An Unstoppable Anaconda Invasion in Florida? What Slate Got Wrong.
Photo By Dave Lonsdale, Wikimedia
by Dr. David Steen from his Living Alongside Wildlife blog.
Last week Slate ran a piece in their Wild Things blog entitled, “Green
Anacondas in the Everglades: The Largest Snake in the World has Invaded the
United States.” Obviously the sensational headline caught my attention as
did the subtitle, which refers to this invasion as "unstoppable." However,
after reading the actual article I realized that it was basically just a
smattering of anecdotes. That makes for a fun story and some interesting
conversations, but unfortunately it is too easy to interpret the article as
news. Let me be clear: There is virtually no evidence that a population of
anacondas exists in Florida.
Curiously, Slate does not mention that the two individuals that provided
the bulk of their anaconda information are affiliated with the Skunk Ape
Museum in Ochopee, Florida (the facility is instead described as a “roadside
zoo” or the “Trail Lakes Campground”). The Skunk Ape, if you’re not
familiar, is the South Florida equivalent of Bigfoot. For what it’s worth,
the official website of the Skunk Ape Museum unequivocally states that there
are between 7-9 Skunk Apes living in the Everglades. Now, just because
someone believes that there is a population of Skunk Apes living in the
Everglades does not mean that we can or should discount everything they say,
but it does indicate that they probably have different standards than most
people when deciding what is circumstantial evidence and what is proof when
it comes to determining whether an animal population exists.
If you give the article a careful read, the entire premise that there is
a breeding population of Green Anacondas (Eunectes murinus) in the
Everglades boils down to: 1) ten years ago a juvenile Green Anaconda was
found in the Everglades; the snake didn’t eat anything and died, 2) another
Green Anaconda was later found in the region and finally, 3) lots of people
around the Everglades have seen large snakes they did not identify but that
possibly could have been Green Anacondas.
I don't know about you, but this does not convince me that anacondas
have invaded South Florida.
The worst (and incredibly ironic) part of the article is that it
repeatedly suggests that the well-publicized concern about the Burmese
Python in Florida is largely a result of media-hype while the real problem
(i.e., Green Anacondas) is overlooked. The fact that there is a large,
reproducing population of Burmese Pythons in Florida is well-documented:
thousands have been found including everything from juveniles to giant
adults with 87 eggs inside. This population has been the subject of several
large and ongoing research projects that have produced numerous scientific
papers. For example, a recent paper in the Proceedings of the National
Academy of Sciences described how mammal populations have crashed as the
Burmese Python population expanded (and presumably, as they ate many of the
mammals).
On the other hand, documentation of the Green Anaconda "invasion"
basically consists entirely of the majorly hyped-up Slate article, which
hints that the snakes can get as wide as hula-hoops (they can’t) and
probably eat people.
The irony boggled my mind. Because I only have very little first-hand
experience with large invasive snakes, I contacted some of my friends and
colleagues that study these Florida reptiles for their perspectives on the
article. Unfortunately, I can’t repeat most of their reactions here (this is
a family-friendly blog after all). But, fortunately Dr. J.D. Willson did
provide a printable response. J.D. is an Assistant Professor at the
University of Arkansas and has authored numerous articles about Burmese
Pythons in Florida. Notably, he is also co-author of the new book, Invasive
Pythons in the United States: Ecology of an Introduced Predator. I figured
he could set the record straight.
J.D. replied, “Although there certainly has been a strong dose of
sensationalism about the Burmese Python issue from the media, our research
suggests that the problem is severe and should be considered a major threat
to the Everglades. Over the past decade, Burmese Pythons have spread over an
area of at least 4,000 square miles and including all of Everglades National
Park and Big Cypress National Preserve. They also appear to have wiped out
mammals such as rabbits, raccoons, and bobcats in the heart of the
Everglades National Park. Over 2,000 of these snakes have been captured and
our research shows that this is just a tiny fraction of the overall population…"
On the other hand…
“…We currently have no reason to suspect that anacondas are established in
South Florida. This species certainly is kept in captivity and apparently
escaped or released pets have been found. However, the small number of
individuals that have been found were far apart and there has been no
evidence of reproduction or of a ‘hotspot’ where sightings are concentrated.”
Is it possible that there is a population of Green Anacondas prowling
through the isolated marshes of the Everglades? Yes. When the author notes
that even big snakes can effectively evade detection in the Everglades, he
is completely correct. In addition, Burmese Pythons were already firmly
established in Florida before there was indisputable proof that they
represented a reproducing population. But there is really no compelling
reason to think there is a Green Anaconda population in the Everglades; a
grand total of four Green Anacondas have ever been confirmed in Florida,
this despite a large-scale reporting and monitoring system that was recently
put in place to track the presence of large invasive snakes there. If we use
four animals as evidence of a population, for consistency we then also have
to believe that just about every other exotic animal ever found in the state
also represents an established population, with the possible exception of
Skunk Apes.
But what about all the large snakes people have reported seeing in the
Everglades? This phenomenon is not unique to that region. Anyone that has
spent any time answering snake questions knows that in general, people are
not very good at identifying snakes and tend to exaggerate both their size
and their potential to inflict bodily harm.
Before closing, I want to address two specific points from the original
article. First, the juvenile anaconda that was captured in the Everglades
did not eat and later died. Is this compelling evidence that it was a wild
snake and therefore that anacondas are breeding in the Everglades?
Anyone that has experience with captive snakes knows that some are picky
eaters, perhaps especially when said snake is an exotic species from a
faraway land with unique habitats (like, for example, the Amazon). If we are
to believe that a snake that did not eat is evidence that it is wild, should
we then also believe that the only other individual Green Anaconda captured
in the Everglades and mentioned in the article is actually an escaped
captive because it did eat?
Second, the original article argues that the Burmese Python invasion is
no big deal compared to an invasion of Green Anacondas because fire ants
kill pythons but not anacondas. Laboratory studies have confirmed that fire
ants (i.e., Solenopsis invicta) are capable of penetrating reptile eggs,
including those of Burmese Pythons. In addition, some have suggested that
egg-laying reptiles are more susceptible to being killed by fire-ants than
are reptiles that give birth to live young. Fire ants have even been
implicated in the declines of some snakes in the southeastern United States,
like Southern Hognosed Snakes (Heterodon simus) and Kingsnakes (Lampropeltis
getula). But, these are just ideas. There is no evidence that fire ants are
influencing the population growth of any reptile.
To say with confidence that fire ants are limiting the population growth
of Burmese Pythons we would need to have some kind of idea regarding how
many young Burmese Pythons are being produced and how many are being killed
by fire ants and this information is not available to us. The article notes
that a single captive Burmese Python and her eggs were killed by fire ants
and this is interesting. But, it does not suggest that the wild population
is being affected at all. To put it another way, a paper published in 1989
identified 10 confirmed cases of fire ants killing human beings in Florida
(and there surely have been more cases since that publication). I don’t
think anyone would take that information and then suggest that fire ants are
limiting human population growth.
The possibility of Green Anacondas secretly prowling and reproducing
throughout the Everglades is a fun topic to discuss around the campfire.
But, it doesn’t stand up to scientific scrutiny. I wish Slate had made that
clear.
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Some Relevant Scientific Papers:
Diffie, S., Miller, J, & Murray, K. (2010). Laboratory Observations of Red
Imported Fire Ant (Hymenoptera: Formicidae) Predation on Reptilian and Avian
Eggs Journal of Herpetology (44), 294-296 DOI: 10.1670/08-282.1
Dorcas ME, Willson JD, Reed RN, Snow RW, Rochford MR, Miller MA, Meshaka WE
Jr, Andreadis PT, Mazzotti FJ, Romagosa CM, & Hart KM (2012). Severe mammal
declines coincide with proliferation of invasive Burmese pythons in
Everglades National Park. Proceedings of the National Academy of Sciences of
the United States of America, 109 (7), 2418-22 PMID: 22308381
Rhoades RB, Stafford CT, & James FK Jr. (1989). Survey of fatal anaphylactic
reactions to imported fire ant stings J Allergy Clin Immunol., 84, 159-162
DOI: 10.1016/0091-6749(88)90373-9
