Spotted lanternfly. Photo by J. F. Orth, FLickr
(To listen to an audio version of this blog, please click on the following link ….. Pythons, mosquitoes and leeches
I have written about invasive species many times before. I have done blogs about invasive insects like gypsy moths, Asian tiger mosquitoes, brown-marmorated stink bugs, spotted lanternflies and Asian lady beetles. I have done blogs about invasive birds like house sparrows and European starlings. I have also written extensively about exotic, invasive plants both back in Pennsylvania (where they have increasingly come to dominated our woodland trails, roadside ditches and old fields) and here in Colorado (where our “natural” grasslands now contain almost 30% invasive species and our riparian woodlands are increasingly overwhelmed by exotic species like Russian olive).
I even did a blog about the exotic, invasive species that was described in a New York Times article as “the most dangerous and destructive exotic, invasive species affecting our aquatic ecosystems today.” This deadly beast was, quite surprisingly, the common goldfish (Carassius auratus) ( see Signs of Fall 7, October 20, 2016). The impact of the rapidly growing and even more rapidly reproducing goldfish on natural freshwater streams, pond and lakes, though, is devastating!
In the goldfish blog (entitled “The Anthropocene R Us” (one of my best titles ever!)) I listed some other more obviously damaging exotic, invasive species that were affecting aquatic and semi-aquatic ecosystems all across North America. One of these species gets a lot of press coverage in part because of a widespread bias and fear that is shared by many humans (some say that it is a fear that s written into our primate DNA), and also because of its charismatic presence and almost supernaturally, monstrously, large size. This is species, of course, the Burmese python (Python bivittatus).
Photo by NPS, Public Domain
Burmese pythons were very popular pets in the last decade of the 20th Century and the first decade of the 21st. Between 1996 and 2006 over 90,000 Burmese pythons were imported into the United States as part of this pet trade. Breeding centers for Burmese pythons were also established primarily in warm, tropical to semi-tropical areas of the United States in order to satisfy the demand for these very large snakes (they can reach lengths of 23 feet and can weigh up to 200 pounds!).
One of these breeding centers, in Florida, was destroyed by Hurricane Andrew in 1992 and an unknown number of pythons escaped into the wilds of the Everglades and began to feed (they are stealthy, ambush predators that often hide in shallow water and strike and constrict their prey when they come to the water’s edge to drink) and breed (a Burmese python nest typically contains between 50 and 100 eggs). Pretty soon there were A LOT of gigantic, Burmese pythons in the woods and wetlands of south Florida.
The impact of these invasive snakes on the biotic communities of the South Florida ecosystems has been severe. They have eaten large numbers of birds, mammals and other reptiles. They consume anything from small song birds to adult deer and alligators! A 2012 report on the wildlife of the southern regions of Everglades National Park indicated that since 1997 racoon populations have declined 99.3%, opossum populations have declined 98.9%, white-tailed deer populations have declined 94.6%, bobcats have declined 82.5%, and marsh rabbits, cottontails, and foxes have been completely wiped out.
Burmese python nest, Photo by NPS, Public Domain
Recently, though, a team of ecologists from the U. S. Geological Survey, the National Park Service and the University of Florida made some hopeful observations on a possible example of biological control of Burmese pythons. Using motion sensitive cameras positioned around a python’s nest in the Big Cypress National Preserve in Florida, the scientists watched a 20 pound bobcat repeatedly visit the nest while the female python was away and eat 42 of the eggs in the python’s clutch. The bobcat also damaged (rendering them inviable) 22 other eggs in the nest! After several successful nest visits, the bobcat then encountered the female python and quickly departed only to return later to have a direct interaction with the 115 pound snake. The python lunged at the bobcat (and missed) and the bobcat struck at the snake’s head with his claws (and also missed).
This python/bobcat encounter was described in a February 19, 2022 article in the journal, Ecology and Evolution.
Amazingly, these huge Burmese pythons are very difficult to find in the field. They have excellent camouflaging coloration and tend to remain quite motionless as they wait, concealed in murky water or in thick vegetation, for potential prey to come within their strike ranges. One very common, natural resident of the Everglades, though, can quite easily find these large snakes and can use them as a food source to drive their reproductive biology. Anyone who has ever been to the Everglades is very familiar with the abundance and aggressiveness of these blood seeking creatures: mosquitoes!
Using simple mosquito funnel traps ,entomologists can collect samples of mosquito populations across very broad areas. Female mosquitoes after taking a blood meal, retain that blood in their digestive tracts for a significant amount of time, and this blood can be analyzed for the presence of python DNA. If this DNA is detected, then, there must be a python within the hunting area of those mosquitoes and snake hunters can go out with a significant edge in their search for these invasive reptiles!
Previously, we have talked about “environmental DNA” (“eDNA”). This is DNA from plants, animals and fungi that has been shed from the body of one of these organisms and is then present in water, air or on some environmental surface (see Signs of Spring 3, March 24, 2022). The eDNA that is accumulated in, and then recovered from some blood feeding invertebrate is referred to as “invertebrate DNA” or, iDNA). This type of DNA is not only useful in hunting for Burmese pythons, but it is may also be used to answer much more complex, ecological questions.
Tiger leech. Photo by D. Culbert, Wikimedia Commons
In the March 23, 2022 issue of Nature Communications, a group of scientists from the Kunming Institute of Zoology teamed up with park rangers in China’s Ailaoshan Nature Reserve and collected leeches throughout the reserve. Over the three month sampling period, 30,468 leeches were collected. The blood inside the collected leeches was sampled for iDNA, and a total of 86 different animal species were identified. These species ranged from domestic livestock (cattle, sheep and goats), humans, Asiatic brown bears and endangered, Yunnan spiny frogs!
Analysis of the abundance and distribution of this iDNA enabled the Kunming Institute scientists to construct models of animal distribution, movement and interactions throughout the reserve. Of particular note was the observed antagonism between both livestock and humans and wild species. Any area that was used for livestock grazing or frequented by people, had very low numbers and diversities of wild animals.
The low cost of this type of collection system and its ease of application coupled with the richness and detail of the data generated, makes iDNA sampling a valuable tool in both the detection of feral, exotic species and also in the study of native, wild animal populations!