Peters’ Watersnake (Helicops petersi)

Reptiles of Ecuador | Serpentes | Colubridae | Helicops petersi

English common names: Peters’ Watersnake, Peters’ Keelback, Spiral Keelback.

Spanish common name: Culebra acuática de Peters.

Recognition: ♂♂ 66.5 cmMaximum distance from the snout to the tip of the tail. Snout–vent length=41.5 cm. ♀♀ 54.4 cmMaximum distance from the snout to the tip of the tail. Snout–vent length=43.4 cm.. ¹ Helicops petersi can be distinguished from most Amazonian snakes by having dorsally oriented eyes and nostrils, a single internasal scale, round pupils, and keeled dorsal scales arranged in 21 (rarely 23) rows at mid-body.^1,2 The dorsum is grayish brown with a series of faint dark blotches (Fig. 1).² Females differ from males by having a shorter tail with fewer subcaudal scales.² Helicops petersi is most similar to, and is often confused with, H. pastazae, from which it differs by having a lower number of dorsal scale rows, a pointed snout, and a different color pattern.² In H. petersi the lateral blotches are about the same size as the mid-dorsal ones (rather than distinctly smaller), and the dark ventral blotches are interrupted by a longitudinal pale stripe (absent in H. pastazae).² Helicops petersi differs from H. angulatus, H. hagmanni, Hydrops martii, and H. triangularis by having keeled dorsal scales arranged in 21–23 rows at mid-body, more than 67 subcaudal scales, and a non-banded pattern.^2,3

Figure showing variation among individuals of Helicops petersi

Figure 1: Individuals of Helicops petersi from Suchipakari Lodge () and Río Bigai Reserve (), Orellana province, Ecuador.

Natural history: Helicops petersi is a semi-aquatic snake that inhabits lentic bodies of water in rainforests with various degrees of human intervention as well as in peri-urban areas, including large cities such as Tena.^4,5 This species is found in tributaries of large lakes and rivers, including small streams and fast-flowing whitewater rivers, but also in flooded soccer courts.^4,5 Peters’ Watersnakes are nocturnal, but can occasionally be seen moving during the daytime.^5–7 They are aquatic and can be found at different depths. When in shallow waters, individuals usually have the body submerged and part of the head above the surface.⁵ These snakes move not only in water but also on rocks, mud, and sand close to water bodies.^5–7 During the daytime, they have been found buried in the sand besides rivers.¹ Peters’ Watersnakes are sit-and-wait predators that feed mainly or exclusively on fish.⁴ Individuals have been captured in fish nets, which could indicate that members of this species are opportunistic predators of trapped fish.⁴ Their typical defensive behavior consists of making an S-coil, flattening the body and head dorsoventrally, and striking.⁵ When manipulated, they rotate the body, bite, and produce cloacal discharges.⁵ This species is probably oviparous. One gravid female contained 12 small eggs.¹

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Conservation: Vulnerable Considered to be facing a high risk of extinction in the mid-term future.. Helicops petersi is proposed to be included in this category, instead of Near Threatened,⁴ because the species is range-restricted (~9,800–10,916 km²; Fig. 2), its habitat is severely fragmented, and the rivers where it occurs are declining in quality due to pollution. The habitat of H. petersi coincides with the most fragmented segment of the Ecuadorian Amazon rainforest and the rivers where it occurs are currently being destroyed and polluted by open-pit gold mining operations. Although there is no information on the population trend of the species, its numbers are expected to be declining alongside the increase in gold mining activities along the rivers Anzu, Tena, and Napo.

Distribution: Helicops petersi is endemic to an area of approximately 10,916 km² in the upper watershed of the Napo river in eastern Ecuador (Fig. 2).

Figure 2: Distribution of Helicops petersi in Ecuador. See Appendix 1 for a complete list of the presence localities included in the map. The star corresponds to the type locality: Río Misahuallí.

Etymology: The generic name Helicops, which comes from the Greek words helix (=turned) and ops (=eye),⁸ refers to the direction of the eyes in this group of snakes, oriented not directly outwards, but obliquely upwards.^9,10 The specific epithet petersi honors American herpetologist James A Peters (1922–1972), in recognition of his contributions to expanding the knowledge on Neotropical reptiles, particularly those from Ecuador.

See it in the wild: Peters’ Watersnakes can be located at a rate of about once every few months throughout the species’ area of distribution, especially along slow-moving whitewater rivers. The area having the greatest number of recent observations is Río Misahuallí, near the city Tena, Napo province. The snakes are most easily found at night by walking along rocky river shores.

Acknowledgments: This account was published with the support of Secretaría Nacional de Educación Superior Ciencia y Tecnología (programa INEDITA; project: Respuestas a la crisis de biodiversidad: la descripción de especies como herramienta de conservación; No 00110378), Programa de las Naciones Unidas (PNUD), and Universidad San Francisco de Quito (USFQ).

Author: Alejandro Arteaga^aAffiliation: Khamai Foundation, Quito, Ecuador.

Photographers: Jose Vieira^bAffiliation: Tropical Herping (TH), Quito, Ecuador.^,^cAffiliation: ExSitu, Quito, Ecuador. and Amanda Quezada^aAffiliation: Khamai Foundation, Quito, Ecuador.

How to cite? Arteaga A (2024) Peters’ Watersnake (Helicops petersi). In: Arteaga A, Bustamante L, Vieira J (Eds) Reptiles of Ecuador: Life in the middle of the world. Available from: www.reptilesofecuador.com. DOI: 10.47051/UNSB1612

Literature cited:

Duellman WE (1978) The biology of an equatorial herpetofauna in Amazonian Ecuador. Publications of the Museum of Natural History, University of Kansas 65: 1–352.
Rossman DA (1976) Revision of the South American colubrid snakes of the Helicops pastazae complex. Occasional papers of the Museum of Zoology, Louisiana State University 50: 1–15.
Schöneberg Y, Köhler G (2024) Distribution and identification of the species in the genus Helicops Wagler, 1830 (Serpentes, Colubridae, Xenodontinae). ARPHA Preprints 1: e67869. DOI: 10.3897/arphapreprints.e67869
Cisneros-Heredia DF, Almendáriz A, Valencia J (2017) Helicops petersi. The IUCN Red List of threatened species. Available from: www.iucnredlist.org. DOI: 10.2305/IUCN.UK.2017-2.RLTS.T15179117A15179121.en
Field notes, Reptiles of Ecuador book project.
Photo by Cristina Teruel Vilar.
Photo by Jimmy Velasteguí.
Brown RW (1956) Composition of scientific words. Smithsonian Books, Washington D.C., 882 pp.
Wagler JG (1830) Natürliches System der Amphibien: mit vorangehender Classification der Säugetiere und Vögel: ein Beitrag zur vergleichenden Zoologie. J.G. Cotta'scchen, München, 354 pp. DOI: 10.5962/bhl.title.58730
Duméril AMC, Bibron G, Duméril AHA (1854) Erpétologie générale ou Histoire Naturelle complète des Reptiles. Librairie Encyclopédique de Roret, Paris, 780 pp. DOI: 10.5962/bhl.title.45973

Appendix 1: Locality data used to create the distribution map of Helicops petersi in Ecuador (Fig. 2). Go to the section on symbols and abbreviations for a list of acronyms used. Asterisk (*) indicates type locality.

Country	Province	Locality	Source
Ecuador	Napo	Finca Fischer	TCWC 65022
Ecuador	Napo	Misahuallí	Photo by Diego Piñán
Ecuador	Napo	Río Cotopino	Rossman 1976
Ecuador	Napo	Rio Misahuallí*	Rossman 1976
Ecuador	Napo	Suchipakari Lodge	This work
Ecuador	Napo	Tena	iNaturalist
Ecuador	Orellana	Concepción	Rossman 1976
Ecuador	Orellana	Mouth of Río Guataraco	Rossman 1976
Ecuador	Pastaza	Alpayacu	Rossman 1976
Ecuador	Pastaza	Muyu Rainforest Reserve	iNaturalist
Ecuador	Pastaza	Reserva Río Anzu	This work
Ecuador	Pastaza	Río Arajuno, headwaters of	Rossman 1976
Ecuador	Sucumbíos	Puerto Libre	Duellman 1978
Ecuador	Sucumbíos	Río Aguarico	Torres-Carvajal et al. 2019
Ecuador	Sucumbíos	Santa Cecilia	Duellman 1978