Winter-active
Guides
Agabus ambiguus
Agabus ambiguus is a predaceous diving beetle in the family Dytiscidae, belonging to the North American endemic ambiguus species group. Adults are active in open water year-round, including throughout winter. The species occurs across the United States and Canada, where it inhabits depositional areas of springs, streams, and stream-fed ponds.
Anthracopteryx
Anthracopteryx is a monobasic genus of click beetles (family Elateridae) endemic to the Front Ranges of Colorado, USA. The genus contains a single species, A. hiemalis, which is notable for its winter activity period—unusual among click beetles. The genus was established by Horn in 1891 and remains poorly represented in collections and online databases.
Anthracopteryx hiemalis
Anthracopteryx hiemalis is a small click beetle (family Elateridae) and the sole species in its monotypic genus. It is notable for winter activity, a rare trait among click beetles. The species has an extremely restricted endemic range in the Front Range of Colorado, USA, spanning from Laramie south to Westcliffe. As of 2017, it was documented in only two observations on iNaturalist and had no prior photographic records on BugGuide.net, indicating it is among the most poorly documented North American elaterids.
Arpedium
Arpedium is a Holarctic genus of rove beetles (Staphylinidae: Omaliinae: Anthophagini) first described by Erichson in 1839. The genus comprises approximately 14 species distributed across the Nearctic and Palaearctic regions, including Europe, Japan, North America, and Central Asia. At least one species, A. cribratum, has been identified as a subnivium specialist—active beneath winter snowpack and rare or inactive during summer. The genus has undergone taxonomic revision, with five new species described recently and several synonymies resolved.
Arpedium cribratum
Arpedium cribratum is a small rove beetle (Staphylinidae: Omaliinae) in the Quadrum species group. It is one of four arthropods identified as a possible subnivium specialist—organisms that have evolved to live in the air gap beneath winter snowpack and appear rare or inactive during summer. The species is transcontinental and boreal in distribution, occurring across northern North America.
Boreus brumalis
mid-winter boreus, snow scorpionfly
Boreus brumalis, commonly known as the mid-winter boreus or snow scorpionfly, is a small, wingless insect in the family Boreidae. Despite its common name, it is neither a scorpion nor a fly, but belongs to the order Mecoptera. Adults are active during winter months and can be observed running across snow and ice. This species is found in North America, including the northeastern United States. Males possess distinctive upward-curving genitalia that resemble a scorpion's stinger, though the insect cannot sting. Snow scorpionflies are believed to be ancient relatives of fleas.
Boreus californicus
California Snow Scorpionfly
Boreus californicus is a flightless species of snow scorpionfly endemic to western North America. It is active on snow surfaces across a broad elevation gradient from valley grasslands to alpine areas above tree line. The species exhibits a distinctive life history tied to snow cover, with mating occurring directly on snow surfaces. Surface activity has been documented at temperatures ranging from −5.0°C to 5.5°C, with pairs in copula observed between −0.5°C and 5.5°C.
Boreus coloradensis
snow scorpionfly
Boreus coloradensis is a species of snow scorpionfly in the family Boreidae, described by Byers in 1955. Despite their common name, these insects are neither scorpions nor true flies. Adults are active during winter months and have been observed on snow, ice, and moss. They belong to one of the smallest insect orders, Mecoptera, and are believed to be ancient relatives of fleas.
Boreus insulanus
Island Snow Scorpionfly
Boreus insulanus is a species of snow scorpionfly endemic to Vancouver Island, British Columbia. It belongs to the family Boreidae, a group of small, cold-adapted insects active during winter months. Like other snow scorpionflies, it lacks functional wings and is among the rarest insects encountered in its region. The species was described by Blades in 2002.
Boreus nivoriundus
snow-born boreus, snow scorpionfly
Boreus nivoriundus is a wingless snow scorpionfly in the family Boreidae, active during winter months in boreal and temperate regions of North America. Adults are typically 5 mm or less in length and feed on mosses and liverworts. Males possess prominent upward-curving genitalia that resemble a scorpion's stinger, giving the group its common name. The species exhibits a distinctive mating behavior where males carry females on their backs in a 'nuptial ride.' Despite their common name, snow scorpionflies are neither scorpions nor true flies, but belong to the order Mecoptera, believed to be ancestral relatives of fleas.
Boreus nix
snow scorpionfly
Boreus nix is a species of snow scorpionfly in the family Boreidae, first described by Carpenter in 1935. It belongs to an unusual group of insects adapted to cold environments, with adults active during winter months when most other insects are dormant. The species is documented from North America, though specific details about its biology and ecology remain limited in published literature.
Boreus reductus
Snow scorpionfly
Boreus reductus is a wingless species of snow scorpionfly in the family Boreidae, order Mecoptera. Adults are active during winter months and can be observed hopping across snow and ice. Unlike many Mecoptera, this species lacks functional wings entirely. Adults and larvae feed on mosses and liverworts. Males possess enlarged, upward-curving genitalia that resemble a scorpion's stinger, giving the group its common name. The species engages in a distinctive mating behavior where males carry females on their backs.
Brochymena myops
rough stink bug, tree stink bug
Brochymena myops is a species of rough stink bug native to North America, belonging to the genus Brochymena commonly known as "tree stink bugs" for their bark-like camouflage. The species ranges from Quebec to Florida and westward through the central United States to Texas. Adults are active during warm periods throughout the year, including winter sunny days, and are frequently mistaken for the invasive brown marmorated stink bug. Like other Brochymena species, B. myops is not considered an agricultural or household pest.
stink-bugnativepredatorypine-forestcamouflagewinter-activenon-pestrough-stink-bugtree-stink-bugHemipteraPentatomidaeBrochymenaNorth-Americacentral-United-Statessoutheastern-United-Statesconifer-associatedbark-mimicryoverwintering-adultsingle-generationdecaying-wood-inhabitantbeneficial-insectHalyiniStål-1872Heteropteratrue-bugBycombia
Bycombia is a monotypic genus of moths in the family Drepanidae, subfamily Thyatirinae. It contains a single species, Bycombia verdugoensis, described from southern California in 1927. The genus was established by Benjamin in 1938. Adults are active during winter and early spring.
Calliphora vicina
Blue Blowfly, Blue Bottle Fly
Calliphora vicina is a blow fly in the family Calliphoridae, commonly known as the blue bottle fly due to its metallic blue-gray coloration. It is one of the most important species in forensic entomology because of its predictable colonization patterns on carrion. The species is particularly significant for estimating post-mortem intervals, especially during cooler months when it remains active at temperatures below those tolerated by other blow flies.
Camelopsocus hiemalis
Camelopsocus hiemalis is a small, winter-active barklouse (order Psocodea, family Psocidae) described by Mockford in 1984. It belongs to a monobasic genus, meaning it is the sole species in Camelopsocus. The species is endemic to a restricted area of the Front Ranges in Colorado, USA, where it has been observed active during warm winter days. Its specific epithet 'hiemalis' (Latin for 'of winter') reflects this unusual seasonal activity pattern.
Capniidae
small winter stoneflies, winter stoneflies
Capniidae, the small winter stoneflies, is one of the largest families in the order Plecoptera, comprising approximately 300 species distributed throughout the Holarctic region. Adults are active during winter months, often observed on snow-covered stream banks when most other insects are dormant. The family exhibits notable adaptations to cold environments, including antifreeze compounds and winglessness in some species, which has led to high endemism and restricted distributions. Their closest relatives are the rolled-winged stoneflies (Leuctridae).
Carcinocephalus flavidus
winter rove beetle
Carcinocephalus flavidus, known as the winter rove beetle, is a species of rove beetle in the family Staphylinidae. It is notable for its unusual winter activity period and distinct wing dimorphism between sexes. The species was originally described as Omalium flavidum by Hamilton in 1895. It occurs in northeastern North America, where it has been observed on snow during winter months.
Caurinus
snow scorpionflies
Caurinus is a genus of snow scorpionflies in the family Boreidae, containing two described species: Caurinus dectes from Washington and Oregon, and Caurinus tlagu from Alaska. These tiny, flea-like insects are among the most unusual members of Mecoptera, with a fossil lineage dating back over 145 million years to the Jurassic. They are non-parasitic and feed on leafy liverworts in coastal forest habitats.
Chionea
Snow Flies, Snow Crane Flies
Chionea is a genus of wingless crane flies in the family Limoniidae, commonly known as snow flies. The genus contains approximately 37-40 recognized species distributed across the northern hemisphere, with two subgenera: the Holarctic Chionea and the Palearctic Sphaeconophilus. Adults are uniquely adapted to cold environments and are active during winter months, walking across snow surfaces at sub-zero temperatures. The wingless condition is associated with energy conservation in freezing conditions, with flight muscles replaced by expanded egg storage capacity in females.
Chionea albertensis
snow fly
Chionea albertensis is a wingless crane fly in the family Limoniidae, first described by Charles Paul Alexander in 1941. As a member of the 'snow fly' genus Chionea, it is adapted to cold environments and has been observed active on snow surfaces during winter months. The species is known from western North America, with records from Alberta, British Columbia, and southward to Oregon, Idaho, and Montana. Like other Chionea species, it lacks wings and has modified life history traits associated with subnivean habitats.
Chionea alexandriana
snow fly
Chionea alexandriana is a wingless crane fly species in the family Limoniidae, commonly known as a snow fly. It is active during winter months on snow fields in western North American mountains. Adults are small, measuring 4-8 mm, and are distinguished from related species by specific morphological traits including short antennae and body coloration.
Chionea carolus
Chionea carolus is a wingless crane fly species in the family Limoniidae, commonly known as a "snow fly." It inhabits subnivean environments beneath snow in western North America, particularly in California and Nevada. Adults are active during winter months, crawling on snow surfaces when temperatures are mild enough. The species exhibits remarkable cold tolerance through glycerol-based antifreeze compounds and specialized enzymes that allow metabolic function at low temperatures.
Chionea obtusa
Chionea obtusa is a wingless crane fly in the family Limoniidae, one of sixteen North American species in the genus Chionea commonly known as "snow flies." Described by George Byers in 1983, this species inhabits the Nearctic region of western North America. Like other Chionea species, adults are active during winter months and are adapted to cold environments, though specific biological details for C. obtusa remain largely unstudied.
Chionea scita
snow crane fly, snow fly
Chionea scita is a wingless crane fly native to North America, notable for its winter activity and ability to walk on snow at temperatures as low as 14°F. Adults emerge between September and February, with peak activity in November and December. The species is commonly found in the northeastern United States and Canada, extending south to Georgia and Tennessee. Both sexes are yellow-brown, hairy, and spider-like in appearance, with body lengths of 5–8 mm.
Chionea stoneana
snow fly
Chionea stoneana is a wingless crane fly species in the family Limoniidae, commonly known as a 'snow fly.' Adults are active during winter months and are frequently observed crawling on snow surfaces. The species occurs in the central United States, ranging from Minnesota and Indiana south to Kansas, Oklahoma, and Missouri. Like other members of its genus, it possesses physiological adaptations for cold tolerance, including glycerol in its body fluids that acts as an antifreeze.
Chionea valga
snow fly
Chionea valga is a wingless crane fly commonly known as the snow fly. It is active during winter months, crawling across snow surfaces in cold conditions when most other insects are dormant. Adults are dark-bodied and lack wings entirely, with females storing eggs in the thoracic cavity normally occupied by flight muscles. The species occupies subnivean microhabitats—spaces beneath snow created by vegetation and rodent tunnels—where temperatures remain milder than surface conditions.
Cicurina brevis
Cicurina brevis is a small araneomorph spider species distributed across northern North America. A 2024 study identified this species as a potential subnivium specialist, exhibiting higher population densities beneath seasonal snowpack in winter than during summer months. This seasonal activity pattern suggests adaptation to cold-weather environments, distinguishing it from typical summer-active forest floor spiders.
Coniopteryx
dusty-wings
Coniopteryx is a genus of dusty-wing lacewings in the family Coniopterygidae. Adults are tiny insects covered with a powdery white wax coating produced by specialized abdominal glands. The genus has cosmopolitan distribution and is active during winter months when most other insects are dormant. Larvae are important predators of spider mites, scale insects, and whiteflies.
Criorhina villosa
Winter Bumblefly
Criorhina villosa, commonly known as the winter bumblefly, is a species of hoverfly in the family Syrphidae. It was formerly placed in its own genus, Merapioidus, before being reclassified into Criorhina. The species name has been subject to taxonomic confusion with a related Mexican species originally described as Romaleosyrphus villosus in 1882; as both species now share the genus Criorhina, the older name from 1879 takes precedence.
Culiseta inornata
Winter Marsh Mosquito, Unadorned American Cool Weather Mosquito
Culiseta inornata, commonly known as the winter marsh mosquito, is a species of mosquito in the family Culicidae. It has been extensively studied for its sensory physiology, mating behavior, and osmoregulatory adaptations to brackish water habitats. The species exhibits complex behavioral mechanisms for processing conflicting sensory stimuli and has been documented in central and southern California, where it occurs in marsh and brackish water environments.
Culiseta minnesotae
Minnesota winter mosquito
Culiseta minnesotae is a mosquito species in the family Culicidae, first described by Barr in 1957. The species is known by the common name "Minnesota winter mosquito," suggesting adaptation to cold climates. It belongs to the genus Culiseta, which includes mosquitoes often associated with cool weather activity and overwintering behaviors. Very little specific biological information has been documented for this particular species.
Dermacentor albipictus
winter tick, moose tick
Dermacentor albipictus, commonly known as the winter tick or moose tick, is a one-host hard tick native to North America. It is primarily known as a serious pest of moose (Alces alces), with heavy infestations of up to 150,000 ticks documented on individual animals, often leading to death. The tick also parasitizes other cervids including elk, white-tailed deer, mule deer, and caribou, as well as cattle and horses. Unlike many tick species, D. albipictus is not known to transmit disease pathogens to humans, wildlife, or domestic animals. Its life cycle spans approximately one year, with all feeding stages occurring on a single host.
Desoria hiemalis
Desoria hiemalis is a springtail species in the family Isotomidae, first described by Schött in 1893. It is a winter-active species, as indicated by its specific epithet "hiemalis" (Latin for "of winter"). The species has been recorded from both European and North American localities, including the Pacific Northwest region. It belongs to a diverse genus of soil-dwelling springtails commonly found in cold environments.
Egira hiemalis
Egira hiemalis is a noctuid moth species native to western North America. Adults are active during winter and early spring, an unusual seasonality for Lepidoptera. The species is notable for its cold-weather activity pattern and association with coniferous and hardwood host plants. It was first described by Grote in 1874 under the basionym Xylomiges hiemalis.
Epacalles inflatus
Epacalles inflatus is a species of weevil in the family Curculionidae, described by Kissinger in 1964. The species was formerly classified under the genus Porrhodites as Porrhodites inflatus. Research has identified it as a potential specialist of the subnivium—the air pocket beneath winter snowpack—where it remains active during winter months and is rare or inactive during summer.
Erythroneura tricincta
Three-banded Leafhopper
Erythroneura tricincta, commonly known as the Three-banded Leafhopper, is a small leafhopper species in the family Cicadellidae. It is distinguished by three distinct bands across its wings and is frequently observed on fence lines and building exteriors during mild winter periods. The species is known to overwinter as adults and become active on warm days. Like other Erythroneura species, it feeds on plant sap and can be found in association with various host plants, though specific host relationships for this species are less documented than for congeners such as E. comes.
Eugnosta busckana
Busck's Gallmoth
Eugnosta busckana is a small tortricid moth endemic to California. Adults are active during winter months, with records spanning November through February. The species was originally described as Carolella busckana by Comstock in 1939 and later transferred to Eugnosta. It remains poorly studied, with limited ecological data available beyond basic phenology and distribution.
Graphopsocus cruciatus
F-winged Barklouse
Graphopsocus cruciatus, commonly known as the F-winged Barklouse, is a species of barklouse in the family Stenopsocidae. Native to Europe and parts of Asia, it was introduced to North America around 1930 and has since established populations across the continent. This small insect is notable for its distinctive wing pattern featuring five dark marks on the anterior half and a light "F"-shaped mark on the posterior half. It is frequently observed on building exteriors and vegetation, where it feeds on microflora.
Hadromorphus inflatus
Hadromorphus inflatus is a species of click beetle (Elateridae) native to northeastern North America. The species was previously classified under the genus Porrhodites and has been identified as a potential subnivium specialist—an arthropod adapted to the air pocket beneath winter snowpack. Research suggests it dominates subnivium communities during winter months and is rare or inactive during summer, indicating a specialized cold-season life history.
Hesperoboreus
Hesperoboreus is a genus of snow scorpionflies (Mecoptera: Boreidae) established by Norman Penny in 1977. Members of this genus are small, wingless insects adapted to cold environments. The genus is distinguished from the related Boreus by morphological features of the male genitalia. Very few observations exist, with only three records documented on iNaturalist as of the knowledge cutoff.
Hesperoboreus brevicaudus
Hesperoboreus brevicaudus is a species of scorpionfly in the family Boreidae, commonly known as snow scorpionflies. The species was described by George Byers in 1961 and is one of several western North American species in the genus Hesperoboreus. Like other boreids, adults are active during cold months and are often found on snow. The specific epithet brevicaudus refers to the relatively short abdomen characteristic of this species.
Hydriomena nubilofasciata
oak winter highflier
Hydriomena nubilofasciata, commonly known as the oak winter highflier, is a small geometrid moth that is active during winter months. Adults are associated with oak trees and fly in late January and February. The species is one of the few North American moths with adult activity in mid-winter.
Hymenaphorura cocklei
Golden Snow Flea
Hymenaphorura cocklei is a species of springtail in the family Onychiuridae, commonly known as the Golden Snow Flea. It is an eyeless, soil-dwelling collembolan with a characteristic golden-yellow coloration. The species is primarily recorded from western North America, particularly in forested mountainous regions. It belongs to a genus distinguished by specialized mouthpart structures and reduced pigmentation.
Hypogastrura harveyi
snow flea
Hypogastrura harveyi, commonly known as the snow flea, is a species of springtail in the family Hypogastruridae. It is one of several springtail species referred to as 'snow fleas' due to its habit of appearing on snow during winter months. The species was described by J.W. Folsom in 1902. Springtails in this genus possess a furcula (springing organ) that allows them to escape predators by leaping.
Hypogastrura nivicola
snow flea, dark blue springtail
Hypogastrura nivicola is a small, dark blue springtail commonly known as the snow flea in North America. Despite its common name, it is unrelated to true fleas and belongs to the ancient group Collembola, which predates the first vertebrates on land by millions of years. The species is notable for its ability to remain active on snow surfaces during winter, enabled by glycine-rich antifreeze proteins that prevent ice crystal formation in its tissues. It possesses the characteristic springtail anatomy including a furcula for jumping and a ventral collophore.
Leptinus orientamericanus
Leptinus orientamericanus is a small beetle in the family Leiodidae, described by Peck in 1982. It is one of three North American species in the genus Leptinus, all of which are facultative ectoparasites of small mammals. This species is widespread east of the Mississippi River and has been documented on seven host species, with highest prevalence on Blarina brevicauda (northern short-tailed shrew) and Scalopus aquaticus (eastern mole). Activity is concentrated during fall and winter months.
Leptophlebia
Early brown spinner, Sepia dun, Claret dun
Leptophlebia is a genus of mayflies in the family Leptophlebiidae, comprising approximately 11 described species distributed across the Northern Hemisphere. Nymphs are primarily detritivores that inhabit lentic waters, slow-flowing streams, and floodplain wetlands, with documented movements between river channels and temporary wetland habitats. Several species, including L. vespertina and L. cupida, have been studied as model organisms for understanding life cycle plasticity, acid tolerance, and river-floodplain connectivity in freshwater ecosystems.
Lesteva cribratula
Lesteva cribratula is a small rove beetle (Staphylinidae) native to eastern North America. It has been identified as a likely subnivium specialist, active beneath winter snowpack and rare or inactive during summer months. The species inhabits the air gap between soil and snow, where it likely functions as a predator in cold, stable conditions. Climate change poses a threat to this species through declining snowpack, which exposes subnivium habitats to temperature extremes.
Lesteva pallipes
Lesteva pallipes is a species of rove beetle (Staphylinidae) first described by J.L. LeConte in 1863. Research indicates this species may be a specialist of the subnivium—the air pocket beneath winter snowpack—where it remains active during winter months and is rare or inactive during summer. This apparent seasonal specialization makes it potentially vulnerable to climate change impacts on snowpack persistence.