Melissa Kaplan's
Herp Care Collection
Last updated January 1, 2014

Hypothermia in Iguanas and Other Reptiles

©2000 Melissa Kaplan

Iguanas, like many reptiles, have two strikes against them when it comes to hypothermia.

First, they are reptiles: they do not produce their own body heat, so when external heat sources are absent, their body cools down. Larger reptiles take longer to heat up, but also longer to lose body heat, so small iguanas will become hypothermic faster than large ones. Second, because they are a tropical species, they require higher temperatures than temperate climate reptiles and, since their bodies are not adapted to hibernation, they are unable to deal with low temperatures. Iguanas who get away outside during cool or cold weather, escape from their indoor enclosure or hide during seasons when the temperatures inside the house are cool or cold, may become hypothermic.

What Is Hypothermia?
In mammals and birds, the body tries to make heat by shivering, and then conserves heat to support internal organs as long as possible by withdrawing the blood supply from the extremities. Reptiles lose heat when faced with temperatures dropping lower than the temperatures at the low end of the species required thermal gradient. Since they are ectotherms, they do not manufacture their own body heat, so will not be able to stay as warm as a mammal or bird subjected to a cold environment. (Female pythons who are incubating eggs "shiver" during incubation apparently as a way to increase body temperature to aid in the incubation of their eggs, but they do not seem to do this when they are kept too cold, or the temperatures drop too rapidly for the shivering to offset the overall loss in body temperature. Leatherback sea turtles can keep their body temperatures up by constant activity and special adaptations to their circulatory system which enables them to maintain a body temperature of 77 F [25 C] in 42 F [8 C] water.)

Soil and water are heat reservoirs, and so reptiles burrowed underground (buried in the soil or in natural underground hollows or caverns, called hibernaculum) or at the bottom of bodies of water will lose heat more slowly. Because temperatures remain stable at various depths, species that hibernate during the cold winters do so underground or in the mud at the bottom of lakes and rivers, digging down so that they are below the frost line. As the winter turns to spring and the surrounding soil, rock and water begins to slowly warm up over a period of weeks, the hibernating animals warm up and begin to emerge from their hibernation state. While this is normal for species native to these areas, hibernation is not normal for neo-tropical and tropical species moved to these areas, and so these species will die unless they are restored to their proper environment and rewarmed properly.

Hypothermia, then, is the state of the body being so cold as to begin the process of tissue death through the lack of sufficient circulating oxygen to feed the tissue and the beginning of the cessation of systemic functioning.

Hypothermic Reptiles
Cold reptiles are usually dark in color, especially those diurnal species who naturally darken when cold as a way to increase heat absorption when basking. If the hypothermic state set in while the reptile was in a dark place, and being in the dark typically causes a lightening of the skin color, the hypothermic reptile may be light in color. In other words, color alone isn't enough to assess the presence or degree of hypothermia.

The hypothermic reptile will be very cold to the touch and will be unresponsive when touched or handled. The body will be stiff and there will be little to no deep pain reaction (as when the sole of the foot is pressed deeply with your thumbnail).

Treating Hypothermia
The key thing to keep in mind is that, despite your desire to get your reptile warmed back up to basking temperatures as quickly as possible, re-warming must be done slowly. If warmed too fast, tissue destruction may result.

1. Run a lukewarm bath (about 70 F/21 C) and put the reptile in it. If the reptile is small, or a snake or turtle, you may wish to run the water into a plastic container big enough to comfortably hold the reptile, such as a food storage container, wash basin, or use a sink. Since the reptile cannot move freely at this point, be sure to keep the head above water far enough so that the nostrils and mouth are above the water line. Keep refreshing the water to maintain temperature

2. After the reptile has soaked for 20-30 minutes, remove the reptile from the water and dry it off with a warm towel - if the reptile is left wet or damp, the evaporation of the water will cause surface cooling and cool the blood circulating near the surface, which will circulate to the internal organs, cooling them, reversing the process the rewarming

3. When the reptile is dry, wrap it in a warmed towel and place it on a human heating pad in its enclosure or basking area. Do not provide the species normal basking temperatures at this point! Instead, over the course of the next hour or so, gradually increase the environmental temperature until it reaches the high end of the reptiles preferred thermal gradient. After the reptile is warmed and maintained at this temperature for an hour, then increase the environmental temperature until it reaches the species required basking temperatures.

4. Once the reptile has been rewarmed, offer water. You may need to use a syringe or eyedropper to get fluids into it as they may be unwilling to move or too weak yet to drink on their own. When forcing fluids by mouth, go slowly, administering very small amounts at a time, to avoid flooding the mouth and giving the reptile time to close its glottis so fluids don't go down the trachea into the lungs.

5. When caught in time and not exposed to freezing temperatures, most reptiles will recover uneventfully from hypothermia. Within a day or so, they should be eating and drinking normally, as well as returning to their normal daily schedule of waking, basking, and activity. Some may be quieter than usual for several more days, especially if the hypothermia occurred when a reptile escaped from its keeper outdoors.

Why Induced Hypothermia Is Inappropriate for Euthanasia
When reptiles are subjected to freezing temperatures, extracellular fluids begin to form ice crystals long before the reptile loses consciousness and pain perception. This extracellular freezing creates an osmotic imbalance, drawing water out of cells. The circulation is then impeded which inhibits prevents gas exchange, nutrient uptake, etc. Ice crystals begin to create small punctures in cell walls. For more information on euthanasia, see Stephen L. Barten DVM's article, Euthanasia of Reptiles.