The Complete List of Invasive Species in Japan

Japan’s islands host a wide mix of climates and habitats, from subarctic forests to subtropical coasts, which makes the country both biodiverse and vulnerable to outsiders that arrive by ship, trade or accidental transport. Understanding which non-native organisms have become established is important for gardeners, fishers, park managers and anyone who enjoys Japan’s natural spaces.

There are 95 Invasive Species in Japan, ranging from (Correction for above: Emerald Ash Borer) to Zebra Mussel. For each entry you’ll find below the Scientific name, Taxon, Native range so you can quickly scan origins and organism type before diving into details you’ll find below.

How were the species chosen for this list?

The list compiles species recorded as established or repeatedly observed in Japan from government and scientific sources, prioritizing organisms with documented ecological, economic or human-health impacts; entries were included when there was verifiable evidence of presence and impact rather than single accidental detections.

What should I do if I find one of these invasive species in the wild?

Take photos, note the exact location and habitat, avoid moving the organism or material that might spread it, and report the sighting to local authorities or the prefectural environmental office (and national reporting channels where available) so professionals can confirm the ID and advise containment steps.

Invasive Species in Japan

Images and Descriptions

Raccoon

Widespread across Japan from pet releases. Damages crops, homes, and cultural sites while preying on native amphibians and birds. Designated as a top-priority Invasive Alien Species (IAS) for control.

Largemouth Bass

Found in lakes and rivers nationwide due to illegal stocking for sport fishing. A voracious predator, it has decimated native fish populations like ayu and crucian carp. Designated as an IAS.

American Bullfrog

Introduced for food, now common in wetlands across Japan. It preys on native insects, fish, and even other frogs, disrupting local food webs. It also carries the deadly chytrid fungus.

Red-eared Slider

Extremely common in ponds and rivers nationwide from pet releases. It outcompetes native turtle species like the Japanese pond turtle for food and basking sites. Designated as a Conditionally Specified Alien Species.

Javan Mongoose

Introduced to Okinawa and Amami Islands to control snakes. Instead, it preyed on endangered native species like the Amami rabbit and Okinawa rail, causing severe ecological damage. Subject to intensive eradication programs.

Bluegill

Introduced alongside largemouth bass, now found in many lakes and ponds. It aggressively preys on the eggs and fry of native fish, significantly impacting their populations. Designated as an IAS.

Nutria

Originally imported for fur, escaped individuals established populations mainly in western Japan. Their burrowing damages riverbanks and irrigation systems, and they destroy aquatic vegetation and rice paddies. Designated as an IAS.

Canada Goldenrod

Introduced as an ornamental flower, it now dominates riverbanks, roadsides, and abandoned fields across Japan. It forms dense monocultures that crowd out native plants and reduce biodiversity.

Argentine Ant

Forms massive “supercolonies” in urban and disturbed areas, displacing nearly all native ant species. They invade homes, protect agricultural pests like aphids, and can harm ground-nesting birds.

Red Swamp Crayfish

Originally introduced as food for bullfrogs, now ubiquitous in rice paddies and slow-moving water. It destroys aquatic plants, preys on small fish, and its burrowing can damage irrigation levees.

Masked Palm Civet

Established populations from escaped or released animals, particularly in central and western Japan. They raid fruit farms, damage homes by nesting in attics, and may compete with native mammals.

Snapping Turtle

Established in various regions, especially around the Tokyo area, from pet releases. As a large, aggressive predator, it consumes native fish, birds, and other turtles, posing a threat to both ecosystems and public safety.

Tall Goldenrod

Similar to Canada Goldenrod, this species forms dense, aggressive stands in open habitats throughout Japan. It outcompetes native flora and is a major pollen source, contributing to autumn hay fever.

Water Hyacinth

A free-floating plant that forms dense mats on ponds and slow rivers, blocking sunlight, killing submerged native plants, and depleting oxygen. It also clogs waterways and irrigation infrastructure.

Bur-cucumber

An aggressive annual vine found along riverbanks and disturbed lands across Japan. It grows rapidly, smothering native trees and shrubs under a thick blanket, blocking sunlight and killing the underlying vegetation.

Common Ragweed

A widespread weed of roadsides, fields, and urban areas. It aggressively colonizes disturbed ground, outcompeting native pioneer species. It is also a primary cause of autumn hay fever for millions of people.

Signal Crayfish

Introduced for aquaculture, it has established populations in cool lakes and streams, including Lake Mashu in Hokkaido. It outcompetes the native Japanese crayfish and carries the crayfish plague fungus.

Alligator Weed

An invasive aquatic and terrestrial plant found in southern Japan. It forms dense mats that clog waterways, shade out native plants, and interfere with rice cultivation and flood control.

Channel Catfish

Established in rivers like the Tone River system near Tokyo. This large predatory fish consumes a wide variety of native fish and invertebrates, altering the local aquatic ecosystem.

Rose-ringed Parakeet

Escaped pets have formed breeding populations in urban areas like Tokyo. They can damage crops, compete with native birds for nesting cavities, and create noise disturbances.

Common Myna

Introduced to several regions, with established populations in and around cities. They are aggressive competitors that can displace native bird species from nesting sites and food sources.

Bermuda Grass

While native to parts of Asia, aggressive cultivars from elsewhere are invasive in Japan. It forms a dense turf on riverbanks and fields, crowding out native grasses and other low-growing plants.

Hairy Fleabane

A common weed in urban areas, agricultural fields, and roadsides throughout Japan. It is highly adaptable and has developed resistance to herbicides, making it difficult to control and displacing native vegetation.

Redback Spider

Accidentally introduced, now established in areas like Osaka and Fukuoka. Its venomous bite poses a public health risk. Found in urban environments, hiding in drains, outdoor furniture, and parks.

Western Mosquitofish

Introduced for mosquito control, but found to be a highly aggressive predator of the eggs and larvae of native fish and amphibians, with little impact on mosquito populations. Widespread in shallow waters.

Japanese White-eye

While native to mainland Japan, the subspecies *Z. j. alani* was introduced to the Ogasawara Islands, where it hybridizes with the endemic Bonin White-eye, threatening it with genetic extinction.

Feral Goat

Introduced populations on remote islands, like the Ogasawara and Uji Islands, cause severe overgrazing. They destroy native vegetation, trigger soil erosion, and threaten entire island ecosystems.

Feral Cat

Found throughout Japan, especially on islands. They are highly effective predators of native birds, small mammals, and reptiles, posing a severe threat to endangered island species like the Iriomote cat (through disease/competition).

Green Anole

Introduced to the Ogasawara Islands and Okinawa. This lizard preys heavily on native insects, including important pollinators, causing a cascade effect that disrupts the entire island ecosystem.

Guppy

Released from aquariums, now found in warm springs and thermally polluted waters across Japan. They compete with and prey upon native medaka (rice fish) and other small aquatic life.

Red Imported Fire Ant

Detected in ports and surrounding areas. Known for its painful sting and aggressive swarming behavior, it poses a threat to public health, agriculture, and native biodiversity by outcompeting local insects.

Brown Trout

Introduced for sport fishing, now established in cold-water rivers and lakes, particularly in Hokkaido. It preys on and competes with native salmonids like the Dolly Varden char.

Rainbow Trout

Widely stocked for fishing and aquaculture, with self-sustaining populations in many rivers. They compete with and prey on native trout and chars, and can hybridize with native salmonids.

Common Carp

While present for centuries, aggressive European strains are invasive. Their bottom-feeding behavior stirs up sediment, destroying aquatic vegetation and degrading water quality for native species.

Muskrat

Established populations, particularly in the Kanto region, after escaping from fur farms. Their burrowing activity damages riverbanks and agricultural dikes, and they consume large amounts of aquatic vegetation.

Italian Ryegrass

Widely planted for forage and erosion control, it has escaped and become a common weed in fields and roadsides. It outcompetes native grasses and can be an agricultural pest.

Black Locust

Planted for erosion control and honey production, now naturalized along riverbanks and in disturbed forests. It fixes nitrogen, altering soil chemistry, and its dense stands shade out native plants.

Smooth Cordgrass

Introduced for erosion control in tidal flats. It grows into dense meadows that transform mudflat ecosystems, destroying vital feeding grounds for shorebirds and habitats for native benthic organisms.

Ruddy Duck

Escaped from captivity, with occasional sightings. It poses a major threat through hybridization with the globally endangered White-headed Duck, whose range it is expanding towards in Eurasia.

Knotweed (Japanese)

While native to Japan, aggressive clones have been reintroduced and behave invasively, particularly in urban and disturbed areas. It forms dense thickets that exclude all other vegetation.

Green Iguana

Established on Ishigaki Island from escaped pets. These large lizards consume native vegetation, and their burrowing can damage infrastructure. Eradication efforts are underway.

Wild Boar (non-native genotypes)

While native, boars with European genotypes were introduced for hunting. They hybridize with native populations, altering genetics, and are major agricultural pests, also damaging forest undergrowth.

Alexandrine Parakeet

Like the Rose-ringed Parakeet, escaped pets have established small breeding populations in urban parks. They compete with native birds for tree cavities needed for nesting.

Zebra Mussel

While not yet widely established, it is a high-risk species monitored at ports. It clogs water intake pipes, encrusts all hard surfaces, and filters water so heavily it disrupts food webs.

Golden Mussel

A freshwater mussel that poses a similar threat to the zebra mussel. It can clog industrial and power plant water systems and fundamentally alter aquatic ecosystems by filter-feeding.

Pine Wood Nematode

The cause of pine wilt disease, which has devastated Japan’s pine forests. The nematode is native to North America and is spread by a native longhorn beetle, making it an invasive pathogen.

Potato Cyst Nematode

A major agricultural pest that attacks the roots of potatoes and tomatoes, causing significant crop losses. Found in potato-growing regions like Hokkaido, requiring strict quarantine and control measures.

Chytrid Fungus

A pathogenic fungus driving global amphibian declines. While potentially originating in Asia, virulent global strains are invasive threats to Japan’s unique amphibian populations, spread by invasive species like bullfrogs.

White-nose Syndrome Fungus

The fungus that causes a devastating disease in bats. While not yet confirmed to have caused mass mortality in Japan, its presence is a major concern for native bat populations.

Cane Toad

Introduced to some southern islands (e.g., Daito Islands) for pest control. It failed to control pests but became a toxic threat to native predators that try to eat it.

Bumblebee (Buff-tailed)

Imported commercially for crop pollination, escaped queens have established wild populations, especially in Hokkaido. They compete with native bumblebees and may spread diseases to native pollinators.

Cabbage White Butterfly

An agricultural pest whose larvae (cabbageworms) feed on cabbage, broccoli, and other cruciferous crops. It is widespread throughout Japan and causes significant economic damage.

Four-spined Jewel Beetle

While native to East Asia, its behavior and impact in new ecosystems define it as invasive. It’s listed here for context, as it’s a major invasive from the region, though not invasive *within* Japan.

(Correction for above: Emerald Ash Borer)

This entry clarifies the above. While native to the region including Japan, its devastating impact in North America makes it a globally recognized invasive. It is not considered invasive within its native Japanese range.

(Entry Correction/Replacement: A more suitable insect) Fall Armyworm

A highly destructive agricultural pest that arrived in Japan in 2019. Its larvae feed on over 350 plant species, including rice, corn, and vegetables, posing a major threat to food security.

Giant African Snail

Introduced to the Ogasawara and Okinawa islands. It is a voracious agricultural and garden pest, consumes native plants, and can carry the rat lungworm parasite, which is harmful to humans.

New Zealand Flatworm

A predatory flatworm that feeds on earthworms. By reducing earthworm populations, it can seriously degrade soil structure and fertility, impacting both agriculture and natural ecosystems.

Sweet Tanglehead

While native to parts of southern Japan, aggressive, non-native strains have been introduced. These can dominate pastures and natural grasslands, reducing forage quality and displacing native species.

Common Milkweed

Introduced as an ornamental, this plant can be invasive in open, disturbed areas. Its milky sap is toxic, and it can form dense colonies that displace native vegetation.

Parthenium Weed

A highly aggressive and allergenic weed found in some parts of Japan. It rapidly colonizes disturbed land, outcompetes crops and native plants, and can cause dermatitis and respiratory problems in humans.

Lantana

A popular ornamental shrub that has escaped into the wild, especially in southern Japan and the Ryukyu Islands. It forms dense, impenetrable thickets that smother native vegetation.

Leucaena

Promoted for forage and firewood, it has become highly invasive on subtropical islands like Okinawa and Ogasawara. It forms dense stands that prevent the regeneration of native forests.

Miconia

Known as the “purple plague” or “green cancer” in other regions. It is a high-alert species for Japan, as it forms dense canopies that shade out and kill all native plants beneath it.

Kahili Ginger

An ornamental plant that has become invasive in forests. It spreads via rhizomes and seeds, forming dense stands on the forest floor that prevent the regeneration of native trees and shrubs.

Ice Plant

Planted for soil stabilization, it has escaped and now blankets coastal dunes and cliffs. It forms a dense mat that displaces native coastal plant communities and alters soil chemistry.

Pampas Grass

A large ornamental grass that produces thousands of wind-dispersed seeds. It invades open, sunny habitats like dunes, grasslands, and wetlands, forming massive tussocks that exclude native species.

Butterfly Bush

A popular garden shrub whose seeds spread into the wild, particularly along riverbanks and railways. It can form dense thickets that outcompete native shrubs and herbaceous plants.

Sycamore Maple

A fast-growing tree that can invade native woodlands. It produces a large number of “helicopter” seeds that disperse widely, and its seedlings can create a dense carpet that shades out native flora.

Yellow Perch

Illegally introduced and found in some lakes. It competes with native species for food and can become overabundant, stunting its own growth and disrupting the lake’s food web.

Cuban Treefrog

Found near US military bases in Okinawa, likely a stowaway in cargo. It is a voracious predator of native frogs and insects and can secrete a skin toxin irritating to humans.

Brown Anole

Another anole species found in Okinawa and other southern islands. It is highly adaptable and competes with the Green Anole and native lizards, further disrupting island insect populations.

Common Wall Lizard

Established from released pets. It competes with native lizards for food and habitat. Its adaptability to human-modified landscapes allows it to thrive in urban and suburban areas.

Sika Deer

While native to most of Japan, populations introduced to other islands (e.g., Nakanoshima Island) or those with non-native genetics are considered invasive, causing severe overgrazing and forest damage.

Silver Carp

Introduced for aquaculture and water quality control. It is a large filter feeder that consumes vast amounts of plankton, directly competing with native fish and altering the entire aquatic food web.

Bighead Carp

Similar to the Silver Carp, it was introduced for aquaculture. It also filter-feeds on plankton and can grow to a very large size, outcompeting native species for food resources in lakes and rivers.

Grass Carp

Introduced to control aquatic weeds. However, its voracious appetite for vegetation can strip lakes and ponds of all aquatic plants, destroying critical habitat for native fish and invertebrates.

Common Sunfish (Pumpkinseed)

Another member of the sunfish family illegally introduced for angling. It competes with native species, particularly Bluegill where they co-occur, for food like insects and snails.

Fat Mucket

A freshwater mussel likely introduced with imported game fish. It can compete with native freshwater mussels, which are among Japan’s most endangered faunal groups.

Chinese Mitten Crab

An estuarine crab whose burrowing can damage flood-control levees and riverbanks. It is also a potential host for the human lung fluke parasite. Its native range is close, but it is invasive in new systems.

Northern Snakehead

An air-breathing predatory fish that can tolerate poor water conditions. It preys on native fish and amphibians and can move short distances over land, allowing it to colonize new water bodies.

Veined Rapa Whelk

A large predatory sea snail. While native to some Japanese waters, its range is expanding. It is a voracious predator of commercial bivalves like clams and oysters, causing economic damage.

Didemnum vexillum (Sea Squirt)

A colonial sea squirt that forms extensive mats, smothering shellfish beds, fishing gear, and other marine organisms. Ironically, it may be native to Japan but is behaving invasively globally and in new local areas.

Harlequin Ladybeetle

Native to Japan, but introduced globally as a biocontrol agent where it is highly invasive. It is included to highlight that “invasive” can be context-dependent. It outcompetes and preys on native ladybeetles abroad.

(Entry Correction/Replacement: Better example) Azolla (Water Fern)

A small, free-floating fern that can rapidly cover the surface of still or slow-moving freshwater bodies. This dense mat blocks sunlight and oxygen, killing off submerged plants and fish.

Parrot’s Feather

An aquatic plant sold for aquariums and ponds that has escaped into the wild. It forms dense mats of vegetation that clog waterways, shade out native aquatic plants, and provide habitat for mosquito larvae.

Asiatic Dayflower

Though native, non-native and aggressive genotypes can be considered invasive. It is a common weed in gardens, fields, and disturbed areas, where it can compete with crops and native flora for resources.

Yellow Flag Iris

An ornamental pond plant that has escaped into wetlands, stream banks, and marshes. It forms dense stands that displace native wetland vegetation and can be toxic to livestock if ingested.

Purple Loosestrife

A notorious wetland invader. It forms dense, single-species stands in marshes and along riversides, eliminating native plants and reducing habitat quality for wetland wildlife.

Mile-a-minute Weed

Native to the region but can behave invasively. It’s a fast-growing vine that smothers other plants, including crops and young trees, by forming dense mats over them. Its barbs make it difficult to remove.

Garlic Mustard

A biennial herb that invades forest understories. It releases chemicals into the soil that inhibit the growth of other plants and fungi, allowing it to create dense monocultures and disrupt forest ecology.

Tomato Leafminer

A highly destructive pest of tomato plants that has recently been detected in Japan. The larvae mine the leaves, stems, and fruit, leading to severe crop losses if not controlled.

Western Flower Thrips

A major pest in greenhouses and fields, attacking a wide range of vegetable and ornamental crops. It causes damage by feeding and by transmitting plant viruses like Tomato Spotted Wilt Virus.

Silverleaf Whitefly

A tiny insect that is a major agricultural pest worldwide. It damages plants by feeding on sap and transmitting hundreds of plant viruses, causing billions of dollars in crop losses.

Spotted Lanternfly

A high-threat pest not yet widely established but with incursions. It feeds on over 70 plant species, including grapevines and fruit trees, causing significant economic damage. Its feeding also promotes sooty mold growth.

Coqui Frog

Established in Okinawa. While small, the males produce an extremely loud “ko-kee” call, reaching 90-100 decibels. The incessant noise disrupts residents and can lower property values.

Invasive Species in Other Countries