Introduced-species
Guides
Trichoniscus pygmaeus
Least Pygmy Woodlouse
Trichoniscus pygmaeus is a minute terrestrial isopod commonly known as the Least Pygmy Woodlouse. It is native to Britain and Ireland, with a limited introduced distribution in the United States. The species is among the smallest woodlice in its native range, measuring approximately 2.5 mm in length. Its translucent, pinkish-yellow coloration and diminutive size distinguish it from other European woodlice.
Trichonyx sulcicollis
Trichonyx sulcicollis is a small rove beetle (family Staphylinidae, subfamily Pselaphinae) originally described from Europe in 1816. It belongs to the tribe Trichonychini within the diverse ant-loving beetle group (Pselaphinae). The species has been recorded across much of Europe and has been introduced to the northeastern United States (New Hampshire, New York). As a pselaphine rove beetle, it is likely associated with leaf litter and soil habitats, though specific ecological details remain poorly documented.
Trichosirocalus
rosette weevils, crown weevils
A genus of small true weevils native to the Palearctic region. Several species have been widely introduced to North America, Australia, and New Zealand as biological control agents for invasive thistles. The genus was historically treated as containing a single species, T. horridus, but integrative taxonomic studies using molecular and morphological data have revealed multiple distinct species with different host associations.
weevilbiological-controlthistleinvasive-species-managementCeutorhynchinaerosette-feederCeutorhynchiniBaridinaetaxonomic-revisionclassical-biological-controlCarduusCirsiumOnopordumPalearctic-nativeintroduced-speciesmolecular-systematicsintegrative-taxonomyunivoltineleaf-mineragricultural-pest-controlpasture-weed-managementspecies-complexhost-specificitymusk-thistleplumeless-thistleScotch-thistleIllyrian-thistlewelted-thistleItalian-thistlecrown-weevilrosette-weeviloviposition-behavioroverwinteringegg-stagelarval-stageadult-stagedecaying-organic-mattersoil-surfacenon-photosynthetic-leavesgreen-leavesleaf-midribspetiolesleaf-miningnotching-damagerosette-survivalflowering-stem-reductionseed-production-reductionrosette-mortalitypopulation-density-effectsmark-recapturedispersal-patternsartificial-diet-rearinglaboratory-culturevitamin-supplementationlyophilized-thistle-rootsergosterolcasein-hydrolysate7-dehydrocholesterolsucroselarval-survivaladult-longevityovipositionfemale-fecundityfield-cage-experimentsindividual-cage-experimentsgrowth-parameter-reductionpre-release-host-specificity-testingpost-release-monitoringestablishment-successrange-expansionforested-areasagricultural-landpasturesmall-farmscropsdisturbed-habitatsmeadowsdense-patchesrosette-size-preferencespatial-distributionselective-ovipositionautumn-egg-layingwinter-larval-developmentspring-pupationlate-summer-adult-emergencesoil-overwinteringplant-debris-overwinteringrachisleaf-dissectiondestructive-samplingnon-destructive-samplingsampling-biaslife-stage-detectionestablished-populationsmitochondrial-COInuclear-EF-1αmorphological-charactershost-plant-associationssynonymyspecies-validityintroduction-historyrelease-recordsestablishment-recordsOld-World-nativeNew-World-introductionSouthern-Hemisphere-introductionAustraliaNew-ZealandNorth-AmericaVirginiaSouthwest-VirginiaEuropeSpainFranceGermanyItalySwitzerlandAustriaScandinaviaDenmarkNorwaySwedenColonnelli-1979Panzer-1801Alonso-Zarazaga-&-Sánchez-Ruiz-2002Ceutorhynchinae-vs-Baridinaesubfamily-placementtribe-placementtrue-weevilsCurculionidaeColeopteraInsectaArthropodaAnimalia882-iNaturalist-observationsGBIF-recordsCatalogue-of-Life-acceptedNCBI-TaxonomyBulletin-of-Entomological-ResearchJournal-of-Applied-EcologyJournal-of-Entomological-ScienceAnnals-of-the-Entomological-Society-of-AmericaEnvironmental-EntomologyDOI-10.1017/s000748531500084xDOI-10.1046/j.1365-2664.2002.00747.xDOI-10.18474/0749-8004-22.4.324DOI-10.18474/0749-8004-22.4.330DOI-10.18474/0749-8004-24.4.465DOI-10.1093/aesa/73.6.694DOI-10.1093/ee/10.5.691Trigoniulus corallinus
Rusty Millipede, Common Asian Millipede
Trigoniulus corallinus is a large millipede native to the Indo-Malayan region that has become established as an introduced species across multiple continents. Adults reach 50–75 mm in length and are characterized by a uniform reddish-brown coloration. The species inhabits moist terrestrial environments, particularly areas rich in decaying organic matter. It was the first millipede to have its genome sequenced (2015), and subsequent research has identified an XX/X0 sex chromosome system with males possessing modified seventh-leg pairs (gonopods) used for mating.
Trimium brevicorne
Trimium brevicorne is a small rove beetle in the subfamily Pselaphinae, commonly known as ant-loving beetles. The species occurs across Europe, Northern Asia (excluding China), and has been introduced to North America. It belongs to a group of beetles that are typically found in association with ant colonies.
Trochoideus desjardinsi
handsome fungus beetle
Trochoideus desjardinsi is a species of handsome fungus beetle in the family Endomychidae, characterized by its broad distribution across tropical and subtropical regions. The species exhibits a notable ecological association with social insects, having been documented in nests of ants and termites. Adults are attracted to light and have been collected from various decaying plant materials and economically important crops.
Trogulidae
Trogulid Harvestmen
Trogulidae is a family of harvestmen (order Opiliones) comprising approximately 65 extant species across five genera: Anarthrotarsus, Anelasmocephalus, Calathocratus, Kofiniotis, and Trogulus. Members are characterized by short legs, flattened leathery bodies, and a distinctive habit of adhering soil particles to their bodies for camouflage. The family is primarily distributed in western and southern Europe, extending to western North Africa, the Levant, the Caucasus, and northern Iran. One species, Trogulus tricarinatus, has been introduced to eastern North America. The family includes the only Trogulidae species in Ireland, Anelasmocephalus cambridgei, which has a specialized life history involving egg-laying in empty snail shells.
Tropidosteptes
ash plant bugs
Tropidosteptes is a genus of plant bugs (Miridae) containing at least 30 described species. The genus is best known from T. chapingoensis, the ash plant bug, which has been studied in detail for its life cycle and impact on urban ash trees. Species in this genus are associated with Fraxinus (ash) trees and can cause significant defoliation damage. The genus occurs in North America, with at least one species introduced to South America.
Tropiphorus terricola
Tropiphorus terricola is a broad-nosed weevil in the family Curculionidae. Native to northern Europe, it has been introduced to North America where it has been recorded in eastern Canada and the northeastern United States. The species belongs to the subfamily Entiminae, a group characterized by their broad rostrums and root-feeding larvae.
Tupiocoris rhododendri
Tupiocoris rhododendri is a plant-feeding mirid bug native to North America and introduced to parts of Europe. It is strongly associated with rhododendron plants, on which it feeds exclusively. The species is readily identified by its contrasting coloration of black pronotum, brown wings, and yellow legs. It has been documented in the eastern United States and several European countries including Belgium, Germany, the Netherlands, and the United Kingdom.
Tychius
leguminous seed weevils
Tychius is a large genus of weevils (Curculionidae: Curculioninae: Tychiini) containing over 630 described species. The genus is distributed across the Palearctic (approximately 240 species), Afrotropical (45 species, mainly South Africa), Nearctic, and Oriental regions. All species with documented biology are associated with legume host plants in the subfamily Papilionoideae (Fabaceae), particularly tribes Genisteae, Loteae, Galegeae, Trifolieae, and Vicieae. Several species have been introduced from Europe to North America, where they feed on introduced and native legumes.
Tychius meliloti
Sweet Clover Weevil
Tychius meliloti is a small weevil in the tribe Tychiini, native to Europe and introduced to North America. In Canada, it has been recorded from scattered localities in Saskatchewan, Manitoba, Ontario, and Quebec. The species is associated with sweet clover (Melilotus spp.) as host plants. It represents one of four European Tychius species established in North America.
Tychius picirostris
Clover Seed Weevil
Tychius picirostris is a small weevil in the family Curculionidae, native to Europe and introduced to North America where it has become widespread. The species is commonly known as the Clover Seed Weevil due to its association with clover plants (Trifolium spp.). It was first described by Fabricius in 1787 and has since been recorded across the Palaearctic region, including more recent documentation in China. As a seed-feeding specialist, it represents one of several Tychius species that have established outside their native range through human-mediated dispersal.
Tychius stephensi
red clover seed weevil
Tychius stephensi is a small weevil in the family Curculionidae, commonly known as the red clover seed weevil. The species is native to Europe and has been introduced to North America, where it is now widespread. It is associated with leguminous host plants, particularly species of Trifolium (clover). As a seed weevil, it develops within the seeds of its host plants.
Umbonia crassicornis
Thorn bug, Thorn Treehopper
Umbonia crassicornis is a treehopper species in the family Membracidae, notable for its pronounced sexual dimorphism in pronotal horn structure and extensive maternal care. Adult females deposit approximately 100 eggs into plant stems or under bark, then remain with the developing nymphs until adulthood—a rare subsocial behavior among insects. Nymphs and adults form dense aggregations, with offspring communicating danger to the mother through synchronized vibrational signals that trigger her antipredator defense. The species feeds on plant sap and is occasionally a pest of ornamental and fruit trees in southern Florida and Puerto Rico.
Uroleucon erigeronense
Large fleabane daisy aphid
Uroleucon erigeronense is a species of aphid in the family Aphididae, first described by Thomas in 1878. It feeds primarily on plants in the Asteraceae family, with a particular association with Erigeron (fleabane) species. The species exhibits flexible reproductive strategies: holocyclic in northern climates, producing sexual forms in autumn, and anholocyclic in warmer regions. It shows seasonal host-shifting behavior, moving between overwintering perennial hosts and blooming annuals. Native to North America, it has been introduced to Europe, Australia, and Korea.
Urophora jaceana
Urophora jaceana is a tephritid fruit fly that develops as a gall-former on knapweeds (Centaurea species). The species is native to Europe and has been introduced to eastern Canada. Its larvae induce galls in the flower heads of host plants, primarily black knapweed (Centaurea nigra) and Centaurea debeauxii.
Urozelotes rusticus
Urozelotes rusticus is a cosmopolitan ground-dwelling spider in the family Gnaphosidae and the type species of the genus Urozelotes. Originally described from Europe in 1872, it has been introduced to the Americas, tropical Africa, Australia, and South Africa through human activity. Its synanthropic habits enable it to thrive in buildings and modified environments worldwide.
Velarifictorus
Velarifictorus is a genus of crickets in the family Gryllidae, tribe Gryllini. Species occur naturally across Australia, Asia, and Africa, with at least one species introduced to eastern North America. The genus includes both wing-dimorphic species exhibiting trade-offs between flight capability and reproduction, and species with discrete life cycle modes adapted to different climatic conditions.
Venezillo parvus
Little Pill Woodlouse
Venezillo parvus is a small terrestrial isopod commonly known as the Little Pill Woodlouse. It belongs to the family Armadillidae, a group characterized by their ability to conglobate (roll into a complete ball). The species has been documented in both North America and Europe, with its native range presumed to be European and North American populations representing introduced populations. It is a detritivore that contributes to decomposition processes in terrestrial ecosystems.
Vespa crabro
European hornet
The European hornet (Vespa crabro) is the largest true hornet native to Europe and the only established Vespa species in North America. Introduced to the eastern United States in the mid-1800s, it has spread west to the Rocky Mountains. This eusocial wasp constructs paper nests in enclosed cavities such as hollow trees, wall voids, and abandoned beehives. Unlike many social wasps, it exhibits nocturnal foraging behavior and is attracted to light. While capable of delivering painful stings when nests are disturbed, it is generally less aggressive toward humans than yellowjackets and is not considered a major threat to honey bee colonies.
Wyeomyia mitchellii
bromeliad mosquito
Wyeomyia mitchellii is a mosquito species in the family Culicidae, commonly known as the bromeliad mosquito. Native to the New World, it has been introduced to South Africa, marking the first confirmed record of this species in the Old World. The species is associated with bromeliad phytotelmata (water-holding plants) and has been detected in urban and peri-urban environments through routine vector surveillance.
Xanthochilus saturnius
Mediterranean seed bug
Xanthochilus saturnius, commonly known as the Mediterranean seed bug, is a small true bug in the family Rhyparochromidae. It measures 6–8 mm and displays distinctive black-on-tan coloration. The species is native to southern Europe and the Mediterranean region, with established populations in North America. It feeds primarily on seeds of Lamiaceae and Scrophulariaceae plants.
Xylocopa appendiculata
Appendiculate Carpenter Bee, Asian Carpenter Bee
Xylocopa appendiculata is a large carpenter bee native to eastern Asia, first reported in the United States in 2013 with established populations in northern California. It belongs to the subgenus Alloxylocopa. The species has been studied using distribution modeling to predict its potential spread across North America. Like other carpenter bees, it nests in wood and serves as a pollinator, though specific ecological details for this species remain limited.
Xylocopa sonorina
Valley Carpenter Bee, Hawaiian Carpenter Bee
Xylocopa sonorina is one of the largest bees in California and Hawaii, reaching approximately 25 mm in length. The species exhibits strong sexual dimorphism: females are entirely black, while males are golden-brown with distinctive green eyes. Native to the southwestern United States and adjacent Mexico, it has been introduced to the Hawaiian Islands (since before 1874), French Polynesia, the Samoan Islands, and other Pacific archipelagoes through human-mediated transport of nesting wood. DNA analysis confirmed in 2020 that X. varipuncta is a synonym of X. sonorina. The species is a significant pollinator, including commercial pollination of passion fruit in Hawaii, though its wood-nesting behavior can cause structural damage.
Xysticus cristatus
common crab spider
Xysticus cristatus, commonly known as the common crab spider, is a small ambush predator in the family Thomisidae. Females reach 6–8 mm body length, while males are smaller at 3–5 mm. The species exhibits cryptic coloration ranging from light cream to dark brown or greyish, with distinct patterning that blends with dried leaf litter. It hunts by waiting motionless with forelegs spread wide, capturing insects that blunder within reach. The species has a broad Palearctic distribution and has been introduced to North America.
Yponomeuta malinellus
Apple Ermine, apple ermine moth
Yponomeuta malinellus, the apple ermine moth, is a small ermine moth native to Europe and Asia that has become established in North America. It is a specialist pest of Malus (apple) species, with larvae that feed gregariously within silken tents and can cause significant defoliation. The species has been extensively studied as a target for classical biological control, with multiple parasitoid species introduced to manage outbreaks.
Zelotes tenuis
Zelotes tenuis is a ground spider in the family Gnaphosidae, originally described from the Mediterranean region. The species has a broad native range extending from the Mediterranean basin through Central Europe to the Caucasus region of Russia. It has been introduced to the Galapagos Islands and the United States, with established populations documented on several islands in the Azores (Flores, Pico, Santa Maria, and Terceira). As a member of Zelotes, it belongs to a large genus of nocturnal ground-dwelling spiders.
Zodarion rubidum
European Ant-eating Spider
Zodarion rubidum is a small ant-eating spider native to southwestern France that has expanded its range across central Europe and been introduced to North America. It is a specialized myrmecophagous predator that employs aggressive mimicry to resemble red ants, enabling it to hunt among ant colonies. The species is primarily nocturnal and constructs distinctive igloo-shaped stone retreats for daytime shelter.
Zoropsis spinimana
Mediterranean Spiny False Wolf Spider, Nosferatu-Spinne
Zoropsis spinimana is a medium-sized zoropsid spider native to the Mediterranean region that has expanded its range northward into Central and Northern Europe and been introduced to the United States and United Kingdom. The species is notable for its wolf spider-like appearance but with eyes more spread out along the cephalothorax, and for its strong association with human dwellings where it finds mild temperatures and abundant prey. It is an active nocturnal hunter that does not build webs. Sexual maturity occurs in autumn, with egg-laying in spring. Climate change and human-mediated transport have facilitated its range expansion.
Zygiella
Missing-sector Orbweb Spiders
Zygiella is a genus of orb-weaver spiders distinguished by their distinctive webs, which feature a missing sector containing a single signaling thread that leads to a tubular retreat. First described by F. O. Pickard-Cambridge in 1902, the genus underwent taxonomic revision in 2015 when Parazygiella was synonymized with Zygiella. The genus has a global distribution, with species found across Europe, North America, Asia, and introduced populations in South America and elsewhere.
Zygiella atrica
Zygiella atrica is an orb-weaving spider in the family Araneidae, closely related to the well-known Z. x-notata. It builds a distinctive orb web with two missing sectors and a signaling thread leading to a peripheral retreat. The species is more brown in coloration than Z. x-notata and occupies natural habitats away from human structures. It has been introduced to North America from Europe.
Zygiella x-notata
missing sector orb weaver, silver-sided sector spider, Winter Spider, Opensector Orbweaver
Zygiella x-notata is an orb-weaving spider distinguished by its characteristic web with a missing sector in the upper half, connected by a signal thread to a peripheral retreat. Adult females measure 5–11 mm, males up to 7 mm. The species exhibits strong synanthropic behavior, commonly found on human structures such as window frames, walls, and fences. It has an annual life cycle with reproduction in summer and egg sac production in autumn. Native to Europe, it has been introduced to North America, New Zealand, and other regions worldwide.
Zygogramma suturalis
ragweed leaf beetle
Zygogramma suturalis is a leaf beetle in the family Chrysomelidae, commonly known as the ragweed leaf beetle. Native to North America, it has been introduced to Russia (1978) and other parts of Europe and Asia as a biological control agent for common ragweed (Ambrosia artemisiifolia). The beetle exhibits strong host specificity, feeding almost exclusively on this plant. Despite establishment in introduced ranges, it has achieved only moderate biological success due to low population densities and limited impact on host plant populations.