Hermann’s tortoises (Testudo hermanni) are a popular species in the pet trade due to their manageable size compared to many other tortoises. These reptiles, native to Southern Europe, are generally considered small to medium-sized, rarely exceeding 11 inches in length. Their final size is influenced by both genetics and the conditions under which they are raised.
Maximum Adult Size
The average adult Hermann’s tortoise measures between 6 and 11 inches in straight carapace length. Weight generally ranges from 3 to 7 pounds (approximately 1.4 to 3.2 kilograms). Size is measured along the carapace, the upper shell, from the front edge to the back edge.
Mature females usually grow larger and heavier than males of the same subspecies, a disparity known as sexual dimorphism. Tortoises grow very slowly and typically do not reach their full adult size until they are around 10 years old, which is when they reach sexual maturity.
Subspecies Differences in Size
The wide range in adult size is primarily due to two recognized subspecies. The Western Hermann’s tortoise (Testudo hermanni hermanni) is the smaller type, found in regions such as France, Italy, and Spain. Western tortoises rarely exceed 6 or 7 inches in carapace length, with males often maxing out around 5 inches and females reaching up to 6 inches.
The Eastern Hermann’s tortoise (Testudo hermanni boettgeri) is the larger and more commonly kept subspecies in captivity, inhabiting the Balkan regions. Eastern females are the largest of the species, frequently growing to lengths between 8 and 11 inches. Males of the Eastern subspecies commonly reach between 5.5 and 7.5 inches in length.
Factors Influencing Growth
A tortoise’s environment and care play a significant part in whether it achieves its maximum genetic potential in a healthy manner. Healthy growth is characterized by a slow, steady rate, which produces a smooth shell surface. Conversely, rapid growth, often caused by overfeeding or a diet too high in protein, can lead to abnormal development.
The shell condition known as pyramiding, where the scutes on the carapace grow vertically into a stacked, pointed shape, is a sign of unhealthy, accelerated growth in captivity. While excessive protein has historically been cited as a cause, recent research suggests that low environmental humidity is a major contributing factor to pyramiding. Providing high humidity, especially for hatchlings and juveniles, helps prevent the condition by keeping the keratin layer of the shell pliable during growth phases.
Proper care also includes providing the correct basking temperatures and access to UVB light. This is necessary for the tortoise to synthesize Vitamin D3 and properly absorb calcium for healthy bone and shell development.