Bearded dragons have a third eye called the parietal eye. The parietal eye has a lens, cornea, and retina (Tosini, 1997). The bearded dragons third eye does not see images. Instead, this eye uses a biochemical means to detect light.
Where is a bearded dragons third eye?
The bearded dragons third eye is on the top of its head in between its eyes. It is a pigmented dot on the top of their head and is part of the pineal complex.
The parietal eye is connected to the pineal gland. Together the parietal eye and the pineal gland are known as the pineal complex which are both photosensitive (Tosini, 1997).
How does the third eye work?
The third eye sends signals to the pineal gland by communicating with the optic centre of the brain (Sawnee Animal Clinic).
What does the third eye do?
The role of the pineal complex varies between reptile classes (Tosini, 1997). From as far back as 1958 in experiments by Stebbins and Eakin the parietal eye has been shown to assist diurnal lizards in regulating the amount of sunlight they need and preventing excessive metabolic activity which shortens life. The parietal eye detects light and dark measuring the photoperiod of light (Sawnee Animal Clinic).
The pineal gland (connected to the parietal eye) produces different hormones depending on the time of day including melatonin (Divers and Stahl, 2018) which helps in the sleep and wake cycle. The pineal complex sets the internal clock, detecting the season and even time of day which regulates the production of hormones.
Bearded dragons need to detect light and dark for thermoregulation and production of hormones. The parietal eye plays a role in metabolism. Melatonin is the most important secretory product of the pineal complex and influences thermoregulation (Tosini, 1997).
In some lizards, when the parietal eye was removed, the lizards selected higher temperatures and more exposure to sunlight (Firth et al, 1988) This resulted in higher metabolic activity than that of lizards that still had their parietal eye. The higher metabolic activity shortens life (Stebbins and Eakin,1958).
Research by Tosini and Menaker (1998) on iguana’s found that when the parietal eye was removed there was a slight effect on thermoregulation. However, when the pineal gland was removed, the iguanas could not thermoregulate at all.
In addition, the third eye has a role to play in appetite; level of energy and early warning of predators overhead. The third eye could be the reason why a bearded dragon can become scared, terrified even, about being outside when it is used to being indoors. The change in the quality and brightness in light from artificial light to sunlight may cause the scared reaction of a bearded dragon.
In the Italian wall lizards, it was found through the third eye was required for navigation (Foa et al, 2009). Without it, the lizards could not navigate through a maze.
Stebbins and Eakin (1958) conducted experiments on the parietal eye and although this study is aged, it still holds valuable information. The third eye was removed (parietalectomy) from some iguanid lizards. The results included:
- The lizards were slower to seek refuge from a predator.
- Emerged earlier in the morning.
- Increased time spent in sunlight or artificial light.
- Increased exposure to high temperatures and subsequently greater activity but the body temperature was equivalent to normal lizards. The increased metabolism combined with a lack of food, resulted in dying quicker.
- The thyroid gland was enlarged and had a loss of colloid.
How the bearded dragons third eye impacts husbandry practices
The bearded dragons third eye is an important consideration in husbandry practices. Here are 5 considerations in husbandry practices:
1. Never approaching a bearded dragon from overhead
The third eye is the reason that a bearded dragon should not be approached from overhead. It is also why a bearded dragon can become scared outside with anything flying overhead such as a bird or plane. It is programmed to detect threats coming in from above.
2. Do not provide bearded dragons with light at night
The photosensitive nature of the eye is why bearded dragons need dark at night. The pineal eye can detect light including ultrared and ultraviolet light. This is why lights, whether white or red, should not be used at night, they disturb sleep. Conversely it is also why bright white light should be used during the day. The light directly impacts the biological clock. More on bearded dragons surprising sleep habits here.
3. Moving between sunlight and artificial light
Some bearded dragons can become quite agitated when moving between sunlight and artificial light. It is very likely that the bright sunlight has triggered something through the third eye. The only action is to remain aware of likely changes in behaviour that could occur.
4. Bright tank light is critical to biological functions
As the bearded dragons third eye is photosensitive and is critical to biological functions, it is important to provide bright day light. Ideally sunlight during the day is best however where that is not possible, bright cage lights are needed.
5. Automate the lighting cycles with timers
Along with bright light, lighting cycles are needed to ensure that hormone production and other biological functions of the bearded dragons third eye are working correctly. Automating the lighting cycles will ensure consistency similar to that of the natural environment. For setting up lighting and cycles in the post simplifying lighting.
Bearded Dragons Third Eye Conclusion
The bearded dragons third eye is critical for their biological clock impacting thermoregulation and the production of hormones and as such, is an important consideration in husbandry practices.
It is essential for the bearded dragon’s circadian rhythm that they are provided with total darkness and night and bright white light in the day, preferably sunlight. The third eye is capable of sensing ultrared and ultraviolet light which may disrupt sleep.
Some bearded dragons become scared when going outside or may act differently. This change in behavior may be related to the third eye and the bright natural sunlight which it may not be accustomed to coming through this photosensitive organ. Sunlight, without glass or other barriers, is the best prevention for many illnesses and issues.
- Firth, B., Mauldin, R., & Ralph, C. (1988) The Role of the Pineal Complex in Behavioral Thermoregulation in the Collared Lizard Crotaphytus collaris under Seminatural Conditions. Physiological Zoology, 61(2), 176-185
- Foà, A., Basaglia, F., Beltrami, G., Carnacina, M., Moretto, M., and Bertolucci, C. (2009) Orientation of lizards in a Morris water-maze: roles of the sun compass and the parietal eye. Journal of Experimental Biology. 212: 2918-2924
- Stebbins, R. C., and Eakin, R. M. (1958) The role of the “third eye” in reptilian behavior. American Museum Novitates 1870:1-40
- Tosini, G. (1997) The pineal complex of reptiles: Physiological and behavioral roles. Ethology Ecology & Evolution – Ethology Ecology and Evolution. 9(4)
- Tosini, G., & Menaker, M. (1998) Multioscillatory circadian organization in a vertebrate, iguana iguana. Journal of Neuroscience, 18(3): 1105-1114
- Sawnee Animal Clinic. Cumming. Georgia, USA