The following copyrighted material is intended for individual use of the researcher, and may not be copied or distributed without written permission from the copyright holder. You may use it for non-profit scholarly purposes. The reference: Rivas, J. A. and R. Y Owens. 2000. Eunectes murinus (Green anaconda): cannibalism. Herpetological Review 31: (In press)

Eunectes murinus (Green anaconda): Cannibalism (click here for a pdf version)

One instance of cannibalism in the green anaconda (Eunectes murinus) has been reported in the literature (O’Shea, M. T. 1994. Herpetol. Rev. 25: 124). This observation involved a female eating a smaller conspecific of unknown sex. Here we report three other cases of female anaconda predation on conspecifics. These observations occurred during the breeding (dry) season in the Venezuelan llanos, Distrito Muñoz, Apure State, (7º 30' N and 69º 18' W).

The first observation involved a large female (434.7 cm total length (TL) and 40 kg) that was caught in 27 April 1995 next to a breeding aggregation (Rivas 1999. Life history of the green anacondas with emphasis on its reproductive biology. Ph.D. dissertation at the University of Tennessee, 215 pages), but not participating in it. The snake had the engorged stomach that indicates a recent meal. After putting her in a cage, she regurgitated a male anaconda (42 cm tail length, 283 cm estimated TL; 5.7 kg, Figure 1). On the 28th of May 1996, at the end of the breeding season, we discovered another female constricting a medium-sized male (230 cm TL; 5kg). The male was dead by the time we found it, and the female (370 cm estimated TL) managed to escape when we tried to capture her. Judging by the girth and overall condition of the snake, she was most likely breeding, and probably had just recently finished her mating activity. Lastly, in 18 March 1997 we collected a feces sample that contained anaconda scales. The sample was from a female anaconda (300 cm. TL, 14.8 kg) that was breeding that season.

All the records of cannibalism in green anaconda involve cannibalistic females, and both times the sex of the cannibalized individual has been known it has been male. This asymmetry is probably a consequence of the strong sexual size dimorphism found in the species; where females are much larger than males (Rivas op. cit.). Green anacondas become concentrated around the more permanent water sources during the dry season, and at this time breeding occurs (Rivas op. cit.). Male anacondas looking for water and/or females appear to be especially vulnerable to cannibalism by females. After mating, pregnant females do not eat for seven months (Rivas op cit.). It is possible that breeding females eat their mating partners in order to help them survive the long fast associated with pregnancy

Acknowledgement: We thank the Wildlife Conservation Society and the National Geographic Society for funding this research. COVEGAN allowed us to work on their land. We also thank G. M. Burghardt for editorial comments on the manuscript

Jesús A. Rivas. Graduate program in Ethology, Dept. of Ecology & Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996-0900. Renee Y. Owens, Vegueros Wildlife Biology, 17126 Jamul CA 91935.

Current address for correspondence : 17126 Lawson Valley Road, Jamul CA 91935.


Figure 1 Females anaconda regurgitating a male (notice the hemipenis in the shot) Photo Tony Rattin