FAMILY BOIDAE BOAS AND ANACONDAS FAUNA PARAGUAY

FAMILY BOIDAE - BOID SNAKES
Five species in this family arranged into three genera Boa, Epichrates and Eunectes. Snakes in this family are constrictors and include some of the largest and most robust of the world´s snakes. There are three subfamilies in this family, only one of which occurs in Paraguay, the Boinae.
Boids have the left lung greatly enlarged, some 30 to 80% larger than the right and the ventral scales are moderately large.

SUBFAMILY BOINAE - BOAS AND ANACONDAS
Members of this subfamily lack teeth on the premaxilla and supraorbital bones. The subcaudal scales are single and there is no tracheal lung. Viviparous, bearing live young.

Key to Adults of Paraguayan Boas

1a Dorsal pattern with large rounded spots black, darker than background colour................................ Eunectes 2
1b Dorsal pattern with large rounded spots paler than background colour.......................................................... 3

2a Background colour tending towards yellowish, but occasionally greenish or brown. Dark dorsal spots consisting of two fused circles, giving them a somewhat elongated appearance. Distributed along the courses of the Paraguay, Pilcomayo and Paraná rivers (Ñeembucú and Misiones) ........................................ Eunectes notaeus
2b Background colour tending towards greenish, but occasionally yellowish or brown. Dark dorsal spots consisting of clearly-defined rounded circles. Distributed in northern and eastern Oriental region........................................................................................................................................... Eunectes murinus

3a Head elongated and not strongly triangular, with dark longitudinal lines on dorsal surface. Base colour of dorsal surface brownish with orange dorsal spots. Dorsal spots fairly small, thinly and evenly edged darker. Oily or "rainbow" iridescence to scales visible in live or recently dead individuals. .................................. Epicrates 4
3b Head strongly triangular and uniform or mottled on dorsal surface, never with dark longirudinal lines. Base colour of body variable, may be brown, grey, blackish or yellowish. Dorsal spots large, broadly and unevenly "bracketed" darker No iridescence on scales. ............................................................................... Boa constrictor 5

4a Short dark postorbital stripe behind the eye. Anterior dorsal scale rows >40, interrictals <24. Loreal scale divided. Frontal scale reduced or absent. Prefrontals coupled. Distributed in Dry Chaco west of the Rio Paraguay.................................................................................................................................... Epicrates alvarezi
4b Long dark stripe from nose passing through the eye to the rear of the head. Anterior dorsal scale rows <40, interrictals >24. Loreal scale single. Frontal scale as long as it wide. Prefrontals with V-shaped arrangement. Distributed in grasslands and Atlantic Forest in the eastern Oriental region............................... Epicrates crassus

5a Patternation clean and uniform. Distributed in northern and Oriental region east of the Rio Paraguay................................................................................................................................ Boa constrictor amarali
5b Patternation strongly mottled and marbled, less clearly defined. Distributed in Dry Chaco west of the Rio Paraguay ........................................................................................................................... Boa constrictor occidentalis

REFERENCES
Caccialli P 2010 - Guía para la Identificación de 60 Serpientes del Paraguay - Guyra Paraguay, Asunción.
Fouquette MJ (unpublished) - Synopsis of Recent Reptiles to Genus - Arizona University
Passos P, Fernandes R 2008 - Revision of the Epicrates cenchria complex (Serpentes: Boidae) - Herpetological Monographs 22 p1-30.
Whitfield P Ed.1984 - Longman Illustrated Animal Encyclopedia - Guild Publishing, London.