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Florida's tegu lizards are migrating north. Here's what this invasion means for the state's wildlife

Close-up of a tegu in a cage.
The Florida Fish and Wildlife Conservation Commission
According to Florida wildlife officials, invasive Argentine black and white tegus are large lizards that can reach nearly five feet in length, and they have a mottled black and white coloration that often is arranged into a banding pattern across the back and tail.

Tegus have been reported in 35 Florida counties, including nearly every part of the greater Tampa Bay region. A new factsheet shows their presence is now established in several North Florida counties and as far north as Georgia.

A new paper co-authored by the University of Florida and partner agencies details the invasion of Argentine black and white tegu lizards in the state of Florida over the past decade. It looks at signs of the population’s increase, wildlife impacts, and efforts to reduce the threat.

Click here to view the factsheet

The invasive species are known to eat the eggs of important animals in Florida, like American alligators and rare birds, which are biological indicators for Everglades restoration.

Tegus have been reported in 35 Florida counties, including nearly every part of the greater Tampa Bay region. Their presence, measured mostly by the number of tegus trapped and removed, is now established in several North Florida counties and as far north as Georgia.

Color-coated map of tegu populations in each Florida county.
EDDMapS; Accessed 20 March 2020
This map depicts the number of verified Argentine black and white tegu reports through March 2020. Hillsborough, Charlotte, Miami-Dade, and St. Lucie Counties have established breeding populations.

Melissa Miller, who oversees invasive species research at UF's "Croc Docs" Laboratory in Fort Lauderdale, explains how these massive reptiles from South America are adjusting to a northern migration.

What do we know of the tegu population now?

We know that their population has been increasing. In the factsheet, there's a figure that shows the combined number removed by all the different organizations, agencies. And we see a pretty marked increase up until 2019. There's a big spike, particularly for that year, and we know that they have the ability to expand pretty far north in Florida. And especially with the knowledge that there's an established population in Georgia, we know that they're able to overwinter in Florida.

So, if they can live through freezes, and are now found in four Georgia counties, do we have any reason to believe that they can head even further north?

Well, they'll go down into burrows, so they'll escape that extreme cold … they'll kind of like down-regulate their body where they're not using much energy at all. And that helps them to get through the cold winter months and not require them to really come out and eat much or anything. So, I would say it is probably likely they could survive further north.

Are you trying to forecast where they will likely spread next?

Yeah, so USGS is working with some folks up in Georgia to look at that population. In Florida, one of the difficult things with invasive species is kind of figuring out: OK, so if you get a tegu in the panhandle, is that just someone's pet that got loose or they released, or is that coming from whatever the most nearby population is?

Can you describe all the ways in which tegus are being combated?

So, the live-tracking, multiple partners are engaged in that. The camera surveillance to detect where they're at and where to prioritize efforts and assess the feasibility of removal in different areas. And then there's the radio telemetry to understand their behaviors and movements in habitat use. And FWC (the Florida Fish and Wildlife Conservation Commission) actually hires contractors to set traps and remove tegus.

And they also run a trap loan program for the public. If someone calls and says they have a tegu in their yard, they loan them a trap, and help them with catching the tegu, and then they'll come and get it. There's an 888-IVE-GOT1 hotline, and that's for reporting tegu sightings. So once someone reports a tegu sighting, then we kind of work together to see who's closest, depending on where the tegu spot is, so they can go respond to that.

And, of course, you know, the federal and state agencies support a lot of like research, and it all kind of works in tandem to try to achieve the larger goal of containment for tegus. Because if we fail at containing tegus, then the next step is long-term management and just resource protection. And that's very costly and often ineffective, and that's where we are with pythons right now, for example. So, we want to try to do as much as we can with tegus right now, to prevent more impacts to wildlife, more impacts to Everglades restoration, and to prevent their spread in general.

And is there any indication that these efforts are working?

Yeah, there are. We're catching fewer tegus. Since 2019, as you see in the figure in the factsheet, the numbers were going up. And then since 2019, we're starting to see a reduction in the number of tegus that we've captured. And the amount of time given the same number of traps we have out, we're actually spending the same amount of time getting fewer tegus, indicating that they're less abundant in that area.

Since 2012, I’ve been a voice on public radio stations across Florida - in Miami, Fort Myers, and now Tampa.