Reptile & Amphibian Forums

Over the last several months I have been reading websites, magazine articles, and other forum posts discussing various biological and taxonomic aspects of the least known species of the anaconda complex, Eunectes beniensis. I guess my main concern is the large amount of erroneous information that is being passed around with regards to this relatively new species. I would like to try and clarify some of the mystery out there about this species and hopefully correct some of this misinformation.

Lutz Dirksen was the first individual to notice a different type of anaconda in the floodplain areas of northeastern Bolivia in 1994. This species was later described by Dirksen and officially recognized as a new species in 2002. The species name is derived from the State of Beni in the country of Bolivia. It is named so as Beni was the location of the discovery of the holotype specimen, or the original specimen from which a new species is described. E. beniensis was originally thought to be a possible hybrid between E. murinus and E. notaeus, but closer study showed that this was not the case. While the ranges of E. murinus and E. notaeus do overlap in some areas, there have be no specifically identified specimens showing intermediate traits captured in these areas. Additionally, while the northern geographical range of E. beniensis does slightly overlap that of E. murinis, no range overlap is known to occur between E. beniensis and E. notaeus.

One major misconception that occurs with E. beniensis is in regards to the size of this species. I have seen numerous references in magazine articles and internet sites stating the average length at 4 to 5 feet. I am not sure where the data for this comes from, but I have not seen anything in the scientific literature to support it. Just looking at the Type Series alone, which is represented by 3 sub-adult to adult male specimens, the average male in just this small group is between 6 and 7 feet. The one female included in the Type Series measured 10.5 feet. Having spent a fair amount of time researching sources of information on E. beniensis, I have come across a dozen or so photographs of captured specimens in the field. All are being held by people, all full body photos, and therefore relatively easy for length estimates. Most appear to be in the 6 to 8 feet range with a few in the 8 to 10 feet range. There are a couple that appear to be easily 10 to 12 feet. Dirksen estimates from all of the data he has gathered that female E. beniensis probably reach 13 to 14 feet, and goes on to say, possibly longer. With several 10 to 12 foot individuals in just a handful of known specimens, I would not be surprised at all if really large female E. beniensis hit the 15 feet mark. This makes E. beniensis the second largest of the 4 species of anaconda, surpassing E. notaeus and E. deschauenseei in average length.

Most of the information I have gathered comes from papers written by Lutz Dirksen and Wolfgang Bohme, and these two gentlemen have added immensely to the body of knowledge with respect to all of the anaconda species, but especially E. beniensis.

Kelly

Kelly do you have any pictures by any chance ?
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Thanks,

Frank Roberts

Great post.........just suprised there was no pics.
Mike

I hesitate to post any photos without the permission of the photographer, but I do have a couple that I have been given second-hand permission to post. These two photos are of the same anaconda and one can immediately see that this is without a doubt E. beniensis.

In the head photo, it is quite apparent that the oculars and supralabials are in contact and not separated by suborbital scales as in E. murinus. In the larger body photo, the ground color is olive brown with greatly extended lateral markings that are all solid in color with no lighter colored centers. This is a classic example of E. beniensis. I would estimate the length of this snake at around 10 feet.

I had a photo many years ago, that was lost in a computer crash, of a beniensis that was about 12 feet that was captured in northern Bolivia. It was the largest example of beniensis that I have actually seen to date. There were 4 guys holding it stretched out and the caption was just anaconda from north Bolivia. I don't believe they were aware that it was anything other than a green anaconda, but it was identical to the one in these attached photos. There was no doubt about it's identification. If you picture search the web under Beni anaconda or Bolivia anaconda you can see some of the pictures of E. beniensis that are out there. Be careful however, because a large number of them are of E. murinus so you will need to look closely for proper identification. I think the reason that most of photos are of smaller individuals is that they are being caught in the more easily accessible areas where the younger snakes are hanging out. That photo of the largest specimen appeared to be in a more inaccessible area, and by the short story, was not a guided tour.

I would also be interested in any other photos anyone comes across of E. beniensis, especially photographs of larger specimens. Although they occur within a relatively restricted range, they do not appear to be a rare snake within that range.
Thanks,

Kelly

Are you aware of any differences in diet or habitat choices by this species, and is this snake protected as eunectus is in other countries of south america.

I would not think the diet would be much different than that of the greens that inhabit the llanos of Venezuela. These two habitats are somewhat similar and would have similar prey species. The river floodplains that form the preferred habitat of beniensis are not all that different from the flooded savannas in Venezuela. However, E. murinus that inhabit rainforest stream systems would be a little different matter.

I don’t believe Bolivia was much into protecting indigenous reptile species until the early 1990’s if I remember correctly. Since then, they have followed some CITES protection strategies and strictly limit exportation of wildlife.

Kelly

Kelly,

Thank you for posting this. I too have been banging my head against the wall when I see information like you stated above mentioned. Clearly the people who write this have failed to read the Dirksen reports, or are mistaking meters for feet.