Texas Parks & Wildlife Magazine   


Cold-Blooded Killers

From the diseases they bring to the ticks that hitch a ride on them, non-native reptiles and amphibians can wreak havoc on an ecosystem.

By Arturo Longoria

The human aversion to snakes, lizards and other scaly things has its roots in myths and legends, which often depict reptiles as tempters and connivers, and even great dragons born of evil and mischief. The fact that some reptiles are venomous has contributed over time to this innate dread. Still, with the exception of a handful of venomous snakes, most Texas reptiles are benign and serve as useful predators, balancing out rodent and insect populations and serving as allies in the overall harmony of nature.

However, sometimes things can go awry, especially when foreign species are introduced into areas where they interfere with endemic animal and plant life or when they carry pathogens that can decimate native or domestic animal populations. Obviously, reptiles are not the only introduced exotics that can disrupt ecosystems. Texas landowners are familiar with fire ants, Africanized bees and a slew of invasive grasses. Then there are the mammals, feral hogs and aoudad sheep, not to mention the sika and other exotic deer that have displaced many Hill Country and South Texas whitetails. Along with the unstoppable kudzu in the American Southeast and aquatic hyacinth clogging waterways like the Rio Grande, the casual or innocent transplantation of one species into the range of another often wreaks havoc on the biological status quo.

When it comes to introduced reptiles, and amphibians as well, Texans face the likelihood of two major problems. First, transplanted species can overwhelm native populations and push them out of their preferred habitats. Perhaps even more disturbing is the possibility that tenacious tropical pathogens might hitch a ride within the parasites that live on reptiles and amphibians, and thus spread diseases that have the potential to wipe out animals like white-tailed deer and domestic livestock.

Wildlife biologists and other researchers are always on the lookout for exotic reptiles and amphibians that have either been abandoned by their owners in refuges and sanctuaries, or were transported into backyards and city parks amid plants purchased at nurseries.

“We caught a tortoise not long ago that had some very interesting ticks attached to it,” says Mitch Sternberg, a wildlife biologist for U.S. Fish & Wildlife who works at the Lower Rio Grande Valley National Wildlife Refuge in South Texas. “Not long after we found the tortoise, we found a marine toad with more ticks that looked pretty rare.”

Sternberg said that several suspicious ticks were sent to scientists at the National Veterinary Services Lab in Ames, Iowa, which identified one as Amblyomma rotundatum. Also known as the rotund toad tick, this species was introduced from Africa and has been identified on the North American mainland only in South Florida and on Mexico’s Pacific Coast in the state of Guerrero. How the tick arrived in South Texas remains a mystery, but the event gives a whole new meaning to keeping our borders safe from unregulated entry.

“On the refuge we’ve found two iguanas, one about four feet long that shimmied up a tree, and an African spurred tortoise, and even one tortoise that had its shell painted purple, obviously by the owner who abandoned it,” says Sternberg.

Sternberg adds that while one parasitological expert has suggested that the previously unseen tick was perhaps misidentified, biologists are still concerned that a non-native animal could introduce a potentially devastating disease like heartwater into the country. Also known as cowdriosis, heartwater is a non-contagious disease endemic to Africa (but now known throughout the Caribbean) that is carried by ticks of the genus Amblyomma and is caused by a rickettsial organism known as Cowdria ruminantium. The effects of the disease can range from moderate to lethal. It could pose an acute threat to ruminants like cows, sheep, goats and deer.

“That’s precisely why the area along the Rio Grande from Brownsville to Laredo here is patrolled by tick riders [known officially as Mounted Patrol Inspectors for the Fever Tick Eradication Program]. We have a general quarantine for ticks so no one can transport a cow north across Highway 83 without first being tested for tick-caused infections,” says Roel Treviño of the Natural Resources Conservation Service.

Even so, biologists worry that cows wandering into the United States, or those that are purposely smuggled across the border, may not be the only ways that infected ticks travel to our mainland.

“Tick inspectors are watching out for cows and such,” Sternberg says, “but we also need to keep a lookout for reptiles and other animal species that probably go unnoticed and yet need to be monitored. Besides, it’s not just diseases we’re worried about. There is also the question of species competition. An introduced reptile can sometimes depose native reptiles.”

One of the best examples of reptilian niche displacement occurs in the American South, and possibly soon throughout Texas, where the Caribbean brown anole has successfully shoved our native green anole out of part of its preferred hunting territory. The brown anole (Anolis sagrei) first arrived in the Florida Keys in the late 1800s. But it wasn’t until the early 1960s that biologists observed that this member of the anole family, which includes some 300 species worldwide, had begun to oust the green anole (Anolis carolinensis), which is our only native anole and was first observed by Europeans in the mid-1600s. The displacement, however, was not of the kind where one animal moves into another’s territory and pushes it clean out.

At my McAllen home, I recently spotted a brown anole (the first I’d ever seen) perched on our cedar fence. That’s when I first called Mitch Sternberg, who gave me the lowdown on how this lizard native to the Bahamas and Cuba had arrived in South Texas. I also noticed that the brown anole never foraged into the higher branches of my front yard’s mesquites and ebonies, and likewise stayed clear of the higher limbs of my brasil trees where we usually spot all our local green anoles. Green anoles prefer to hunt from “ground to crown,” meaning that they look for insects from along the ground all the way up to the crown of trees. The brown anole, on the other hand, prefers to hunt from “ground to trunk,” meaning that it stalks insects only from ground level to no more than about five or six feet off the ground.

“In Florida the green anole seems to be on the decline,” Sternberg says. “Studies have shown that when the brown anole gets established it will drive the green anoles off the ground and lower trunk areas and into the higher branches that occupy the tree’s crown.”

Might this make the green anoles more likely to be spotted by predatory birds or remove it from some of its preferred food sources? Well, scientists don’t seem ready to render any sort of definitive conclusions in that regard. But the fact that brown anoles can muster the muscle and tenacity to push green anoles into the upper tree crown has many biologists concerned.

“The bottom line is that in areas where the brown anole becomes prevalent we see a decline in green anoles,” says Sternberg.

In places like Guam, the introduced brown tree snake has greatly diminished native bird and lizard populations. An accidental or intentional release of a reptile species not known to Texas might create the same sort of ecological disaster here.

Still, all the news isn’t quite so apocalyptic. Shannon Ferrell, a clinical veterinarian who works as a researcher and practitioner at the Fort Worth Zoo, maintains that despite the potential for problems, there are active measures in place to protect the unwanted introduction of exotic reptiles and amphibians and the diseases they may harbor.

“Under USDA regulations, most incoming animals to the U.S. have to undergo extensive diagnostic testing and possible quarantine in both their country of origin and at designated USDA import sites to detect diseases such as Cowdria ruminantium,” Ferrell says. Places like the Fort Worth Zoo quarantine incoming animals for 30 to 90 days more in order to watch for infectious diseases and remove parasites.

“If a concerning parasite or disease enters Texas, the state or federal authorities alert the veterinary medical community and render instructions for possible containment measures,” Ferrell says. He cautions, though, that “this type of drastic occurrence would be rare in our area [Dallas/Fort Worth], but could be more foreseeable in the border regions with Mexico.”

Officials are also on the lookout for Coxiella burnetii, known as Q-fever, another organism transmitted by ticks, says Ferrell. Again, Ferrell emphasized that the probability of foreign reptiles introducing diseases into the state that might affect mammalian livestock is remote. However, the possibility of diseases from exotic reptiles infecting native reptiles is another matter.

“The imported herpetofauna usually have no clinical disease and often carry their infectious organisms in low numbers. But releasing foreign reptiles into our ecosystems would create the opportunity for these infectious agents to find new and [susceptible] reptilian hosts that most likely would result in severe and widespread fatal infections within a suitable reptile order,” Ferrell says.

Ferrell has firm opinions about the ownership and abandonment of reptiles into the wilds. “My recommendation is preventative,” Ferrell says. “Do not own exotic reptiles. The trade in exotic reptiles is partially responsible for reptile depopulations in their countries of origin, the introduction of foreign parasites and diseases to the United States, competition and displacement of native North American herpetofauna, and potential damage to other native fauna populations through predation.”

Or to put it another way, if you want to see something exotic, take a trip — and don’t bring anything home.

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