While many hatchling turtles are rather small, most species attain lengths in excess of 4 inches once mature. Contrary to the claims of ignorant or unscrupulous dealers who assert that turtles will remain small if kept in tiny enclosures, healthy turtles grow quickly when provided with proper care. Nevertheless, a few turtle species remain relatively small and are relatively easy to accommodate.
Mud and Musk Turtles
Mud (Kinosternon spp.) and musk (Sternotherus spp.) turtles are two common, hardy species that remain rather small. While most remain less than 5 inches in length, a few individuals may grow slightly larger. Mud and musk turtles are primarily aquatic, though they require a small land area on which they can bask. Mud and musk turtles are omnivorous, but they primarily consume insects, fish, worms and carrion in the wild.
Box turtles (Terrapene spp.) are relatively small turtles who typically reach lengths between 4 and 6 inches. Box turtles are terrestrial turtles, although they appreciate a large, shallow water reservoir in their enclosure. Box turtles are omnivores, who require a diet including insects, fruits and vegetables.
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Spotted turtles (Clemmys guttata) are an attractive, semi-aquatic species, who generally grow to about 4 or 5 inches in length. They require an enclosure with nearly equal amounts of land area and water, but keep the water shallow, as spotted turtles drown easily. Spotted turtles are largely carnivorous, so they thrive on a diet of worms, insects and feeder fish. Close relatives of spotted turtles, bog turtles (Clemmys muhlenbergii), usually remain less than 5 inches in length, although they are protected in much of their native range, and therefore illegal to keep as a pet.
A close relative of the spotted turtle -- the bog turtle (Clemmys muhlenbergii) -- also remains small. Rarely exceeding 4 inches in length, the bog turtles are the perfect size for captivity, but as their wild populations are declining, some states afford them legal protection and prohibit their possession. Like spotted turtles, bog turtles are semi-aquatic omnivores.
South African tortoises of the genus Homopus represent the smallest turtles in the world. Although they often remain less than 4 inches in length, these tiny turtles are very difficult to keep in captivity and are not suitable for most people seeking a pet. Additionally, because their populations are declining in the wild, they receive legal protection and are rarely available in the pet trade.
Sex and Size
Many turtle species are sexually dimorphic, as animals of one sex grow larger than animals of the opposite sex. In large species, such as African spurred tortoises (Geochelone sulcata), males often grow to larger sizes than females do. However, many small lineages exhibit the opposite trend, with females outgrowing males. This means that hobbyists seeking small turtles should opt for males, rather than females. Unfortunately, it is often difficult to determine the gender of a turtle until they have matured. Although the characteristics which distinguish males from females differ from one species to the next, males generally have longer tails than females do, and their plastrons are concave. The curved shape of the lower shell allows males to mount females.
In the United States, federal law prohibits the sale of turtles with carapace lengths of less than 4 inches. The only exceptions to this law, according to the U.S. Department of Agriculture, are for turtles sold for scientific, educational or exhibitional purposes. Accordingly, the many quarter-sized turtles in pet stores and reptile expos are not legal to sell to people seeking pet turtles.