Iguanas may be growing more tolerant to the cold, and that’s bad news for Florida

FORT LAUDERDALE, Fla. — When temperatures drop, so do green iguanas — from the trees. But evolution, it seems, could be robbing South Floridians of a tradition as common as checking the heat index on New Year’s Day.

Research shows that in recent years, several species of lizards have grown more tolerant of cold temperatures. It’s a discovery with big implications for Florida, where bouts of cool weather keep invasive iguanas contained to the southern regions of the state and helps keep populations under control.

It also could mean fewer images on social media and TV news of iguanas lying on their backs under trees, legs in the air, stunned until the warm sunshine gets their bodies moving again.

As recently as four years ago, most of South Florida’s most common species of lizards could tolerate temperatures between 46 and 52 degrees. Now, they hold up in temperatures as low as 44 degrees, according to a study done by a researcher at Washington University in St. Louis.

That means it’s possible that iguanas could expand their territory beyond their normal stomping grounds of Miami-Dade, Broward and Palm Beach counties.

“The potential is they could spread farther and disperse farther, so that’s why it’s interesting to Florida, specifically” said James Stroud, the research associate who conducted the study and did his doctoral work at Florida International University.

That’s bad news considering iguanas are invasive, propagate profusely and wreak havoc on homes, gardens, sidewalks, pool decks, seawalls, boats and anywhere else they eat and, well, poop. They’re so destructive, the state of Florida issued a call for homeowners to kill them. (It later clarified the statement, saying it’s best to call a professional to do the deed.)

Iguanas fall out of trees during cool weather because they’re cold-blooded and tropical. Low temperatures cause them to become sluggish and, in some cases, immobile. If it happens while they’re sleeping in trees, they often fall to the ground. They’re cold-stunned, not usually dead — they spring back into action once temperatures warm again if the fall from the tree doesn’t kill them.

It happened this past January, raining iguanas when temperatures in parts of South Florida fell to 39 degrees, the coldest air in about a decade. It also happened in January of 2018.

Stroud and his colleagues studied six lizard species common in South Florida — one that’s native (the American green anole), three Caribbean lizards that are not native (one each from Puerto Rico, Cuba and Hispaniola), the northeast tropical gecko, and the brown basilisk lizard.

Iguanas weren’t included because they were too big to fit into the refrigerator-like device used to study the chilled lizards. But Stroud said he believes the results apply to iguanas, too.

Blake Wilkins, co-owner of Hollywood-based Redline Iguana Removal, said the discovery doesn’t surprise him. While collecting iguanas during last January’s cold spell, he saw signs that iguanas might be warming up to the cold.

“I noticed a lot of them were actually in

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Man almost dies from an allergic reaction to cold air

Stepping out of a hot shower into a cold bathroom almost killed a Colorado man, who had developed a serious allergic reaction to cold temperatures.

a close up of a toy: Person wearing a mitten adjusting a radiator thermostat.

© Provided by Live Science
Person wearing a mitten adjusting a radiator thermostat.

The 34-year-old old man collapsed after getting out of the shower, and his family found him on the floor, according to a report of the case published Oct. 27 in The Journal of Emergency Medicine. The man was struggling to breathe and his skin was covered in hives. He was experiencing a life-threatening, whole-body allergic reaction known as anaphylaxis.

When paramedics arrived, his family told them that the man had a history of being “allergic to the cold weather,” according to the report. He had previously experienced hives as a reaction to the cold, but not anaphylaxis. These episodes started after he moved from Micronesia, which has a tropical climate, to Colorado, which sees colder temperatures, the report said.

Related: The 9 weirdest allergies 

Paramedics treated the man with epinephrine and oxygen, and rushed him to the emergency room. When he got to the hospital, he was sweating profusely and had hives all over his body.

Doctors diagnosed him with cold urticaria, an allergic reaction of the skin after exposure to cold temperatures, including cold air or cold water, according to the Mayo Clinic. People can also develop symptoms after consuming cold food or drinks, Live Science previously reported.

The most common symptom is a red, itchy rash (hives) after exposure to the cold; but in more serious cases, people can develop anaphylaxis, which can cause their blood pressure to plummet and airways to narrow, making breathing difficult. These more severe reactions typically occur with full-body skin exposure to the cold, such as when people swim in cold water, the Mayo Clinic says. In the man’s case, his entire body was exposed to cold air after stepping out of his shower. 

Gallery: Glassified brain cells found in victim of Vesuvius eruption (Live Science)

Doctor’s confirmed the man’s diagnosis using an “ice cube test,” which involves placing an ice cube on the skin for about 5 minutes. If the patient develops a raised, red bump on the skin where the ice cube was, they are diagnosed with cold urticaria.

Exactly how common the condition is overall is not known — one study in Europe found a prevalence of 0.05%, according to the National Institutes of Health. Anaphylactic reactions are less common than hive-like reactions.

In most cases, the cause of the condition is not known, but sometimes it can be inherited, meaning people have a genetic predisposition. In other people, cold urticaria is triggered by something that affects the immune system, such as a viral infection or certain cancers.

The allergic reaction happens because exposure to the cold causes the immune system to release chemicals called histamines, which trigger an inflammatory response, Live Science previously reported.

At the hospital, the man was treated with antihistamine and steroids, and his condition improved. Before he

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Cold temperatures, vitamin A can help the body burn more fat, study shows

People looking to lose weight may start embracing the winter months after a new study found cold temperatures and increased vitamin A encourage fat burning.

The study, which was published in the journal Molecular Metabolism last week, explored the effects cold temperatures and vitamin A had on converting white fat, which is where excess calories are stored, to brown fat, which “stimulates fat burning and heat generation.”

More than 90% of the human body’s fat deposits are white fat, which is stored in the abdomen, bottom and upper thighs, the study shares.

Cold temperatures applied to mice was found to increase vitamin A production, which resulted in higher fat burning. 

Cold temperatures applied to mice was found to increase vitamin A production, which resulted in higher fat burning. 


According to the findings, cold temperatures increased vitamin A levels, which helps convert white to brown fat, thus stimulating fat burning. Vitamin A reserves are mostly stored in the liver. Once cold was applied to the mice in the study, the increases in “the levels of vitamin A and its blood transporter, retinol-binding protein” led to a higher rate of fat burning as the white fat converted to brown as the body attempting to keep itself warm.

Alternatively, when “the vitamin A transporter ‘retinol-binding protein’” was blocked in mice, the fat did not “brown” and the mice were unable to protect themselves from the cold.


The study is promising in finding solutions to dealing with weight gain and obesity. Though the study’s lead researcher, Florian Kiefer from the Medical University of Vienna, cautioned against taking large quantities of vitamin A supplements in an effort to lose weight.


“Our results show that vitamin A plays an important role in the function of adipose tissue and affects global energy metabolism. However, this is not an argument for consuming large amounts of vitamin A supplements if not prescribed, because it is critical that vitamin A is transported to the right cells at the right time,” explains the MedUni Vienna researcher. “We have discovered a new mechanism by which vitamin A regulates lipid combustion and heat generation in cold conditions. This could help us to develop new therapeutic interventions that exploit this specific mechanism.”

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Florida’s falling lizards are getting used to cold winter temperatures

The lowest temperatures in a decade stunned and immobilized the lizards, causing them to lose their grip from their usually safe perches in trees.

Comatose lizards littering the sidewalk might have been annoying for residents. For scientists, however, it was a unique opportunity to understand how the lizards, many of which aren’t native to the region, are affected by extreme climate events. It turns out these reptiles are more adaptable to extreme temperatures than the researchers had thought, they said.

“When air temperatures drop below a critical limit, lizards lose the ability to move. Most commonly, the lowest daily temperatures occur at night while many diurnal (day-active) lizards are asleep,” lead study author and biologist James Stroud, a postdoctoral research associate at Washington University in St. Louis, told CNN.

“As many diurnal lizards typically sleep above the ground, perched safely in and among leaves and branches, they may lose their grip if temperatures drop below this critical functioning limit.”

The January cold snap wasn’t the first time Floridians have faced lizards dropping out of trees. It can happen anytime the temperature gets below 45 degrees Fahrenheit.

Stroud and his collaborators in late January and early February collected 63 lizards from six different species around Miami, five of which were tropical species and not native to southern Florida.

The researchers took the lizards back to the lab at the University of Miami and individually cooled the animals until each one was too cold to respond to a gentle prod on its back limb.

“At this point, the lizard was removed from the cooler and the internal body temperature of the lizard was recorded as its lower temperature limit,” Stroud said.

“Lizards were then allowed to return to room temperature; every single lizard in this study recovered back to full health after just a few minutes.”

The team repeated this 10 weeks later to rule out a very quick, individual-level response.

National Weather Service warns of falling iguanas

The scientists were then able to compare the temperatures to earlier data they had gathered in 2016 for a study that forecasted how far north the non-native lizards could potentially disperse to from where they were first introduced in Miami, south Florida.

The lizard community, the researchers discovered, had responded in an unexpected way to the cold snap: All of them could withstand cold temperatures down to about 42 degrees Fahrenheit, regardless of their previous ability to tolerate cold.

Central American brown basilisks (Basiliscus vittatus) are among the members of a lizard community that converged on a lower temperature tolerance after a cold snap in Miami.

“A major unexpected result of this study was that all species converged on the same new, lower level of thermal tolerance,” Stroud said.

“While there was great variation in temperature tolerance before the cold event — some, like the large-bodied brown basilisk, were very intolerant of low temperatures, while others like the Puerto Rican crested anole were more robust — we observed that all species could now tolerate, on average, the same lowest temperature.”

Stroud said from this study, which published Tuesday in the journal Biology Letters, it wasn’t clear whether the lizards were adapting to the lower temperatures in a way

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