Holarctic
Guides
Swammerdamia caesiella
Birch Ermel
Swammerdamia caesiella is a small ermine moth in the family Yponomeutidae, commonly known as the Birch Ermel. It has a broad distribution across Europe, Asia, and North America, where it may have been introduced. The species is bivoltine, with adults active in spring and late summer. Larvae specialize on birch foliage.
Symmerus
Symmerus is a Holarctic genus of fungus gnats in the family Ditomyiidae (Diptera). The genus comprises approximately 16 described species distributed across the northern hemisphere, with records from Europe, North America, and Asia. A systematic revision recognized two subgenera: Symmerus s. str. and Psilosymmerus, the latter established with S. coqulus as type species. The genus has been subject to phylogenetic analysis using Hennig's phylogenetic systematics, with transantarctic relationships documented in the related genus Australosymmerus.
Symmerus lautus
Symmerus lautus is a Holarctic species of fungus gnat in the family Ditomyiidae (subfamily Ditomyiinae). The species was originally described as Plesiastina lauta by Loew in 1869 and has been known under the synonyms S. tristis and S. dilutus. The genus Symmerus belongs to a group of non-brachyceran Diptera commonly referred to as fungus gnats, though specific biological details for S. lautus remain poorly documented.
Sympetrum danae
Black Darter, Black Meadowhawk
Sympetrum danae is a small dragonfly with a northern Holarctic distribution, found in northern Europe, Asia, and North America. It is Britain's smallest resident dragonfly at 29–34 mm long. The species is strongly associated with acidic bog habitats and is active from mid-June to mid-November, with peak activity in late summer. Mature males are entirely black, making this the only Sympetrum species lacking red coloration in males.
Sympistis heliophila
Sympistis heliophila is a noctuid moth (owlet moth) with a Holarctic distribution spanning Europe, northern Asia, and North America. The species name 'heliophila' (sun-loving) suggests an association with open, sunny habitats. It belongs to the diverse genus Sympistis, which contains numerous species often difficult to distinguish without detailed examination.
Syneta
Syneta is a genus of leaf beetles comprising approximately 11 described species. It is the sole genus in the subfamily Synetinae, a small lineage within the family Chrysomelidae. The genus has an exclusively Holarctic distribution, occurring in northern regions of North America, Europe, and Asia. The type species, Syneta betulae, was described by Fabricius in 1792.
Synetinae
Synetinae is a small subfamily of leaf beetles (Chrysomelidae) containing two genera, Syneta and Thricolema, with approximately 12 described species. The group is restricted to the Holarctic region, with most species occurring in North America and a smaller number in Europe and Asia. The taxonomic status of Synetinae has been disputed: historically treated as a separate subfamily, it was proposed as tribe Synetini within Eumolpinae based on larval similarities, though this placement remains contested due to conflicting morphological evidence.
Syngrapha diasema
Dwarf Birch Looper
Syngrapha diasema is a noctuid moth distributed across Arctic and subarctic regions of Eurasia and North America. First described by Boisduval in 1829, it is commonly known as the Dwarf Birch Looper. The species has a wingspan of 30–33 mm and completes one generation per year.
Synneuron
Synneuron is a rare genus of flies in the family Canthyloscelidae, with four extant species distributed across the Holarctic region. The genus has an exceptional fossil record extending back to the Lower Cretaceous (ca. 125 Ma), with specimens from Australia and the Eocene of North America, supporting its status as a true Pangean clade that survived major vegetation transitions from gymnosperm to angiosperm dominance. Its ancient origins and relictual modern distribution make it significant for understanding dipteran biogeography and the impact of Cretaceous floral turnover on insect lineages.
Syrphus
Common Flower Flies
Syrphus is a genus of hoverflies in the family Syrphidae, characterized by distinctive calypter morphology. The genus is distinguished from other Syrphini by long hairs on the upper surface of the lower lobe of the calypter, a unique diagnostic feature. Adults are common flower visitors and pollinators, while larvae are primarily aphid predators. The genus includes approximately 20 described species distributed across the Holarctic region, with several species occurring in North America and Europe.
Syrphus ribesii
Common Banded Hoverfly
Syrphus ribesii is a common Holarctic hoverfly and an effective aphid predator in both agricultural and natural ecosystems. Adults are frequent flower visitors, feeding on nectar and pollen while providing pollination services. The species is highly migratory and shows remarkable adaptability to diverse habitats from farmland to forest. Two distinct chromosome races exist across much of Europe.
Syrphus vitripennis
Black-thighed Flower Fly
Syrphus vitripennis is a common Holarctic hoverfly (Syrphidae) with distinctive yellow and black wasp-mimicking coloration. Adults are medium-sized (8–11 mm body length, wing length 7.25–10.25 mm) and frequent flowers from March to October, peaking in July–August. Larvae are aphid predators, making this species economically significant for biological control. The species is highly migratory, with documented seasonal movements between latitudes. It is one of five Syrphus species in Britain and can be difficult to distinguish from congeners, particularly S. rectus in males.
Systenus eucercus
Systenus eucercus is a species of long-legged fly (Dolichopodidae) described by Steyskal in 1970. It belongs to the subfamily Medeterinae, a group characterized by slender bodies and elongated legs. The genus Systenus is distributed across the Holarctic region, with species often associated with moist terrestrial habitats. As with most dolichopodids, adults are predatory and contribute to insect population control in their ecosystems.
Tachinus basalis
Tachinus basalis is a species of rove beetle in the family Staphylinidae, subfamily Tachyporinae. It is a Holarctic species with a broad distribution across northern Eurasia and North America. Like other members of the genus Tachinus, it is likely associated with decaying organic matter and fungal habitats, though specific ecological details remain poorly documented. The species was described by Wilhelm Ferdinand Erichson in 1839.
Tachinusini
Tachinusini is a tribe of rove beetles within the subfamily Tachyporinae. Members are small to medium-sized beetles characterized by compact bodies and relatively short elytra that leave several abdominal segments exposed. The tribe includes the genus Tachinus, which is among the more frequently observed tachyporine groups. Tachinusini species are found primarily in the Northern Hemisphere, with many species adapted to cool, moist microhabitats.
Tachyerges
Tachyerges is a genus of weevils in the family Curculionidae, established by Schoenherr in 1825. The genus comprises at least two recognized species: Tachyerges salicis and Tachyerges stigma. Species in this genus are associated with willow (Salix) host plants. The genus has documented populations across Europe and North America.
Tachyporus abdominalis
Tachyporus abdominalis is a species of rove beetle in the family Staphylinidae, subfamily Tachyporinae. It is a small, active predatory beetle with a Holarctic distribution spanning North America, Europe, and Asia. The species is part of the diverse Tachyporus genus, which contains numerous similar-looking species that are often difficult to distinguish without close examination. Like other members of its genus, it is typically found in moist habitats where it hunts small invertebrates.
Tachyporus maculicollis
Tachyporus maculicollis is a rove beetle (Staphylinidae) described by John Lawrence LeConte in 1866. The species epithet "maculicollis" refers to spotted or marked coloration on the pronotum or neck region. It belongs to the subfamily Tachyporinae, a group characterized by relatively short elytra and flexible abdominal segments. The genus Tachyporus is widely distributed across the Holarctic region, with this species recorded from North America and parts of Eurasia.
Teleiopsis
Teleiopsis is a genus of small moths in the family Gelechiidae, first described by Sattler in 1960. The genus contains eleven recognized species with a predominantly Holarctic distribution centered around the Mediterranean region. Larvae of at least one species (Teleiopsis diffinis) have been documented as leaf-miners, though biological data for most species remains limited.
Temnostoma
Falsehorn Flies
Temnostoma is a genus of hoverflies (Syrphidae) renowned for their sophisticated Batesian mimicry of wasps. Adults possess overall morphological resemblance to hymenopterans, including darkened wing margins that mimic the folded wings of vespid wasps at rest. A distinctive behavioral adaptation involves waving the forelegs in front of the head to simulate wasp antennae. The genus comprises approximately 25 described species distributed across the Holarctic region, with larvae that are saproxylic—developing in wet, decaying wood where they feed on microorganisms.
Tenthredininae
Tenthredininae is a subfamily of sawflies within the family Tenthredinidae, representing one of the most diverse and well-known groups of sawflies. It contains approximately 28-50 genera, including the type genus Tenthredo. Members of this subfamily include most of the larger and more conspicuously colored sawflies in the family. The subfamily is divided into seven recognized tribes, with an eighth tribe (Sioblini) having been elevated to subfamily status as Sioblinae.
Tenthredo
Common Sawflies
Tenthredo is a large genus of sawflies comprising over 700 species with Holarctic distribution. Adults exhibit wasp-mimicry with long antennae and lack the narrow petiole ('wasp waist') characteristic of true wasps. Larvae are herbivorous and feed on diverse host plants, with most species showing host specificity. Adults are predatory or omnivorous, feeding on smaller insects as well as pollen and nectar at flowers. The genus is notable for its complex wing venation and soft-bodied, delicate adults.
Tetanocera ferruginea
common buff snailkiller
Tetanocera ferruginea is a medium to large sciomyzid fly with light brown coloration and no obvious wing markings. It is an obligate malacophage, with larvae preying on non-operculate snails in aquatic and semi-aquatic habitats. The species has a Holarctic distribution and is multivoltine, overwintering in the puparial stage. Despite forming large populations, individuals exhibit very limited movement within habitats.
Tetragnatha extensa
Common Stretch Spider
Tetragnatha extensa is a long-jawed orb-weaver spider with a Holarctic distribution. It is characterized by an extremely elongated body and legs, with females reaching up to 11 mm in body length. The species constructs horizontal orb webs in damp, vegetated habitats and exhibits a distinctive straight-line defensive posture when alarmed. It is the most common species of Tetragnatha in the United Kingdom and among the most frequently encountered long-jawed orb weavers across its range.
Tetrix subulata
Slender Ground-hopper, Slender Groundhopper, Awl-shaped Pygmy Grasshopper, Slender Grouse Locust
Tetrix subulata is a small groundhopper (family Tetrigidae) with a Holarctic distribution spanning the Palearctic and Nearctic regions. The species exhibits striking polymorphism in both coloration and wing development, with long-winged (macropterous) and short-winged (brachypterous) morphs coexisting in populations. It is strongly associated with moist habitats, particularly wet meadows, riverbanks, and mudflats, where it feeds primarily on algae and mosses. The species has been extensively studied for its wing dimorphism, reproductive interference with congeners, and life-history trade-offs between flight capability and reproduction.
Thanatophilus
carrion beetles, silky carrion beetles
Thanatophilus is a genus of approximately 12 described species of carrion beetles in the family Silphidae. These beetles are primarily necrophagous, feeding on decaying animal matter. They occupy the Holarctic and Afrotropical realms and are frequently detected on large carrion, including human remains. Several species are forensically important for estimating time of colonization and post-mortem intervals.
Thanatophilus lapponicus
Northern Carrion Beetle, Silky Carrion Beetle
Thanatophilus lapponicus, the Northern Carrion Beetle, is a holarctic species in the family Silphidae. It is one of the most widespread carrion beetles in the northern hemisphere, occurring across boreal and temperate regions of Europe, Asia, and North America. The species is associated with decomposing animal remains, particularly in cooler climates where its densely hairy body may provide thermal insulation. Adults are active from early spring through autumn and are frequently encountered in forensic entomology contexts.
Thanatophilus trituberculatus
Cold-shore Carrion Beetle
Thanatophilus trituberculatus is a carrion beetle in the family Silphidae. The species occurs across northern regions of both North America and Eurasia. It is associated with cold environments, as indicated by its common name "Cold-shore Carrion Beetle" and its distribution in subarctic and boreal zones. Like other members of its genus, it likely feeds on decomposing animal matter.
Thanatus formicinus
Running Crab Spider, Ant-mimic Crab Spider
Thanatus formicinus is a running crab spider in the family Philodromidae with a Holarctic distribution spanning North America, Europe, and Asia. It is a ground-dwelling hunter active during spring and early summer, often observed basking on warm surfaces like concrete paths. The species exhibits ant-mimicry in both appearance and behavior, a distinctive trait among crab spiders.
Thera
Thera is a genus of moths in the family Geometridae, subfamily Larentiinae, established by Stephens in 1831. The genus comprises numerous species distributed primarily across the Northern Hemisphere. Thera moths are small to medium-sized geometrids with relatively broad wings and cryptic coloration patterns. Larvae typically feed on coniferous trees, making several species economically significant as forest pests.
Theridion pictum
Painted Cobweb Weaver
Theridion pictum is a cobweb spider in the family Theridiidae and the type species of the genus Theridion. It has a Holarctic distribution spanning North America, Europe, and Asia, with introduced populations in South Africa. The species constructs three-dimensional webs in damp, low-lying areas, often on vegetation or man-made structures. Adults mature in early to mid-summer, with females persisting into autumn.
Theridiosoma gemmosum
Common Eastern Ray Spider, Ray Spider
A small Holarctic ray spider distinguished by its unique conical orb web. Females measure 2–3 mm, males 1.5–2 mm. The species constructs a specialized web held under tension by the spider, which is released to snap forward and capture flying prey. Mating involves successive copulations with males providing silk draglines that females ingest as nuptial gifts between copulations.
Thrinax dubitata
Thrinax dubitata is a species of sawfly in the family Tenthredinidae, originally described as Hemitaxonus dubitatus by Norton in 1862. It is one of approximately 40 species in the genus Thrinax, a group of small to medium-sized sawflies primarily distributed in the Holarctic region. The species is recorded from eastern and central Canada, with observations spanning Manitoba to the Atlantic provinces. As with most Tenthredinidae, adults are likely herbivorous or nectar-feeding, though specific ecological details remain poorly documented.
Titanoeca
Titanoeca is a genus of cribellate-web spiders in the family Titanoecidae, established by Thorell in 1870. The genus comprises 31 species as of January 2026, distributed primarily across Eurasia with notable exceptions: three species endemic to North America (T. americana, T. brunnea, T. nigrella), one holarctic species (T. nivalis), and one Ecuadorian endemic (T. guayaquilensis). Members construct cribellate webs and exhibit conditional foraging behavior.
Tomocerus
elongate springtails
Tomocerus is a genus of elongate springtails (Collembola) in the family Tomoceridae, characterized by their relatively large size among springtails and distinctive body proportions. Species in this genus are distributed across multiple continents including Europe, Asia, and the Americas, with some species exhibiting troglomorphic adaptations in cave habitats. The genus has been subject to taxonomic revision, with species complexes such as the kinoshitai and ocreatus groups recognized. Tomocerus vulgaris is a notable species that has been studied for its life history and ecological interactions, including serving as prey for specialized predators such as harvestmen.
Tournotaris bimaculata
Tournotaris bimaculata is a species of weevil in the family Brachyceridae, originally described by Fabricius in 1787 under the name Curculio bimaculatus. The species has a Holarctic distribution, with records indicating presence in parts of Europe. As a member of the Curculionoidea superfamily, it possesses the characteristic elongated snout typical of weevils.
Tragosoma
Tragosoma is a genus of large saproxylic longhorn beetles in the subfamily Prioninae, distributed across the Holarctic region. The genus includes approximately six described species, with Tragosoma depsarium being the most widely studied and the type species. These beetles are obligate deadwood specialists whose larvae develop in the sapwood of conifers, particularly pines. Adults are notable for their robust, somewhat flattened bodies and relatively short antennae compared to other cerambycids. Several species are of conservation concern due to their dependence on specific deadwood microhabitats threatened by modern forestry practices.
Tragosoma harrisii
Hairy Pine Borer
Tragosoma harrisii is a large longhorned beetle in the family Cerambycidae, subfamily Prioninae. It is one of the few North American cerambycids with a Holarctic distribution, also occurring in Europe and Asia. The species is associated with coniferous forests and has been documented in boreal and montane regions across its range. Adults are active during summer months and have been collected using sweet red wine-baited traps.
Trechus apicalis
Trechus apicalis is a species of ground beetle in the subfamily Trechinae, first described by Motschulsky in 1845. It belongs to the large genus Trechus, which comprises numerous small carabid beetles often associated with cool, moist habitats. The species has a Holarctic distribution, occurring across northern regions of North America and Eurasia.
Trechus chalybeus
Trechus chalybeus is a small ground beetle in the family Carabidae, subfamily Trechinae. The species was described by Dejean in 1831 and has been historically placed in the genus Epaphius by some authorities. It is known from North America with records across the northern United States, Canada, and Alaska. As a member of the large genus Trechus, it shares the typical characteristics of small, often metallic carabid beetles associated with ground-level habitats.
Tremex
woodwasp, horntail
Tremex is a genus of woodwasps (family Siricidae) containing approximately 33 species with a primarily Holarctic distribution. These large, cylindrical wasps are characterized by females possessing a prominent, spear-like ovipositor used to bore into hardwood trees and lay eggs. Unlike their relatives in the subfamily Siricinae, Tremex species associate with the white-rot fungus Cerrena unicolor rather than Amylostereum. The larvae tunnel through wood and feed on both the fungus and decayed wood material. Though they appear intimidating due to their size and visible ovipositor, they are non-venomous and pose no threat to humans.
Trichiosoma
Hairy-clubhorn Sawflies
Trichiosoma is a genus of large-bodied sawflies in the family Cimbicidae, comprising more than 30 described species. These insects are commonly known as Hairy-clubhorn Sawflies, reflecting their robust, often hairy appearance. Adults are active during summer months and are associated with woody vegetation. Larvae are solitary herbivores that feed on leaves.
Trichocera
winter crane flies
Trichocera is a genus of winter crane flies comprising over 140 described species. Adults are among the few insects regularly active during winter months, often appearing at porch lights or forming aerial swarms on sunny days. The genus is distinguished from other crane flies by the presence of three ocelli on the crown of the head. Most North American species belong to this genus, with larvae developing in decaying organic matter including leaf litter, compost, fungi, and manure.
Trichoceridae
winter crane flies, winter gnats
Trichoceridae, commonly known as winter crane flies or winter gnats, is a small family of delicate, long-legged flies in the order Diptera. Adults are active primarily during cold seasons, including fall, winter, and early spring, with some species observed in snow. They are distinguished from other crane fly families by the presence of three ocelli (simple eyes) on the crown of the head. The family contains approximately 160 described species worldwide, with most diversity concentrated in non-tropical, Holarctic regions. Larvae inhabit moist terrestrial environments where they feed on decaying organic matter.
Trichoclinocera
Trichoclinocera is a genus of aquatic dance flies in the family Empididae, subfamily Clinocerinae. The genus contains approximately 30 described species distributed across the Holarctic and eastern Asia, with 16 species recognized from the Nearctic region and nine from Japan. Species are organized into six species-groups based on morphological characteristics, primarily of the male terminalia. The genus was established by Collin in 1941 and has undergone significant taxonomic revision, with Seguyella and Acanthoclinocera recently synonymized under Trichoclinocera.
Trichodes
checkered beetles
Trichodes is a genus of checkered beetles (family Cleridae) containing approximately 64 species, with 11 species occurring in North America. The genus includes some of the largest and most strikingly colored members of the family. Adults are frequently found on flowers where they feed on pollen and nectar, while larvae are specialized predators that develop within the nests of bees and wasps.
Trichophyinae
Trichophyinae is a monotypic subfamily of rove beetles (Staphylinidae) containing only the genus Trichophya. Established by Thomson in 1858, this subfamily represents one of the most species-poor lineages within the hyperdiverse rove beetle family. The genus Trichophya contains multiple described species, though the exact number remains uncertain due to taxonomic revisions. These beetles are rarely encountered and poorly represented in collections.
Trigonurinae
Trigonurinae is a monogeneric subfamily of rove beetles (Staphylinidae) containing only the genus Trigonurus. The group has a Holarctic distribution with approximately nine described species. Most species occur in North America (seven species), with two in the western Palaearctic and two in China. The subfamily was established by Reiche in 1866.
Triphosa
Triphosa is a genus of moths in the family Geometridae, subfamily Larentiinae, established by Stephens in 1829. The genus occurs across the Holarctic region, with species documented in Europe, Asia, and North America. Several species, notably Triphosa dubitata and T. sabaudiata, exhibit obligate cave-dwelling behavior as adults, a distinctive ecological trait within the Geometridae. The genus has been subject to recent taxonomic revision in the Western Palaearctic, resulting in synonymies and description of new species.
Trixoscelis signifera
Trixoscelis signifera is a species of fly in the family Heleomyzidae, described by Melander in 1952. It belongs to the subfamily Trixoscelidinae, a group of small to medium-sized flies. The genus Trixoscelis is primarily distributed in the Holarctic region. Like other members of Heleomyzidae, this species is likely associated with decaying organic matter, though specific ecological details remain poorly documented.