulbs/tubers/corms/rhizomes; wood without bark; bark; and/or growing medium accompanying plants (see Trade table).

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Biological controlFor biocontrol of giant African snails Yes Yes Muniappan , 1987; Muniappan , 1990
Nursery tradeP. manokwari can be readily transported in soil on potted plants Yes Yes Sugiura, 2008

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Machinery and equipmentP. manokwari can be readily transported in soil on machines Yes
Plants or parts of plants Yes
Soil, sand and gravelP. manokwari can be readily transported in soil on potted plants Yes Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bark Yes Pest or symptoms usually visible to the naked eye
Bulbs/Tubers/Corms/Rhizomes Yes Pest or symptoms usually visible to the naked eye
Growing medium accompanying plants Yes Pest or symptoms usually invisible
Stems (above ground)/Shoots/Trunks/Branches Yes Pest or symptoms usually visible to the naked eye
Wood Yes Pest or symptoms usually visible to the naked eye

Wood Packaging

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Wood Packaging not known to carry the pest in trade/transport
Loose wood packing material
Processed or treated wood
Solid wood packing material with bark
Solid wood packing material without bark

Impact Summary

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Animal/plant collections None
Animal/plant products None
Biodiversity (generally) Negative
Crop production Positive
Environment (generally) Negative
Fisheries / aquaculture None
Forestry production None
Human health None
Livestock production None
Native fauna Negative
Native flora None
Rare/protected species Negative
Tourism None
Trade/international relations Negative
Transport/travel None

Economic Impact

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P. manokwari has a positive economic impact in controlling the Giant African snail, Achatina fulica. The reduction of 95% of the population of Achatina in Guam resulted in large quantities of snail bait left unsold, with an estimated annual saving for the people of Guam of US$100,000 on snail bait, and over US$500,000 in direct crop losses (Muniappan, 1983b). In Bugsuk Island in the Philippines, Achatina was causing severe damage to cover crops of Pueraria sp. and Centrosema sp. grown beneath coconut trees. In 1982, hand picking Achatina from the 1600 ha plantation and dumping in the ocean cost US$60,000; little impact was made on the snail population. Introduction of P. manokwari in late 1981 and early 1982 resulted in successful suppression of the Achatina population by September 1983 (Muniappan et al., 1986).

Environmental Impact

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P. manokwari has impacts on native and endemic land snails. For example, over 90% of ground-dwelling land snails experimentally placed on Chichijima (Ogasawara Islands) for 11 days were eaten by P. manokwari (Sugiura et al., 2006). A rapid decline of endemic land snails was caused by P. manokwari on Chichijima (Ohbayashi et al., 2007). Cowie and Robinson (2003) report that the flatworm is a serious threat to the native snail fauna on Samoa. This flatworm is also the likely cause of extinctions of native and introduced gastropods on Guam and may be the most important threat to the Mariana Partulidae (Hopper and Smith, 1992).

Threatened Species

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Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Eua zebrina (Tutuila tree snail)EN (IUCN red list: Endangered) EN (IUCN red list: Endangered); USA ESA listing as endangered species USA ESA listing as endangered speciesAmerican SamoaPredationUS Fish and Wildlife Service, 2014a
Ostodes strigatus (sisi snail)USA ESA listing as endangered species USA ESA listing as endangered speciesAmerican SamoaPredationUS Fish and Wildlife Service, 2014b
Partula langfordi (Langford's tree snail)USA ESA listing as endangered species USA ESA listing as endangered species; CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered)Northern Mariana IslandsPredationUS Fish and Wildlife Service, 2015

Social Impact

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P. manokwari invasion can affect human health, because P. manokwari is a paratenic host of the nematode Angiostrongylus cantonensis which causes ‘angiostrongyliasis’ (Asato et al., 2004). Fresh vegetables contaminated with infected P. manokwari can be a source of human infection (Asato et al., 2004).


Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Is a habitat generalist
  • Capable of securing and ingesting a wide range of food
  • Highly mobile locally
  • Long lived
  • Fast growing
  • Has high reproductive potential
  • Reproduces asexually
Impact outcomes
  • Negatively impacts human health
  • Reduced native biodiversity
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
Impact mechanisms
  • Pest and disease transmission
  • Interaction with other invasive species
  • Predation
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Highly likely to be transported internationally illegally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult/costly to control


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The impact of the flatworm on populations of Achatina, and consideration of the flatworm as a possible control agent for the Giant African snail (Achatina fulica) was first noted in Manokwari, Irian Jaya (Schreurs, 1963; Mead, 1979). In 1977, P. manokwari was discovered on Guam and by 1980 on much of the island, reducing the Giant African snail population by 95% (Waterhouse and Norris, 1987). Transfer of the flatworm from Guam to Bugsuk in the Philippines in 1981 (Muniappan et al., 1986), met with similar success in reducing Achatina to the status of a minor pest. In Saipan and the Maldives, control of the Giant African snail was achieved in approximately 15 months at sites where the flatworm was released (Muniappan, 1987). P. manokwari has subsequently been introduced accidentally, and deliberately and possibly unofficially as a biocontrol agent to locations outside its natural range.

Uses List

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  • Biological control


Top of page Specimens from widely separated locations exhibit remarkable uniformity in external and internal characters, and the species is generally readily distinguishable from other platydemid flatworms. A positive identification of the species is made on the basis of internal anatomical features, in particular the anatomy of the copulatory apparatus, revealed following histological examination of preserved specimens. Winsor (1998a) provides technical procedures for the collection, preservation and histological examination of terrestrial flatworms.

Detection and Inspection

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Terrestrial flatworms are normally detected by day by hand picking in moist microhabitats. Flatworms emerge at night to hunt and can be found with the aid of a spotlight or headlamp. Trapping methods for flatworms include laying plantain leaves or small boards directly on the ground; wetting areas of dry soil and covering these with a damp board (Ogren, 1955); or using a ceramic tile backed with 5 mm of polystyrene placed tile-down on the ground (Blackshaw, 1990). Polythene bags, 22 cm², and each filled with 1.5 kg of sand, were used to provide an artificial habitat to trap flatworms in New Zealand (Yeates et al., 1998), and conventional pitfall traps were successfully used in Tasmania to trap flatworms in a button grass habitat. Terricola can be extracted from soil samples using a 100 watt light bulb as a heat source (Ogren, 1955), but generally are not collected from soil or litter using dry extraction methods such as Berlese-funnel extractors. Extracting Terricola from soil samples using wet extractors such as those of Macfayden or Kempson (in Southwood, 1966) have potential, but appear not to have been reported. On-site formalin extraction (application rate of 4.5 litres of 0.2% formaldehyde per 1.2 m² quadrat, after Raw, 1959) was effective to a depth of at least 30 cm; the irritant bringing to the surface all specimens of a soil-dwelling flatworm species (Blackshaw and Stewart, 1992).

Bait traps can be useful for the detection of P. manokwari. Sugiura et al. (2006) placed land snails in 2-mm mesh nylon bags (approximately 30 x 25 cm) that allowed the entry of P. manokwari but not the escape of the snails. Five live land snails were placed as bait in each bag. When they checked bags three days after placement, they could find P. manokwari invading bags.

Similarities to Other Species/Conditions

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Extremes in the density of dorsal pigmentation may cause P. manokwari to be confused with Platydemus bivittatus recorded from Milne Bay, New Guinea, and Platydemus quadristriatus from the Tonga Islands. Specimens with heavily pigmented dorsal stripes, as may occur in old individuals, could approach the external appearance of P. bivittatus, but would lack the fine dark median pre-ocular stripe present in the latter species. Also the distance between the mouth and gonopore in P. bivittatus is considerably less than in a similar sized specimen of P. manokwari. The two species can be readily distinguished on the basis of their internal anatomy.

Similarly, specimens of P. manokwari in which only the margins of the brown dorsal stripes are evident on a lighter ground colour (as in a specimen from Lockhart River, Queensland, Australia) approach P. quadristriatus, although may be distinguished from this species by a pale dorsal median stripe present in P. manokwari.

Prevention and Control

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Phytosanitary Measures

A hot water treatment is used as a quarantine measure for terrestrial flatworms. This method may be successful in controlling transmission via live plants of other threatening flatworm species such as P. manokwari.

The portion of the plant contained within soil is first sealed in a plastic bag. The bagged portion is then immersed in hot water at 34°C for 5 minutes. This treatment kills the adult New Zealand flatworm (Artioposthia triangulata [Arthurdendyus triangulatus]). Research to check the effect of heat on egg capsules is in progress (Murchie and Moore, 1998).

Hot water tolerance of P. manokwari has been reported, but Sugiura (2008) reports that immersion in water at ≥ 43°C for 5 min) kills P. manokwari.

Early Warning Systems

Essential measures include quarantine checks and good hygiene of incoming and outgoing consignments and standing stocks of potted and other germinated plant material, setting flatworm traps, and identification of any captured flatworms.

Biological Control

Biological control of flatworms is in its infancy, and there are no immediate prospects of widely applicable control methods.



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31/03/2008 Updated by:

Shinji Sugiura, Department of Forest Entomology, FFPRI, 1 Matsunosato, Tsukuba, Ibaraki, 305-8687, Japan

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