Invasive Burmese pythons eat their way through southern Florida: the unexpected effect on our health.

Kaley Fournier (Natural Resources Conservation), Edward Hines (Environmental Science), and Nicholas Stevenson (Animal Science).



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It starts with a headache. Perhaps you develop a fever and become physically ill. You chock it up to the flu and try to let it run its course. What you don’t know; you’ve been infected. Once symptoms start to show, death is expected within 2 to 10 days. Even if you get to a doctor in time to save your life, you will most likely be left with mental and physical disability (Center for Disease Control and Prevention, 2016). Where exactly did you come across such a dangerous virus? Your own backyard. Eastern Equine Encephalitis virus is one of the most severe mosquito-transmitted diseases in the United States with approximately 33% mortality and significant brain damage in most survivors (CDC, 2018). The cause of this EEE scare is something unpredictable. The cause can be traced back to something much larger than a mosquito, Invasive Burmese pythons. This snake has slithered its way through southern Florida, devouring native wildlife in its path. This sharp decrease in wildlife populations has forced a change in the animals in which mosquitoes find their dinner. A change to disease ridden animals. Once mosquitos feast on infected hosts, they too become infected. This leaves us with not only wildlife populations to worry about, but also our own health.

Because of Florida’s tropical climate and swaps, it is the perfect home for many exotic, or non-native, species to thrive. Burmese pythons (Python bivittatus) are considered invasive species in southern Florida, because they are an exotic species that have had many negative effects on this new environment. This particular breed of snake is native to the tropical south and southeast Asia. The Burmese python most likely first arrived in Florida as part of the exotic pet trade, over time making their way into the Everglades due to deliberate release from overwhelmed owners or by accidental escape from their homes. Invasive species such as this disrupt the ecosystem by preying on native species and outcompeting them for food or other resources. Burmese pythons hunt their prey using cover and camouflage, which is plentiful in the Everglades (Walters et al., 2016). Burmese pythons are generalists and don’t rely on a specific prey species. Because of this behavior factor, they pose a huge threat to native mid-sized mammals (Harvey et al., 2008). The united states banned the importation of Burmese pythons under the Lacey Act in January 2012 (U.S Fish and Wildlife Service, 2012). However, their population continues to grow in south Florida. A typical female breeds every other year, producing a clutch of between twenty and fifty eggs, and can live for twenty years or more. More than 2,000 pythons have been captured in the U.S. since 2005 (Dorcas & Willson, 2011). Researchers estimate that between 30,000 and 300,000 Burmese pythons find their home in southern Florida (Snow et al. 2007). Their population is established in southern Florida but they have been spotted as far north as Jacksonville, Chipley, and even Winokur Georgia (EDDmapS, 2018). Many small mammal populations, such as rabbit and raccoon, have been on the decline since the pythons were introduced into the environment during the 1980s (Willson, 2017). Even larger mammals such as deer and bobcat have felt the effects of the invasion of the Burmese python on their population sizes. This decrease in mammal populations has led to a shift in blood meal hosts for naive mosquitoes to pathogen carrying animals. This is a public health concern as this puts humans at a greater risk for contracting mosquito-transmitted diseases. Invasive Burmese pythons pose a threat not only to the native wildlife of southern Florida, but also to the human population. Therefore large-scale, incentive-based python derbys should be implemented in order to reduce invasive Burmese python populations with the intent of eliminating the population entirely.

The Burmese python had little issue with establishing themselves in the Everglades as a legitimate species. The warm habitat of the Everglades is an ideal place for the Burmese python to grow rapidly. The Burmese python is also an opportunistic hunter, and even though none of the Everglades’ native species are part of its original diet the small mammals were quickly found to be perfect prey. Another aspect that has allowed the python to thrive in the Everglades is their ability to swim (Harvey et al 2008). The Everglades are filled with channels and rivers that the pythons can easily navigate, allowing them to reach parts of the park which are not easily accessed by humans. Due to the fact that humans, and the occasional alligator, are the only predators pythons need to worry about, their ability to swim has been a main reason as to why they have grown so rapidly (U.S Fish and Wildlife Service, 2012). Another main reason is due to their reproductive cycle. The Burmese python has an average lifespan of 15-25 years, and they reproduce every year between December and April (Harvey et al., 2008). This, paired with the fact that the average clutch size is 36 eggs, one female python was even found with 85 eggs, gives insight to how the Burmese pythons have grown so rapidly since first being introduced as an exotic species (Harvey et al., 2008).

The introduction of these snakes into this environment has cause a quick decline in many important species of small mammals that previously called this environment home. The decline of population numbers of these key species due to burmese pythons has significant ramifications on the environment and overall balance of the ecosystem. Invasive Burmese pythons have caused small mammal populations to drop significantly. One study revealed that between 2003 and 2011 there was a 99.3% decrease in raccoon observations in areas where pythons settled, specifically the Everglades (Dorcas et al., 2012). One data model tested how significant the negative effects on raccoons are in parts of Florida, with a range from significantly affected to no effect. Raccoons in parts of the Everglades where pythons are well documented continually showed that their population is being significantly affected by pythons. Meanwhile, raccoons in urban environments fell on the other side of the range, demonstrating that the effect from pythons is not as significant in areas pythons frequent less (Reichert et al., 2017). This data shows the obvious negative impact these creatures have on the populations of animals normally found in this environment.
The decline of population numbers of these species may not seem significant to the average person but these declines leave long lasting effects on local ecosystems. These creatures pose a threat to species sending them closer to extinction. Remains of endangered bird species have been found in the digestive tracts of burmese pythons in the Everglades proving that these snakes are contributing to the decline of endangered species in this ecosystem (Hill, 2018). Burmese pythons have also been found to negatively affect rabbit populations in the Everglades. Marsh rabbits’ populations increased when closer to urban environments, where Burmese pythons are not as common, furthering the idea that Burmese pythons are causing the population decline (Reichert et al., 2017). A study done by the University of Florida specifically looked at how rabbit populations differed as the distance from urban environments decreased. This study used a scale of 0 to 1, with 0 being no rabbits in that area, and 1 being an abundant rabbit population. In the center of the Everglades, where pythons are most commonly seen, most locations scored 0 or close to 0. At 150 km from the center of the Everglades, near urban populations, the scores were much closer to 1, indicating larger rabbit populations (Sovie, McCleery, Fletcher, & Hart, 2016). These studies both conclude that rabbit populations have larger population declines in the everglades, where burmese pythons are common. Marsh rabbits play a role in keeping the ecosystem balanced and the removal of this important species may cause issues with food sources for other animals and sudden overpopulation of certain plants that are typically controlled by these rabbits.
Burmese python pose a significant threat because they have no direct predator in this environment and are capable of consuming most animals that cross their path, regardless of size (Hill, 2018). Being the top predator in this environment means there are no animals who are actively preying on these pythons, allowing for their populations to grow uncontrolled. The pythons ability to consume large animals have made the commonly found white-tailed deer a direct target. White-Tailed deer in the Everglades regions have experienced population declines of 85-100% due to the predation of pythons (Willson, 2017). Other mammals see similar declines, such as bobcats, opossums, and foxes. All three of these species fall into the 85-100% range of decline in population size in the Everglades, since Burmese pythons were first discovered in the Everglades (Willson, 2017). The lack of predators to control python populations and the rapid decline of crucial species population sizes spells disaster in the near future for this environment.

Burmese python populations are not only affecting the ecosystem but are also affecting the way infectious diseases are passed through mosquitoes causing significant threats to public health. This decrease in mammal populations had led to a shift in blood hosts for Culex erraticus, a mosquito species, from mammals to reservoir host. Reservoir hosts are animals, usually rodents, who carry pathogens that are harmful to other creatures, such as the eastern equine encephalitis virus, while not exhibiting any of the negative effects of the pathogen themselves. Cx erraticus is suspected to be a vector of the eastern equine encephalitis virus. There are a few theories as to how this rat avoided the effects of the Burmese python invasion. It could be that its predators were reduced by the python, or that they breed quick enough to avoid the effects of this new predator (Albeck-Ripka, 2017). A study conducted by the University of Florida looked into how significant this shift from mammals to reservoir hosts actually is. Feedings upon deer, raccoon and opossum in the Everglades decreased from 45.1% to just 0.8% of total hosts between the years 1979 and 2016 (Hoyer et al., 2017). This study found that the shift from mammals to reservoir hosts, mainly the hispid cotton rat, increased by a dramatic 422.2% (Hoyer et al., 2017). This shift would mean harmful pathogens, such as the eastern equine encephalitis virus, would spread more rapidly to mosquitos making the likelihood of transmission to humans more significant.
Burmese pythons are also a likely prey for Cx erraticus. One study collected 511 mosquitos from the Everglades region and tested their blood meals for DNA. Of the samples of blood meals collected, 78.4% contained blood from the Burmese pythons, while the majority of the rest of the sample contained human blood (Avery et al., 2018). These results from Avery et al. (2018) suggest that mosquitos in the Everglades have begun to see the Burmese python as another main source for blood meals, shifting away from their historic main source for blood meals of mammals. Another case study conducted at the University of Michigan found two adult Burmese pythons that previously consumed various species of reservoir hosts, which carry diseases acquired through infected mosquitoes. This is significant because pythons become infected by the species they have consumed. When mosquitoes feed on infected Burmese pythons they continue the transmission of infectious pathogens (Smith et al., 2007).

This data points to the conclusion that substantial shifts in mosquito blood meal hosts have occurred in the Everglades and these shifts correspond with the decline of medium and large-sized mammals due to the presence of an increased invasive Burmese python population. This shift towards reservoir hosts means an increase in the spread of potentially dangerous pathogens. Pythons are furthering this transmission by feeding on animals which carry diseases, becoming infected, and then being fed on by various mosquito species. This shift may begin to have an effect on human populations as these pathogens are being spread to us at an increased rate (Avery et al., 2017). More and more mosquitos are becoming infected with pathogens that can then be easily transmitted to us. If we want to protect ourselves from infected mosquitos the greatest solution would be to reduce Burmese pythons population in southern Florida in order to allow mammal populations that don’t carry pathogens to recover.

Invasive species’ derbys are effective at producing high catch rates of invasive species. It has been shown in the past that derbys that have been conducted have helped to significantly control the population of invasive species that are posing a problem in an environment. Volunteers participating in annual fishing ‘derbies’ for invasive Indo-Pacific lionfish in the Tropical Western Atlantic, an exotic predator which consumes a range of native species and now occupies millions of square miles of marine habitat, reduced lionfish numbers by 52% over a 192 km^2 area on average during single-day events from 2012 to 2014 (Green, Underwood, & Akins, 2017). We acknowledge pythons may be more difficult to find than lionfish. However, past derbys show that it is possible to find them. The Python Elimination Program created by the South Florida Water Management Department has eliminated 158 pythons in a little over two months (SFWMD, 2017). In February 2013 it was estimated that there are between 30,000 and 150,000 burmese pythons in the Everglades and southern Florida (Sarill, 2016). The overall impact seems small but this has been proven to be the most effective option in eliminating this invasive species. The state of Florida implemented the Florida Python Challenge in 2013 and the 1,600 competitors captured 68 snakes (Robinson, 2017). This may seem like a small amount compared to the population size of pythons in the everglades but it is important to keep in mind that these events are often short. If the events were made larger and more frequent catch rates would increase to a sustainable number.

Implementing derbies for the control of invasive Burmese Pythons in southern Florida is an effective way of reducing the population in a costly effective manner. These derbies, which have already been implemented in 2016 in Florida, work by charging a $25 fee to participate in the derby. Participants are challenged to catch as many pythons as possible and are rewarded for catching the most and biggest Pythons they can find. Over a thousand people, who travel from all across the country, participate in these derbies creating a surprisingly profitable operation, meaning money is actually being made from these operations instead of lost. In 2011 this python hunting industry was actually valued at $1.4 billion during an economic evaluation (Sweeney, 2016). These durbies are a creative way to financially and environmentally benefit from the reduction of invasive species populations. Conducting these derbies to control the population of these invasive pythons not only positively affects the environment that is invaded by these creatures but also positively effects the python hunting industry financially.

Through proper training, all volunteers will be aware of humane python killing practices. A drawback of recruiting amateur hunters is that many of them have little to no experience with the proper way to hunt the pythons, some even struggle to correctly identify the snake (Christy, 2013). The organizers of the Python Challenge attempt to fix this problem by requiring all participants to use their online training module, which is just a slideshow and does not include a test at the end. Furthermore, without hands on practice amateurs can not be expected to humanely kill the Burmese Python, which according to the Florida’s Fish and Wildlife Conservation Commission is to decapitate the snake, or to stab it in the brain at a specific angle so as the snake does not feel pain (Python Challenge, 2015). There is also in-person training, however this is only optional. This can be problematic as Florida is home to many snake species, some even resembling the Burmese Python. The Eastern Indigo Snake specifically is another large species of snake, which is a major issue as the Eastern Indigo Snake is a federally protected species (Christy, 2013). If the Python Derby is to be an effective derby, the participants will all need to go through the in-person training. With the in-person training the overall session takes up to two hours, as opposed to the online course, which can be completed in 10 minutes (Christy, 2013). The in-person training goes over everything on the online course, except in a classroom setting, and then afterwards the participants will get to handle alive Burmese Pythons (Python Challenge, 2015). If this training was required for all hunters instead of just the online slideshow, hunters would be more prepared with identifying the pythons, and knowing how to humanely kill them as they would have already had hands on experience. The Python Challenge organizers already suggest that participants make time for the hands on training, as they found that the most experienced hunters always came away with more pythons (Wesdock, 2015). Another issue that may cause problems is that the Everglades are a dangerous environment, and Burmese Pythons, while not venomous, can be a threat towards humans, especially when provoked. However, since the Burmese python was introduced to the Everglades there have been zero reports of any wild pythons attacking park visitors or even hunters participating in the Python Challenge(National Park Services, 2017). There are however other species of snakes which are venomous,such as the very dangerous Florida cottonmouth, and not to mention the threat of both the American alligator and American crocodile (National Park Services, 2017). A proper hands on training course would prove to most beneficial in educating the participants on how to navigate the Everglades, and avoid dangerous creatures. A hands on training would also give the amateur hunters the knowledge needed to track, and kill a much greater amount of pythons than seen in previous years.

Invasive Burmese pythons pose a threat to the environment of southern Florida, therefore large-scale, incentive-based python derbys should be implemented. The most notable effect documented has been the major decline of many native species, specifically raccoons and rabbits. With population declines of 85-100% in most areas where Burmese python populations are established it is clear that the pythons have negatively affected the Everglades since they were introduced (Willson, 2017). Recently scientists have also began to notice indirect effects from the pythons.Medium to large sized mammals, such as bobcats and foxes, have also seen decreases in population numbers suggesting that they are being outcompeted for prey by the Burmese pythons (Dorcas et al., 2012). Due to the fact the Burmese pythons have been directly linked to small population declines it can be deducted that they are linked with these trophic cascades as well. With the steep populations decline in many small mammals mosquitos have changed their blood meal targets to the Burmese python itself, and many rodent species (Hoyer et al., 2017; Avery et al., 2018). This is troubling as rodents often carry pathogens dangerous to humans, that are now becoming more common in mosquitos (Smith et al., 2007). This switch of blood meals for mosquitoes may become a real problem for people who live in communities in Southern Florida if mosquitoes continue to target rodents. With no natural predators in the Everglades, besides humans and occasionally an alligator, the Burmese pythons have easily established themselves and have caused a multitude of problems. Combating their now large population numbers appears to be a daunting task, but with a properly run python derby their population could lose numbers that may be too difficult to come back from. Derbies involving the lionfish have proved that these mass hunts can be an effective way to control growing populations (Green, Underwood, & Akins, 2017). Even small scale python derbies eliminated over a hundred pythons in two months (SFWMD, 2017). These derbies also prove to be cost effective, as they require a fee to join and only the best hunters receive large cash prizes (Sweeney, 2016). Finally, with hands on training on how to properly identify and euthanize the Burmese pythons amateur hunters should have no issue with killing native species or prolonging any snake’s death. These derbies have proven to be effective at killing Burmese pythons in the past. With more participants and a more hands on training course these derbies could be the most effective way at reducing Burmese python populations, and reversing the effects they have had on the environment of the Everglades.


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