Aquatic
Guides
Poduridae
Water Springtails
Poduridae is a small family of springtails (Collembola) containing a single genus, Podura. Members are stout-bodied and commonly known as water springtails due to their association with aquatic or semi-aquatic habitats. The family constitutes the monotypic superfamily Poduroidea and includes four described species. These springtails are part of the order Poduromorpha, one of the three major lineages of Collembola.
Poecilocera
Poecilocera is a monotypic genus of aquatic leaf beetles in the family Chrysomelidae, containing the single species Poecilocera harrisii. The genus was established by Schaeffer in 1919. The name has been used historically in both Coleoptera and Orthoptera, creating taxonomic confusion.
Psephenus herricki
Herrick's Water Penny Beetle
Psephenus herricki is a water penny beetle found in eastern North America. Larvae are highly flattened and inhabit stream riffles, where they occupy interstitial crevices and undersides of stones. The species exhibits specific behavioral and morphological adaptations to flowing water environments, including thigmokinesis that inhibits movement when wedged in substrate. Adults are associated with wave-splashed rocks that serve as mating sites and oviposition substrates.
Pseudochironomus
nonbiting midge
Pseudochironomus is a genus of nonbiting midges in the family Chironomidae, containing more than 20 described species distributed across the Americas and Europe. The genus belongs to the tribe Pseudochironomini within subfamily Chironominae. Larvae are aquatic and have been studied for their growth responses to diet quality and thermal conditions.
Ranatra
water stick-insect, water scorpion, water mantis
Ranatra is a genus of slender aquatic predatory insects in the family Nepidae, commonly called water stick-insects or water scorpions. The genus contains over 140 species distributed across freshwater habitats worldwide, with highest diversity in South America and Asia. These insects are sit-and-wait predators that use raptorial forelegs to capture prey. They possess a distinctive long caudal siphon for breathing while submerged.
Ranatra drakei
Ranatra drakei is a species of water scorpion in the family Nepidae, described by Hungerford in 1922. Like other members of the genus Ranatra, it is an aquatic predatory insect with raptorial forelegs adapted for capturing prey. The species is known from North America, though specific ecological details remain poorly documented in published literature.
Ranatra fusca
brown water scorpion, brown waterscorpion
Ranatra fusca is a predatory aquatic bug in the family Nepidae, commonly called the brown water scorpion. Native to North America, it inhabits freshwater environments where it hunts small invertebrates using raptorial forelegs. Adults reach 3.2–4.2 cm in length and possess a long respiratory siphon for breathing at the water surface. The species is most active from spring through autumn.
Ranatra montezuma
Montezuma waterscorpion
Ranatra montezuma is a waterscorpion species endemic to Montezuma Well, a thermally constant, fishless spring in Yavapai County, Arizona. It was described by J. Polhemus in 1976 and represents a highly localized population with specific dietary adaptations to its unique aquatic environment. The species exhibits nocturnal foraging behavior and maintains high population densities supported by abundant endemic prey.
Ranatra quadridentata
waterscorpion
Ranatra quadridentata is a species of waterscorpion described by Stål in 1862. As a member of the family Nepidae, it is an aquatic predatory insect that inhabits freshwater environments. The species has been documented in Central America and North America, with 188 observations recorded on iNaturalist.
Rhagovelia obesa
riffle bug
Rhagovelia obesa is a small aquatic true bug in the family Veliidae, commonly known as a riffle bug or smaller water strider. It inhabits flowing water environments where it uses a unique swimming plume to move underwater. The species has an unusual life history among aquatic Hemiptera, with four nymphal instars rather than five and eggs as the overwintering stage. It has been successfully reared in laboratory conditions from first instar to adult.
Rhantus
Rhantus is a genus of predaceous diving beetles (Dytiscidae) comprising approximately 100 species with worldwide distribution. Members of this genus are primarily associated with lentic freshwater habitats, particularly pools and marshy wetlands. The genus is currently recognized as paraphyletic; taxonomic revision is anticipated following 2017 research that transferred 17 species to newly established genera (Nartus, Meridiorhantus, Caperhantus, and Carabdytes). Several species have independently colonized oceanic islands and undergone endemic diversification.
Rhantus wallisi
Rhantus wallisi is a predaceous diving beetle in the family Dytiscidae, described by Hatch in 1953. The species is endemic to North America, with documented occurrences in western Canada including Alberta and British Columbia. Like other members of the genus Rhantus, it is an aquatic predator inhabiting freshwater environments.
Rhizelmis
Rhizelmis is a genus of riffle beetles (family Elmidae) established by Chandler in 1954. These beetles are aquatic insects inhabiting running water environments. The genus is part of the tribe Elmini within the subfamily Elminae.
Sanfilippodytes pacificus
Sanfilippodytes pacificus is a predaceous diving beetle in the family Dytiscidae. The species was described by Fall in 1923 and is known from western North America, including Alaska and British Columbia. Like other members of Dytiscidae, it is an aquatic predator.
Sepedon americana
American snail-killing fly
Sepedon americana is a species of marsh fly in the family Sciomyzidae, commonly known as snail-killing flies. The species was described by Steyskal in 1951. Like all members of the genus Sepedon, its larvae are obligate predators of aquatic pulmonate snails. The species occurs in North America and has been documented in regions including Colorado. Adults are active early in the year, with observations in February recorded.
Sepedon armipes
marsh fly
Sepedon armipes is a North American species of marsh fly in the family Sciomyzidae, commonly known as snail-killing flies. Like other members of its genus, its larvae are aquatic predators of pulmonate snails. The species exhibits early-season activity, with adults observed active as early as February.
Sepedon floridensis
Florida snail-killing fly
A species of snail-killing marsh fly in the family Sciomyzidae, endemic to Florida. Adults are active in early spring and are associated with aquatic habitats where their predatory larvae feed on pulmonate snails. The species was described by Steyskal in 1951 and belongs to a genus with 20 recognized species in North America, many of which have been investigated for potential biological control of snail vectors of parasitic diseases.
Sepedon fuscipennis
marsh fly
Sepedon fuscipennis is a species of marsh fly in the family Sciomyzidae. The larvae are aquatic predators of pulmonate snails, living just beneath the water surface suspended by water-resistant hairs surrounding their posterior spiracles. Adults are slender flies with a concave face and jutting antennae; males have distinctive bowed hind tibiae and swollen, toothed hind femora for grasping females during mating. The species exhibits overlapping generations during summer with unimodal population peaks, and has been studied for its potential in biological control of snail hosts of parasitic diseases.
Sialis rotunda
Alderfly
Sialis rotunda is a species of alderfly in the family Sialidae, order Megaloptera. It is a small to medium-sized aquatic insect whose larvae develop in freshwater habitats. Adults are short-lived and primarily focus on reproduction. The species was described by Nathan Banks in 1920 and is native to western North America.
Sigara
water boatmen
Sigara is a genus of water boatmen (family Corixidae) comprising approximately 100 species of aquatic true bugs. The genus is notable for containing halophilic species capable of inhabiting saline and hypersaline waters, including extreme environments such as the Makgadikgadi Pans in Botswana. Members of this genus are aquatic insects found in various freshwater and saline habitats across multiple continents.
Sigara trilineata
Sigara trilineata is a species of water boatman in the family Corixidae, found in North America. Water boatmen are aquatic insects that inhabit freshwater environments. The species name "trilineata" refers to three lines, likely describing a distinctive marking pattern on the body. As a member of the Corixidae, it possesses the family's characteristic oar-like hind legs adapted for swimming.
Sisyra
spongillafly, spongilla-fly
Sisyra is a genus of spongillaflies (Neuroptera: Sisyridae), a small family of aquatic insects. The genus comprises at least eight described species distributed across multiple continents, including Brazil, Panama, Australia, and Asia. Sisyra species have been documented in freshwater habitats, with larvae associated with freshwater sponges. The family holds a basal phylogenetic position within Neuroptera, and at least one species (S. nigra) exhibits an unusual achiasmatic sex chromosome segregation mechanism not observed in other neuropterans.
Sperchonopsis
Sperchonopsis is a genus of water mites in the family Sperchontidae. The genus was established by Piersig in 1896 and contains species found in Europe and North America. Sperchonopsis phreaticus is the only formally described species currently associated with this genus. These mites belong to the diverse group of prostigmatic mites within the order Trombidiformes.
Sperchopsis tessellata
Checkered Water Beetle
Sperchopsis tessellata, commonly known as the Checkered Water Beetle, is a species of water scavenger beetle in the family Hydrophilidae. It is distributed across eastern North America, from Canada through the eastern and central United States. As a member of the Hydrophilidae family, it is adapted to aquatic environments. The species was first described by Ziegler in 1844 under the basionym Spercheus tessellatus.
Sphaerius
Sphaerius is a genus of minute beetles in the family Sphaeriusidae, comprising 18 extant species. These beetles are among the smallest in Coleoptera, measuring 0.5–1.2 mm in length. They inhabit damp environments near water bodies across all continents except Antarctica. The genus has undergone significant taxonomic revision, with its family name changing from Sphaeriidae to Microsporidae and finally to Sphaeriusidae.
Stenelmis
riffle beetle
Stenelmis is the largest and most widespread genus of beetles in the family Elmidae. Members are commonly known as riffle beetles due to their association with fast-flowing stream habitats. The genus contains numerous species distributed across multiple continents, with documented presence in North America, Europe, and the Caucasus region.
Stenelmis bicarinata
riffle beetle
Stenelmis bicarinata is a species of riffle beetle in the family Elmidae, first described by LeConte in 1852. Riffle beetles are aquatic insects associated with running water habitats. The species occurs in Central and North America, though detailed ecological studies remain limited.
Stenocolus
Stenocolus is a monotypic genus of beetles in the family Eulichadidae. The sole described species, S. scutellaris, is a forest stream beetle found in western North America. The genus belongs to a small family of aquatic or semi-aquatic beetles associated with running water habitats.
Stygoparnus
Comal Springs dryopid beetle (for sole species S. comalensis)
Stygoparnus is a monotypic genus of dryopid beetles containing the single species Stygoparnus comalensis, known as the Comal Springs dryopid beetle. The genus is endemic to central Texas spring systems fed by the Edwards Aquifer. Its sole member is a federally endangered, subterranean-obligate aquatic beetle with vestigial eyes and reduced pigmentation. The genus represents the only known aquatic lineage within the family Dryopidae.
Stygoparnus comalensis
Comal Springs dryopid beetle
Stygoparnus comalensis is a federally endangered, subterranean-obligate dryopid beetle endemic to three spring systems in the Edwards Aquifer region of central Texas. Adults are approximately 2 mm long with vestigial eyes and undeveloped wings, reflecting their troglobitic ancestry. The species exhibits extreme population genetic structure with no gene flow among localities, indicating evolutionary isolation. Captive studies reveal strong habitat preferences for wood substrates and specific phototactic responses to light wavelength. The beetle serves as a surrogate species for monitoring aquifer health and faces threats from groundwater extraction, pollution, and drought-induced springflow reduction.
Suphis
Suphis is a genus of small aquatic beetles in the family Noteridae, first described by Aubé in 1836. The genus contains approximately eleven described species distributed primarily in the Americas, with records from North, Central, and South America. Members of this genus are associated with freshwater habitats, particularly wetlands and slow-moving waters. As part of the Noteridae family, they represent one of several genera within the diverse group of predaceous diving beetles.
Suphisellus puncticollis
Suphisellus puncticollis is a burrowing water beetle described by Crotch in 1873. It belongs to the subfamily Noterinae within the family Noteridae, a group of small aquatic beetles adapted to living in muddy substrates. The species has been recorded in Canada (Ontario, Québec) and the United States.
Synaptonecta issa
Synaptonecta issa is a minute water bug species in the family Micronectidae, first described by Distant in 1910. The species belongs to a genus of tiny aquatic true bugs that inhabit freshwater environments. Limited observational data exists, with only six iNaturalist records documented. The species has a disjunct distribution spanning North America and Southern Asia.
Tabanus atratus
Black Horse Fly
Tabanus atratus, commonly known as the black horse fly, is a large, all-black species of horse fly in the family Tabanidae. It is one of the largest horse flies in North America, with body lengths ranging from 20–25 mm. Females are blood-feeders with scissor-like mouthparts used to cut skin and lap blood, while males have reduced mouthparts and do not feed on blood. The species is recognizable by its uniform black coloration and distinctively hooked antennae. Females lay eggs in large masses of 100–1000 eggs near water's edge, with each female capable of producing three to four egg masses.
Tanysphyrus lemnae
Duckweed Weevil
Tanysphyrus lemnae is a small weevil species native to Europe with established populations in North America. The larvae are leaf-miners that develop within duckweed plants of the genus Lemna. The species is commonly known as the Duckweed Weevil due to this specialized host relationship.
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
Stretch Spiders, Long-jawed Orb Weavers
Tetragnatha is a large genus of long-jawed orb-weaving spiders with hundreds of species distributed worldwide, though most occur in tropical and subtropical regions. These spiders are characterized by their elongated bodies, extremely long legs, and notably elongated chelicerae (jaws) with well-developed teeth. They construct horizontal orb webs, often near water, and many species can run across water surfaces. The genus exhibits remarkable variation in dispersal ability, with some species being excellent dispersers capable of colonizing islands, while others appear to have secondarily lost this capacity. Hawaiian Tetragnatha species have undergone adaptive radiation, with some lineages evolving cursorial (running) behavior and abandoning web-building entirely.
spiderorb-weaverlong-jawedaquaticstretch-spideradaptive-radiationHawaiicursorial-evolutionhorizontal-webwater-walkingcamouflagemultivoltinesocial-spiderTetragnathidaeAraneaeArachnidapredatorinsectivoreriparianwetlandmeadowtropicalsubtropicalcosmopolitandispersalisland-colonizationphylogeographychemical-species-recognitioncommunal-webbingkleptoparasitism-targetThermonectus nigrofasciatus nigrofasciatus
Thermonectus nigrofasciatus nigrofasciatus is a subspecies of predatory diving beetle in the family Dytiscidae. The nominate subspecies occurs in North and Middle America. Members of the genus Thermonectus are recognized for their distinctive color patterns and aquatic lifestyle.
Tipula abdominalis
giant crane fly
Tipula abdominalis, commonly known as the giant crane fly, is a large species of crane fly in the family Tipulidae. The larvae are aquatic detritivores found in riparian habitats, where they feed on decomposing leaf litter. Their hindgut harbors a dense, diverse bacterial community that facilitates digestion of lignocellulosic material. The species has been studied for its potential applications in biofuel production due to its efficient natural biorefinery system. Adults are among the largest crane flies in North America but do not feed.
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.
Xylotopus par
Xylotopus par is an aquatic xylophagous midge in the family Chironomidae. The larvae colonize submerged wood substrates in freshwater streams, feeding on decaying wood. Populations exhibit plastic phenology, with development rates varying based on wood substrate quality—larvae in fresh, introduced wood can complete development in a single summer, while those in indigenous logs normally require a full year. The species has been studied for its unique bacterial associations in the larval midgut, where morphotypically uniform bacteria form a well-defined band in the posterior midgut's ectoperitrophic space.
Zapada frigida
Frigid Forestfly
Zapada frigida is a species of spring stonefly in the family Nemouridae, commonly known as the Frigid Forestfly. Like other members of the genus Zapada, adults retain diagnostic branched cervical gills from the nymphal stage, with two sets of branched gills on each side of the body. The species has been documented from western North America including Alberta, Alaska, British Columbia, California, and Colorado.