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Predatory attack of a green anaconda ( Eunectes murinus ) on an adult human
... Our understanding of the biology of adult Green Anacondas has improved in recent years. There have been comprehensive studies of their mating system (Rivas and Burghardt, 2001;Rivas et al., 2007a), general natural history (Rivas, 2000;Rivas et al., 2007b), conservation and sustainable use (Rivas, 2007(Rivas, , 2010, predation (Rivas et al., 1999Rivas and Owens, 2000), diseases (Calle et al., 1994, foraging (Rivas, 1998(Rivas, , 2004, and demography (Rivas and Corey, 2008), along with notes on field techniques (Rivas et al., 1995;Raphael et al., 1996;Rivas, 2008). Adult anacondas live in shallow, stagnant water that is often covered by aquatic vegetation (Rivas, 2000;Rivas et al., 2007b). ...
... Average prey size observed in neonates is on par with the expected prey size found in adult snakes (Greene, 1992;Sazima, 1992), and it is not uncommon for large constrictors (Branch and Haacke, 1980;Rivas, 1998Rivas, , 2000Shine et al., 1998). Andreadis and Burghardt (2005) reported that neonatal Northern Water Snakes (Nerodia sipedon), given the choice, chose meal sizes close to 25% of their body mass. ...
Our knowledge of the biology of neonatal snakes has lagged behind that of adult animals, mostly due to the difficulty of finding and studying neonatal snakes in the wild. Traditional approaches view neonatal reptiles as miniature replicates of their adult counterparts. In this contribution, we present data on the natural history of neonatal Green Anacondas from opportunistic captures in the wild over a 17-year period, as well as from a brief study on captive-born radio-tagged individuals. Both approaches converge in presenting a picture of the ecology of neonatal anacondas showing many similarities between their natural history and that of adult anacondas in spite of the great size difference. The neonates' biology resembles that of adults, especially males, in their preference for birds in their diet, the relative prey size they choose, slow growth rates they experience, low feeding frequency, little mobility, and preference for similar habitats of stagnant, shallow water covered by aquatic vegetation. The conventional wisdom that neonatal reptiles are replicates of their adult counterparts seems to be largely on target in Green Anacondas. © 2016 by the American Society of Ichthyologists and Herpetologists.
... There have been comprehensive studies on the general natural history of the genus Eunectes [22,[33][34][35] including diet [36][37][38][39][40][41][42][43][44][45], diseases [46,47], habitat use and mobility [22,[30][31][32][33]44,45], allometric growth [48,49], and demography [22,50]. On the other hand, the conservation status of anacondas throughout their range is largely unexplored, although Eunectes species are protected from international trade by CITES's Appendix 2 [51][52][53]. ...
Anacondas, genus Eunectes, are a group of aquatic snakes with a wide distribution in South America. The taxonomic status of several species has been uncertain and/or controversial. Using genetic data from four recognized anaconda species across nine countries, this study investigates the phylogenetic relationships within the genus Eunectes. A key finding was the identification of two distinct clades within Eunectes murinus, revealing two species as cryptic yet genetically deeply divergent. This has led to the recognition of the Northern Green Anaconda as a separate species (Eunectes akayima sp. nov), distinct from its southern counterpart (E. murinus), the Southern Green Anaconda. Additionally, our data challenge the current understanding of Yellow Anaconda species by proposing the unification of Eunectes deschauenseei and Eunectes beniensis into a single species with Eunectes notaeus. This reclassification is based on comprehensive genetic and phyloge-ographic analyses, suggesting closer relationships than previously recognized and the realization that our understanding of their geographic ranges is insufficient to justify its use as a separation criterion. We also present a phylogeographic hypothesis that traces the Miocene diversification of anacondas in western South America. Beyond its academic significance, this study has vital implications for the conservation of these iconic reptile species, highlighting our lack of knowledge about Citation: Rivas, J.; De La Quintana, P.; Mancuso, M.; Pacheco, L.F.; Rivas, G.A.; Mariotto, S.; Salazar-Valenzuela, D.; Baihua, M.T.; Baihua, P.; Burghardt, G.M.; et al.
... Our understanding of the biology of adult green anacondas has been increasing in recent years. There have been comprehensive studies of its general natural history (Calle et al., 1994;Rivas et al., 2007b;Rivas, 2015;Rivas, 2020), predation (Rivas et al., 1999;Valderrama and Thorbjarnarson, 2001), diseases (Calle et al., 1994;Calle et al., 2001), notes on its foraging (Rivas, 1998;Rivas, 2004;, reproductive biology (Rivas and Burghardt, 2001;Rivas et al., 2007a;Rivas, 2023a), neonate biology (Rivas et al., 2016), allometric growth (Rivas, 2023b), and demography (Rivas and Corey-Rivas, 2008). From their foraging ecology, we know that adult anacondas are ambush hunters that may go for a long time without a meal, but when they do eat, they can take quite large meals. ...
Introduction: Trophic cascades can produce important effects on a community where some species may have strong effects on other parts of the community up, down the food chain, or both. Top predators are often controlled from the bottom-up by the abundance of their prey base while prey animals are often controlled from the top-down. Studies of trophic interactions in the tropics suggest that the trophic chains are longer because of the high productivity; and because of the high diversity there is abundant intraguild redundancy which results in weak interactions.
Methods: We studied the effect of bottom-up forces affecting the population of green Anaconda (Eunectes murinus) in the Venezuelan llanos; looking at net primary productivity, precipitation, and the abundance of an important prey item, Capybara (Hydrochaeris hydrochaeris).
Results: Our data show a strong interaction of these variables on the percentage of Anacondas that reproduce in a given year (here forth breeding ratio). In particular Capybara abundance has a strong effect. Capybara abundance itself is also under strong bottom-up influence determined by precipitation and Net Primary Productivity.
Discussion: These strong interactions are not what is expected from a tropical ecosystem. We also found an unexpected strong influence of precipitation and primary productivity on Anaconda breeding ratio not related to the abundance of Capybara, likely affecting abundance of other prey or affecting non-trophic variables. This later evidence supports the notion that there is redundancy in tropical food chains and, strong as the effect of Capybara bundance might be, Anacondas do not entirely rely on them.
... Our understanding of the biology of adult green anacondas has been increasing in recent years. There have been comprehensive studies of its general natural history (Calle et al., 1994;Rivas et al., 2007b;Rivas, 2015;Rivas, 2020), predation (Rivas et al., 1999;Valderrama and Thorbjarnarson, 2001), diseases (Calle et al., 1994;Calle et al., 2001), notes on its foraging (Rivas, 1998;Rivas, 2004;, reproductive biology (Rivas and Burghardt, 2001;Rivas et al., 2007a;Rivas, 2023a), neonate biology (Rivas et al., 2016), allometric growth (Rivas, 2023b), and demography (Rivas and Corey-Rivas, 2008). From their foraging ecology, we know that adult anacondas are ambush hunters that may go for a long time without a meal, but when they do eat, they can take quite large meals. ...
Introduction
Trophic cascades can produce important effects on a community where some species may have strong effects on other parts of the community up, down the food chain, or both. Top predators are often controlled from the bottom-up by the abundance of their prey base while prey animals are often controlled from the top-down. Studies of trophic interactions in the tropics suggest that the trophic chains are longer because of the high productivity; and because of the high diversity there is abundant intraguild redundancy which results in weak interactions.
Methods
We studied the effect of bottom-up forces affecting the population of green Anaconda (Eunectes murinus) in the Venezuelan llanos; looking at net primary productivity, precipitation, and the abundance of an important prey item, Capybara (Hydrochaeris hydrochaeris).
Results
Our data show a strong interaction of these variables on the percentage of Anacondas that reproduce in a given year (here forth breeding ratio). In particular Capybara abundance has a strong effect. Capybara abundance itself is also under strong bottom-up influence determined by precipitation and Net Primary Productivity.
Discussion
These strong interactions are not what is expected from a tropical ecosystem. We also found an unexpected strong influence of precipitation and primary productivity on Anaconda breeding ratio not related to the abundance of Capybara, likely affecting abundance of other prey or affecting non-trophic variables. This later evidence supports the notion that there is redundancy in tropical food chains and, strong as the effect of Capybara abundance might be, Anacondas do not entirely rely on them.
... The average prey size for adult females is 41 % (Rivas, 2020a;2015), so the average Titanoboa meal would have been in average 505 kg. Furthermore, data on the diet of anacondas suggests that anacondas can go for prey as large as 146 % of its body weight (Rivas, 1998). If a large Titanoboa, at 1,232 kg, had been able to attack prey of this size, this prey would had weighed 1,799 kg. ...
The maximum size that snakes can reach has been a matter of long held debate until the discovery of Titanoboa cerrejonensis (Boidae). It was an aquatic predator that lived 60–58 million years ago in what is currently eastern Colombia, occupying tropical swamps. It was calculated to measure 12.82 metres and it was speculated that it grew so much due to a warmer planetary weather. Its life history and ecology are speculated to be very similar to that of current day anacondas. Using data from a long-term study involving hundreds of green anacondas Eunectes murinus, this study makes inferences about aspects of the natural history of T. cerrejonensis that perhaps will not be easily available by studying the fossil record. Drawing parallels with anaconda's biology, I estimate that a non-breeding female T. cerrejonensis weighed approximately 1,232 kg, and 1,465 kg when pregnant. It would have started breeding at 480 cm SVL, weighing 95 kg. New-born Titanoboa were between 181 and 215 cm. Its average meal was estimated to be 505 kg, with a potential maximum of 1,799 kg. I estimate that Titanoboa had a growth rate of 0.046 mm/day compared with 0.036 in anacondas; which does not support the notion that it grew more due to a warmer planet. Although the results are largely speculative, they help give a better idea of what the life of an extinct snake was like. Keywords: Gigantism, prey size, reproductive biology, life history, palaeothermometer, giant snake, allometry, palaeoecology
... Green anacondas feed mostly on small to medium-sized mammals but may occasionally prey on larger mammals such as deer ( Kolesnikovas et al., 2007;Puorto and França, 2009). Because of their large size (up to 10m snout-vent-length [SVL]), green anacondas can pose dangers to humans (Rivas, 1998). Boa constrictor constrictor is commonly found in dry and mesic habits in Brazil. ...
Boids are large, constrictor snakes that feed mostly on mammals, reptiles, and birds. These animals are commonly raised as pets, and their improper handling can favor the emergence of fungal infections, which can lead to dermatological diseases that are undiagnosed in nature. Here, we isolate and identify the filamentous fungi that compose the mycobiota of the scales of boid snakes kept in captivity at the Biological Museum of the Butantan Institute. Thirty individuals of four species were evaluated: four Eunectes murinus, twelve Boa constrictor constrictor, seven Corallus hortulanus, and seven Epicrates crassus. Microbiological samples were collected by rubbing small square carpets on the snake scales. We isolated five genera of fungi: Penicillium sp. (30%), Aspergillus sp. (25%), Mucor sp. (25%), Acremonium sp. (10%), and Scopulariopsis sp. (10%). Approximately half of the snakes evaluated had filamentous fungi on the scales, but only 12% of the individuals were colonized by more than one fungal genus. We found no dermatophytes in the evaluated species. Our results provide an overview of the fungal mycobiota of the population of boids kept in the Biological Museum, allowing the identification of possible pathogens.
... al. (2008), Lamonica et. al. (2007), Müller (1970), Petzold (1983) Rivas (1998, 2000, Rivas and Corey (2008), Rivas and Burghardt (2001), Rivas and Owens (2000), Rivas et. al. (1995Rivas et. ...
A review of the taxonomy of the New World boids finds several genera as currently recognized to be paraphyletic. There are available genus names for those species within genera that have been found to be composite, should they be split to ensure monophyletic genera. The only potential exception to this is within the genus Eunectes Wagler, 1830 as currently recognized. There is a strong argument in favor of splitting the so-called Yellow Anacondas away from the so-called Green Anacondas, at the genus level as a result of clear and consistent differences between the relevant taxa. This paper formalizes this division by taking a conservative position and naming and defining a new subgenus, Maxhoserboa subgen. nov. for the Yellow Anaconda and related species.
Human relationships with giant snakes are complex and evolving in unusual directions. Four or five of the largest snakes are human predators. Humans, however, are predators on the snakes, hunting them for food and skins and used in the leather industry. During much, if not all, of human history, we were sympatric with several of the most massive snakes, and these animals undoubtedly were selection factors in our evolution. They preyed upon us, we killed and ate them, and they were one of our competitors for much of the same protein. Today, the relationship has evolved, while we continue to hunt snakes for skins, we also keep them as pets and most surprisingly breed them for unusual color patterns and keep them as living works of art. Unfortunately, we have allowed them to escape into North America and become invasive. They have altered the species composition of natural communities and threaten endangered species. Recently, science has realized giant snake physiology may hold the key to controlling diabetes.
We here revisit the natural history of Green Anacondas and give our personal view of how Ecotourism can affect their existence.
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