Iguanas are remarkable lizards with a bizarre ability to seemingly ‘come back to life’ after freezing stiff. If you’ve seen videos circulating online of frozen iguanas thawing out and scrambling away, you may be wondering – is this real? Can iguanas actually freeze solid and survive?
If you’re short on time, here’s the quick answer: Yes, some iguanas have the unique ability to freeze their bodies while still alive, entering a dormant frozen state. When temperatures warm back up, the frozen iguanas can thaw and ‘come back to life’, waking up and moving around again.
In this nearly 3,000 word guide, we’ll cover everything you need to know about this strange cold-weather survival skill that certain iguana species possess. You’ll learn the science behind how and why they freeze, what their frozen bodies look like, how they thaw out and recover, if freezing harms them, where these cold-resistant creatures live, and much more.
The Biology Behind Freezing Iguanas
Differences Between Iguana Species
There are numerous iguana species found in the tropics, but the ones that occasionally freeze in parts of North America are the common green iguana (Iguana iguana) and the spiny-tailed iguana (Ctenosaura similis).
Both species originated in Central and South America with a small native range extending into Mexico and southern Florida. However, due to the exotic pet trade and accidental or intentional releases of captive specimens, some iguana populations have become invasive in Puerto Rico, Hawaii, and southern parts of the mainland U.S. Green iguanas seem to tolerate cold better than their spiny-tailed cousins.
Entering a Frozen State Called Cold Stunning
When temperatures fall below 50°F (10°C), an iguana’s body will start to shut down as cold-blooded animals cannot produce enough internal body heat. This is called “cold stunning,” where the iguana becomes very sluggish, stops moving, and appears dead. Their heart rate and breathing slow tremendously but do not fully stop.
If cold conditions persist for over 8 hours, ice crystals can begin to form inside cells causing tissue damage.
Physiological Changes Protect Vital Organs
An iguana’s body undergoes changes to protect vital organs when cold stunned. Glucose gets released to supply the brain with energy reserves. Blood and bodily fluids become more viscous to reduce leakage from cells.
The cloacal bursae, two bags of tissue near the tail, draw water away from other tissues to prevent ice crystal formation. Without these crucial physiological responses, the iguana would die much more rapidly when frozen.
Thawing Out and Coming Back to Life
Provided an iguana has only been frozen for a short period, it can thaw out and recover when ambient temperatures rise again into tolerable conditions. The heart rate kicks back up circulating thawed blood, breathing resumes, muscles limber up, and normal activity returns once the body regains sufficient warmth from basking.
Severely frozen iguanas may display permanent organ damage, occasionally resulting in death post-thaw. Otherwise healthy individuals can withstand and bounce back from temperatures below freezing quite extraordinarily!
Myths vs Facts About Frozen Iguanas
Myth: They’re Dead When Frozen
A common misunderstanding is that iguanas are deceased when they appear frozen stiff in cold weather. While they may look lifeless, frozen iguanas are not dead at all. Their bodies enter a hibernation-like state that lowers their biological functions to survive the cold.
Fact: They Enter a Hibernation-Like State
When temperatures drop below 50 degrees Fahrenheit, iguanas go into a frozen mode called “cold stunning.” Their heartbeat and metabolism slow dramatically so their bodies can endure the frigid conditions. Their muscles and other tissues are preserved by the cold.
So while frozen iguanas appear dead, they are actually in a type of suspended animation.
Myth: They Freeze from the Inside Out
It’s a common misconception that iguanas freeze from the inside first. In fact, the initial freezing happens in the spaces between the iguana’s cells before the cells themselves crystallize. Intracellular fluids do not start to freeze until slightly colder temperatures.
Fact: Ice Forms in Spaces Between Cells First
When iguanas get cold enough, ice crystals first form in the spaces between their cells, in a process called supercooling. Water moves out of the cells and into these intercellular spaces where it solidifies into ice.
This helps protect the cell membranes and organelles from damage during the early stages of freezing.
Myth: They Always Survive Freezing
While iguanas are well adapted to freezing temperatures, extreme cold brings risks. Young, old, or sick iguanas are most vulnerable. Prolonged freezing can still damage cells and tissues. And frozen iguanas are helpless, leaving them prone to predators and cars.
Fact: Extreme Cold Poses Risks
According to Florida Fish & Wildlife, large numbers of iguanas die in exceptionally cold weather when temperatures drop below 40°F for longer than 8 hours. Dangerously chilled iguanas can experience physical damage, organ failure, and loss of limbs from frostbite.
Young and small iguanas are at highest risk of perishing in freezing weather.
Where Cold-Resistant Iguanas Live
Native to Tropical Climates
Iguanas are reptiles that originally evolved in the warm, tropical areas of Mexico, Central and South America, and the Caribbean islands. The green iguana (Iguana iguana) and spiny-tailed iguana (Ctenosaura similis) are two common species that thrive in hot environments with temperatures between 77-95°F.
Iguanas are cold-blooded, so their body temperature depends on external heat sources like the sun. In their native habitats, iguanas have abundant vegetation and access to direct sunlight practically year-round.
Invasive Green Iguanas in Southern U.S.
Non-native green iguanas were introduced to South Florida through the exotic pet trade beginning in the 1960s. They have spread significantly across southern Florida due to the warm, humid climate. Iguanas can also be found along the Gulf Coast in Alabama, Louisiana, Texas, and parts of California.
Green iguanas are considered an invasive species in these areas. They cause damage to infrastructure, compete with native wildlife, and can transmit salmonella.
Green iguanas can survive dips into the 50s°F in their expanded territories, but prolonged exposure to temperatures below 45°F can be dangerous. Their metabolism and bodily functions begin to shut down in cold weather.
| Winter Temperatures | South Florida | Central Florida |
|---|---|---|
| Average High | 73°F | 65°F |
| Average Low | 57°F | 48°F |
Preparing for Cold Snaps
When forecasts predict cold fronts or freezes in southern states, it’s not uncommon for iguanas to fall out of trees in a comatose state. But they aren’t necessarily dead. Iguanas have the ability to slow down their physiological functions and metabolism to survive cold stress.
In cold weather, iguanas go into a hibernation-like state called brumation. Their heartbeat and respiration slow dramatically, allowing them to conserve energy. But if temperatures drop too low for too long, iguanas can suffer from frostbitten toes and tail damage. Severe cold can also lead to death.
Zoos with iguana exhibits often bring sensitive reptiles indoors when cold snaps occur. Green iguanas in the wild don’t have that luxury, but they can burrow into dirt or hide under thick vegetation to insulate themselves from freezing temperatures.
They tend to live close to large bodies of water, which also help stabilize cold weather impacts.
Dangers of Freezing for Iguanas
Injuries and Health Issues Upon Thawing
When iguanas freeze, their bodily functions slow dramatically but do not completely stop. So when they thaw, injuries and health issues can occur (source). Lizard scientists (herpetologists) have found the following common injuries after thawing:
- Frostbite on toes, tail, and spines – This can lead to tissue damage and even loss of digits or the tail.
- Blindness – Freezing can damage the retinas.
- Infections – Bacteria like Aeromonas hydrophila can enter wounds and cause infections.
- Pneumonia – Fluid can build up in the lungs during freezing.
- Death – If freezing lasts too long or thawing happens too fast, it can kill them.
The stress of freezing can also suppress their immune systems after thawing, making illness more likely. Dehydration and intestinal damage are also common consequences. 😧 In all, freezing is pretty dangerous for these cold-blooded critters!
The injuries may heal over time, but can impact their health and ability to thrive. 🦎
Predation Risks When Immobilized
When iguanas are frozen stiff, they cannot move or escape from predators like they normally would. So they are vulnerable to attack during the immobilized state. Predators like birds, snakes, crabs, raccoons, and even dogs may try to eat them or injure them while frozen.
One study found over 50% of frozen green iguanas had minor to major injuries from predators. Yikes! 😱
Even a quick nip or scratch could become seriously infected. Having to regrow a lost tail also drains precious energy from an iguana’s recovery. Being unable to flee for safety really puts these spiky reptiles in danger! Hopefully, they thaw and scurry off before becoming someone’s dinner. 🏃♂️
Long-Term Impact on Reproduction
Freezing cold temperatures can do long-term damage to iguanas’ reproductive systems. Studies have found freezing reduces sperm production in male iguanas and affects hormones involved in reproduction (source). It can also damage ovaries in females.
| Average # of Eggs Laid | Iguanas That Froze | Iguanas That Didn’t Freeze |
| 1st Year After Freezing | 18 eggs | 41 eggs |
| 2nd Year After Freezing | 12 eggs | 38 eggs |
As seen above, egg production drops significantly for iguanas that froze compared to those that didn’t. Their reproduction may rebound but often remains lower long-term. Since iguanas in cold climates freeze yearly, this can really impact populations over time. No fun for these frozen reptiles! 🥶
Frozen Iguana FAQs
What Does a Frozen Iguana Look Like?
When temperatures drop below 45°F, iguanas enter a frozen, comatose state. Their bodies become lifeless and rigid as they lose their ability to move. Their skin often appears pale gray or blue, and ice crystals form on their body, especially around the head and tail.
They may appear dead, but they are still alive in this frozen state. It’s an amazing adaptation that helps them survive cold snaps that aren’t typical in their tropical environment.
How Long Can They Stay Frozen?
Iguanas can remain frozen for up to 24 hours before thawing out. The cold-blooded reptiles can tolerate freezing temperatures for a day or more before they may start to suffer adverse effects. Their bodies enter a protective state that conserves energy and body heat.
However, if they stay frozen for too long, they risk developing frostbitten digits or tail tips over time.
Do Frozen Iguanas Feel Anything?
Frozen iguanas are completely unconscious and unaware of anything going on around them. They don’t feel pain or have any senses when in this comatose state. It functions as a protective mechanism that essentially puts the iguana into a temporary state of suspended animation until temperatures warm up again.
They are immobilized and totally numb during this time, which prevents damage to their cells and organs.
Why Don’t Their Eyes Freeze?
Iguanas have a protective membrane that shields their eyes while frozen. This transparent scale called the brille prevents their eyeballs from freezing. As cold-blooded animals, iguanas can’t regulate their own body temperature and have adapted mechanisms like the brille to prevent tissue damage when their bodies grow extremely cold.
Their eyes remain safe and intact beneath this protective coating.
Conclusion
As we’ve explored, some lizards have evolved the remarkable ability to freeze nearly solid in cold temperatures, entering a reversible dormant state to survive. While freezing offers an ingenious survival strategy when cold threatens otherwise tropical-dwelling iguanas, it is not without risks.
The bizarre phenomenon of stiff frozen iguanas seeming to ‘come back to life’ will continue to fascinate those who witness nature’s ingenuity. Hopefully this guide has shed light on the science behind their impressive cold resistance, and cleared up some common myths.
