Published May 4, 2024. Open access.

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Triangle Watersnake (Hydrops triangularis)

Reptiles of Ecuador | Serpentes | Colubridae | Hydrops triangularis

English common name: Triangle Watersnake.

Spanish common names: Culebra acuática triangular, culebra de agua triángulo.

Recognition: ♂♂ 75.2 cmMaximum distance from the snout to the tip of the tail. Snout–vent length=60.5 cm. ♀♀ 80.6 cmMaximum distance from the snout to the tip of the tail. Snout–vent length=68 cm..1,2 Hydrops triangularis can be identified by having dorsally oriented eyes and nostrils, round pupils, a single internasal scale, no loreal scale, and smooth dorsal scales arranged in 15 rows at mid-body.1,2 The dorsal coloration itself is enough to identify this species from all other Amazonian snakes. It consists of 39–76 black transverse bands separated by light brown blotches in the vertebral region and red ones in the lateral region (Fig. 1).13 Some individuals may present red spots only in the posterior third of the body or lack them altogether.1 The head is dark brown with scattered red spots and the neck has a complete yellowish white ring. On the belly, the black bands projected from the dorsum can form rings or can be interrupted, giving the appearance of squares separated by white interspaces.1 This species differs from H. martii by having a complete pale ring around the neck as well as by having dorsal scales arranged in 15, instead of 17, rows at mid-body.4 From snakes of the genus Helicops, it differs by having smooth, instead of keeled, dorsal scales.5 From Micrurus surinamensis, it differs by having black rings not arranged in triads.

Figure showing an adult male of Hydrops triangularis

Figure 1: Adult male of Hydrops triangularis from Yasuní Scientific Station, Orellana province, Ecuador.

Natural history: Hydrops triangularis is an aquatic snake that inhabits rivers, streams, swamps, ponds, and lagoons in lowland rainforests with various degrees of human intervention.2,68 The species also occurs in human-modified environments such as in flooded grasslands, rice fields, and fish ponds.3,9 Triangle Watersnakes are active during the day or at night and typically in water or on mud along the bank.10 During the dry season, individuals can take refuge under the leaf-litter up to ~30 cm deep.11 Their diet consists primarily of fish, but also includes amphibians.3,10,12,13 When captured, the Triangle Watersnake thrashes the body, bites, produces cloacal discharges, and can regurgitate prey.7 Hydrops triangularis is an opisthoglyphous snake, meaning it has enlarged grooved teeth towards the rear of the maxilla and is midly venomous. Humans who have been bitten present local pain as well as nausea, headache, and mild coagulopathy.14,15 The breeding season is continous, with clutches consisting of 8–34 eggs.12,16

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Conservation: Least Concern Believed to be safe from extinction given current circumstances..17 Hydrops triangularis is listed in this category primarily because the species has a wide distribution spanning many protected areas. Furthermore, although it is a coral snake mimic prone to be killed on sight, this species appears to avoid encounters with humans due to its strong aquatic habits. Although there is no information on the population trend of the Triangle Watersnake, its population densities are expected to be declining alongside the decrease in water quality throughout the Amazonian river systems.

Distribution: Hydrops triangularis is widely distributed throughout the Amazon lowlands of Bolivia, Brazil, Colombia, Ecuador (Fig. 2), French Guiana, Guyana, Perú, Suriname, Trinidad, and Venezuela.18 In Ecuador, the species appears to be restricted to the tributaries of the Napo river in the northern Amazonian provinces, with a single record from the Río Bobonaza, a tributary of the Río Marañón.

Distribution of Hydrops triangularis in Ecuador

Figure 2: Distribution of Hydrops triangularis in Ecuador. See Appendix 1 for a complete list of the presence localities included in the map.

Etymology: The generic name Hydrops comes from the Greek words hydor (=water) and ops (=eye),19 and refers to the dorsally positioned eyes adapted to the aquatic lifestyle. The specific epithet triangularis comes from the Latin triangulus (=with three angles or corners)19 and refers to the almost triangular shape of the body of some individuals (when seen in cross section), since the dorsum is elevated and the venter is expanded when compressed. The holotype fits this descripton, but most living individuals are oval in cross section.

See it in the wild: Hydrops triangularis can be located at a rate of about once every few months in forested areas throughout the species’ area of distribution in Ecuador, especially along the lagoons and rivers of Limoncocha Reserve and Yasuní Scientific Station. These snakes are most easily detected by scanning the shallow water along muddy banks at night.

Authors: Juan Acosta-Ortiz,aAffiliation: Universidad de los Llanos. Villavicencio, Colombia. Alejandro González-Rojas,aAffiliation: Universidad de los Llanos. Villavicencio, Colombia. Andrés F. Aponte-Gutiérrez,bAffiliation: Grupo de Biodiversidad y Recursos Genéticos, Instituto de Genética, Universidad Nacional de Colombia, Bogotá, Colombia.,cAffiliation: Fundación Biodiversa Colombia, Bogotá, Colombia. and Alejandro ArteagadAffiliation: Khamai Foundation, Quito, Ecuador.

Photographer: Jose VieiraeAffiliation: Tropical Herping (TH), Quito, Ecuador.,fAffiliation: ExSitu, Quito, Ecuador.

How to cite? Acosta-Ortiz J, González-Rojas A, Aponte-Gutiérrez A, Arteaga A (2024) Triangle Watersnake (Hydrops triangularis). In: Arteaga A, Bustamante L, Vieira J (Eds) Reptiles of Ecuador: Life in the middle of the world. Available from: DOI: 10.47051/VPHQ3960

Literature cited:

  1. Albuquerque N, Lema T (2008) Taxonomic revision of the Neotropical water snake Hydrops triangularis (Serpentes, Colubridae). Zootaxa 1685: 55–66. DOI: 10.11646/zootaxa.1685.1.4.
  2. Dixon JR, Soini P (1986) The reptiles of the upper Amazon Basin, Iquitos region, Peru. Milwaukee Public Museum, Milwaukee, 154 pp.
  3. Beebe W (1946) Field notes on the snakes of Kartabo, British Guiana, and Caripito, Venezuela. Zoologica 31: 11–52.
  4. Pérez-Santos C, Moreno AG (1988) Ofidios de Colombia. Museo Regionale di Scienze Naturali, Torino, 517 pp.
  5. Pérez-Santos C, Moreno AG (1991) Serpientes de Ecuador. Museo Regionale di Scienze Naturali, Torino, 538 pp.
  6. Chippaux JP (1986) Les serpents de la Guyane Française. Institut Français de Recherche Scientifique pour le Développement en Coopération, Paris, 165 pp.
  7. dos Santos-Costa MC, Maschio GF, da Costa Prudente AL (2015) Natural history of snakes from Floresta Nacional de Caxiuanã, eastern Amazonia, Brazil. Herpetology Notes 8: 69–98.
  8. Cunha OR, do Nascimento FP (1994) Ofídios da Amazônia. As cobras da região leste do Pará. Boletim do Museu Paraense Emílio Goeldi 9: 1–191.
  9. Cortes-Ávila L, Toledo JJ (2013) Estudio de la diversidad de serpientes en áreas de bosque perturbado y pastizal en San Vicente del Caguán (Caquetá), Colombia. Actualidades Biológicas 35: 185–197.
  10. Field notes, Reptiles of Ecuador book project.
  11. Angarita-Sierra T (2014) Diagnosis del estado de conservación del ensamble de anfibios y reptiles presentes en los ecosistemas de sabanas inundables de la cuenca del río Pauto, Casanare, Colombia. Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales 38: 53–78. DOI: 10.18257/raccefyn.40
  12. Albuquerque N, Camargo M (2004) Hábitos alimentares e comentários sobre a predação e reprodução das espécies do gênero Hydrops Wagler, 1830 (Serpentes: Colubridae). Comunicações do Museu de Ciências e Tecnologia da PUCRS, Série-Zoologia 17: 21–32.
  13. Scartozzoni R (2009) Estratégias reprodutivas e ecologia alimentar de serpentes aquáticas da tribo Hydropsini (Dipsadidae, Xenodontinae). PhD thesis, Universidad de São Paulo, 160 pp.
  14. da Silva AM, Mendes VKG, Monteiro WM, Bernarde PS (2019) Non-venomous snakebites in the western Brazilian Amazon. Revista da Sociedade Brasileira de Medicina Tropical 52: 2–5. DOI: 10.1590/0037-8682-0120-2019
  15. Villca-Corani H, Nieto-Ariza B, León R, Rocabado JA, Chippaux JP, Urra FA (2021) First reports of envenoming by South American water snakes Helicops angulatus and Hydrops triangularis from Bolivian Amazon: A one-year prospective study of non-front-fanged colubroid snakebites. Toxicon 202: 53–59. DOI: 10.1016/j.toxicon.2021.09.003
  16. Braz H, Scartozzoni R, Almeida-Santos SM (2016) Reproductive modes of the South American water snakes : a study system for the evolution of viviparity in squamate reptiles. Zoologischer Anzeiger 263: 33–44. DOI: 10.1016/j.jcz.2016.04.003
  17. Nogueira CC, Gonzales L, Gagliardi G, Almendáriz A, Schargel W, Rivas G, Murphy J (2019) Hydrops triangularis. The IUCN Red List of threatened species. Available from: DOI: 10.2305/IUCN.UK.2019-3.RLTS.T176819A44950510.en
  18. Nogueira CC, Argôlo AJS, Arzamendia V, Azevedo JA, Barbo FE, Bérnils RS, Bolochio BE, Borges-Martins M, Brasil-Godinho M, Braz H, Buononato MA, Cisneros-Heredia DF, Colli GR, Costa HC, Franco FL, Giraudo A, Gonzalez RC, Guedes T, Hoogmoed MS, Marques OAV, Montingelli GG, Passos P, Prudente ALC, Rivas GA, Sanchez PM, Serrano FC, Silva NJ, Strüssmann C, Vieira-Alencar JPS, Zaher H, Sawaya RJ, Martins M (2019) Atlas of Brazilian snakes: verified point-locality maps to mitigate the Wallacean shortfall in a megadiverse snake fauna. South American Journal of Herpetology 14: 1–274. DOI: 10.2994/SAJH-D-19-00120.1
  19. Brown RW (1956) Composition of scientific words. Smithsonian Books, Washington D.C., 882 pp.

Appendix 1: Locality data used to create the distribution map of Hydrops triangularis in Ecuador (Fig. 2). Go to the section on symbols and abbreviations for a list of acronyms used.

ColombiaAmazonasLeticiaAponte-Gutierrez field notes
ColombiaCaquetáRío CaquetáNogueira et al. 2019
ColombiaCaquetáSan Juan del LosadaCortes-Ávila & Toledo 2013
EcuadorNapoCampo YuturiNogueira et al. 2019
EcuadorOrellanaEl CocaMHNG 2250.025; collection database
EcuadorOrellanaKm 135 en la vía Auca–Cononaco Nogueira et al. 2019
EcuadorOrellanaKm 28 vía Pompeya Sur–IroCisneros-Heredia 2003
EcuadorOrellanaParque Nacional YasuníCisneros-Heredia 2005
EcuadorOrellanaYarina LodgeReptiles of Ecuador book database
EcuadorOrellanaYasuní Scientific StationReptiles of Ecuador book database
EcuadorOrellanaYasuní, NPFNogueira et al. 2019
EcuadorOrellanaYasuní, SPFNogueira et al. 2019
EcuadorPastazaMontalvoOrtega-Andrade 2010
EcuadorPastazaRío PindoReptiles of Ecuador book database
EcuadorSucumbíosLimocochaAlbuquerque & de Lema 2008
EcuadorSucumbíosNWC clay lickReptiles of Ecuador book database
EcuadorSucumbíos LagartocochaNogueira et al. 2019
PerúLoretoIquitosMCZ 56054; VertNet
PerúLoretoMishanaNogueira et al. 2019
PerúLoretoMonte CarmeloAMNH 52354; VertNet
PerúLoretoParinariMCZ 178368; VertNet
PerúLoretoRequenaNogueira et al. 2019