Caenis

Superregnum: Eukaryota
Cladus: Unikonta
Cladus: Opisthokonta
Cladus: Holozoa
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Protostomia
Cladus: Ecdysozoa
Cladus: Panarthropoda
Phylum: Arthropoda
Subphylum: Hexapoda
Classis: Insecta
Cladus: Dicondylia
Subclassis: Pterygota
Ordo: Ephemeroptera
Subordo: Furcatergalia
Infraordo: Pannota
Superfamilia: Caenoidea

Familia: Caenidae
Subfamilia: Caeninae
Genus: Caenis
Species: C. amacayacu – C. elidioi – C. gaucha – C. horaria – C. pycnacantha –
References

Jia, Y-y.; Qin, J-z.; Ju, M.; Zhou, C-f. 2010: A new mayfly species of Caenis from headwater of Zijin Hill (Nanjing, Eastern China) (Ephemeroptera: Caenidae). Zootaxa, 2535: 61–68. Preview
Lima, L.R.C. & Boldrini, R. 2017. New distributional records and life stage description of Caenis species (Ephemeroptera: Caenidae) from Brazil. Zootaxa 4276(2): 285–292. DOI: 10.11646/zootaxa.4276.2.10. Reference page.
Lima, L.R.C., Molineri, C. & Pinheiro, U. 2015: A new species of Caenis Stephens, 1836 (Ephemeroptera: Caenidae) from Southern Brazil. Zootaxa 3941(4): 589–592. DOI: 10.11646/zootaxa.3941.4.8. Preview Reference page.
Lima, L.R.C., Molineri, C., Pinheiro, U. & Salles, F.F. 2016. Two new species of Caenis Stephens, 1835 (Ephemeroptera: Caenidae) from South America. Zootaxa 4170(1): 114–124. DOI: 10.11646/zootaxa.4170.1.5. Reference page.
Malzacher, P. 2011: The West African species of Caenis Stephens (Insecta: Ephemeroptera). Stuttgarter Beiträge zur Naturkunde (A) (n.s.), 4: 43–74. PDF

Caenis is a genus of mayflies. They are very small in size, sometimes with a body of only an 1/8 of an inch (3.2 mm).

Distribution and ecology

Caenis is one of the most abundant mayfly genera of the Holarctic. Larvae can occur in high densities on the bottoms of shallow ponds and lakes up to an altitude of 1800 meters in the [Alps].[1]

Densities of 700-1700 larvae per square meter have been reported for C. luctuosa and C. horaria on bottoms covered with organic detritus or decaying leaves. Densities on mineral sediments are an order of magnitude lower (4-330 animals per square meter).[2]
Species

Caenis amica Hagen, 1861
Caenis anceps Traver, 1935
Caenis arwini McCafferty & Davis, 2001
Caenis bajaensis Allen & Murvosh, 1983
Caenis candida Harper & Harper, 1981
Caenis diminuta Walker, 1853
Caenis hilaris (Say, 1839)
Caenis horaria (Linnaeus, 1758)
Caenis latipennis Banks, 1907
Caenis luctuosa (Burmeister, 1839)
Caenis macafferti Provonsha, 1990
Caenis punctata McDunnough, 1931
Caenis tardata McDunnough, 1931
Caenis youngi Roemhild, 1984

Varia

Imitations of this mayfly in hook sizes as small as # 28 are used for fly-fishing.[3] Tying fly imitations this small is difficult, hence the nickname "Anglers Curse."
References

Menetrey, N; B Oertli; M Sartori; A Wagner; JB Lachavanne (2008). "Eutrophication: are mayflies (Ephemeroptera) good bioindicators for ponds?". Hydrobiologia. 597 (1): 125–135. doi:10.1007/s10750-007-9223-x.
Int Panis, L; Bervoets L; Verheyen RF (1995). "The spatial distribution of Caenis horaria (L., 1758)(Caenidae, Ephemeroptera) in a pond in Niel (Belgium)". Bull. Ann. Soc. R. Ent. Belg. 131: 47–51.
Jason Neuswanger. "Mayfly Genus Caenis (Angler's Curses)". Troutnut.com. Retrieved 30 December 2014.