by Nicolette L. Cagle, June 1, 2026
In the last post, we opened the box by looking at the Eastern Box Turtle’s participation in the forest-floor food web. We considered the turtle not as an ecosystem service, but as a participant in the exchanges that make the forest floor come alive. Now we look more closely at the turtle itself.
Following Robin Wall Kimmerer’s gift and reciprocity framing, introduced earlier in this series, I want to consider another gift of the Eastern, or Woodland, Box Turtle (Terrapene carolina carolina): the gift of individuality. Individuality is sentimental and value-laden, and it is an ecological and evolutionary reality. A species is not made of identical units; it is made of individual beings that vary.
In evolutionary terms, variation is the raw material upon which natural selection acts. In ecological terms, variation among individuals influences how animals use habitat, respond to stress, encounter predators, reproduce, disperse, or survive changing conditions. Broader ecological research has shown that variation within a species shapes ecological interactions, population dynamics, and community processes (Bolnick et al., 2011). Other work suggests that genotypic (variation in the genes individuals carry) and heritable phenotypic diversity (inherited variation in observable traits, such as size, color, physiology, or behavior) can improve population establishment and persistence (Forsman, 2014).
Variation is also worth celebrating in and of itself. Not every character has a clear current function. Not every color, pattern, behavior, or shape requires or yields an adaptive explanation. Gould and Lewontin (1979) famously cautioned against assuming that every trait must be an optimized adaptation. More recent work on animal coloration makes a similar point, suggesting that while color patterns may reflect camouflage, communication, mate choice, thermoregulation, development, trade-offs, relaxed selection, or neutral variation, sometimes the function remains unclear (Caro, 2021).
Eastern Box Turtles are good teachers when it comes to individuality and variation. The first variation many people notice is the shell. Eastern Box Turtles often have dark carapaces marked with yellow, orange, or reddish streaks, blotches, spots, or radiating lines. These patterns can be striking, but they are not identical. Some turtles are heavily marked, others are darker or more subdued. Some look speckled, others banded or patchy. Maki and colleagues (2025) recently developed digital methods to quantify complex shell color patterns in Eastern Box Turtles, measuring 19 different color-pattern traits from photographs of 55 individuals. Their work is useful because it identifies patterns as measurable variation.
While it is tempting to assume that each mark has a purpose, e.g., camouflage, signaling, thermoregulation, or some other function, that may not be the case. Shell variation might be shaped by genes, development, age, sex, environment, history, or selection, and its function may differ across contexts, or it may not have a clear function at all.
Eye color offers a similar lesson. In adult Eastern Box Turtles, sex is often assessed using multiple secondary sexual characteristics, including tail size and cloacal position, eye coloration, hind claw curvature, and plastron concavity (Edmonds et al., 2020). Field guides and natural-history descriptions often note that males usually have red or orange eyes, while females more often have brown eyes. But “usually” is the operative term. Eye color is helpful, not absolute. A red eye may suggest male, but it is not the whole turtle and experts recommend using at least three different traits or markers to determine the sex of a box turtle.
Using eye color to determine sex became even more interesting when Carlson and colleagues (2020) documented rapid iris color change in Eastern Box Turtles. In males, the iris could shift from pale yellow to bright red in less than five seconds. The authors described this as the first report of rapid eye color change in a non-avian tetrapod and suggested that the change may have a communication function, while also emphasizing the need for further study. This is a fantastic reminder that even a familiar field character is not always fixed.
The shell itself is also more than shape and color. It is a defensive structure, but defense is not purely mechanical. The box turtle’s ability to close depends on anatomy, strength, behavior, and context. Preston and colleagues (2020) tested Eastern Box Turtle responses to simulated predator-induced stress and found that shell closure increased with stimulus intensity. Also, larger and older turtles closed with greater force than smaller and younger turtles. This suggests that the box is not simply open or shut. Closure is graded and varied, and it likely carries costs and constraints.
Warren (2022) also found individual variation in boldness and shell-related behavior. Some turtles emerged from their closed or partially closed position more quickly after disturbance, while others remained closed longer. Some were consistently bolder or shyer. Turtles unable or reluctant to withdraw tightly had lower closing force. These differences are particularly interesting because shell closure is a defining features of box turtles, but it is not experienced identically by every individual.
Boldness has now become one of the clearest ways researchers study box turtle individuality. In behavioral ecology, personality generally refers to consistent individual differences in behavior across time or contexts. This does not refer to personality in the sense that we use it colloquially or for human research, but that doesn’t mean we have to deny animal individuality. As Christine Webb reminds us in The Arrogant Ape, moving beyond human exceptionalism means recognizing that humans are not the only animals with distinctive ways of perceiving and responding to the world. In turtles, “personality” means that individuals can differ predictably in traits such as boldness, exploration, activity, or response to risk, and those differences can have ecological and evolutionary consequences (Réale et al., 2007).
Carlson and colleagues (2024) studied boldness across ten Eastern Box Turtle populations. They found that average boldness did not differ significantly across populations, but the amount of variation among individuals within populations did differ. Temperature, sex, and possibly nearby developed land influenced individual boldness. That result suggests that we miss something if we compare only population averages. Two populations can look similar in average behavior while differing in how much behavioral variation they contain.
In fact, that variation could matter under changing conditions. A bolder turtle may encounter food, mates, roads, predators, or people differently from a shyer turtle. A shy turtle may be safer in one context and more constrained in another. Boldness is not simply good or bad. Its value depends on landscape, season, disturbance, and risk.
Variation also extends inward, beyond what we can see. Harlow and colleagues (2025) examined relationships between box turtle personality and gut microbiomes. They found differences in microbial diversity and community composition associated with sex and boldness categories. This work does not offer a clear causal story since behavior may influence diet and exposure to microbes, while microbiomes may influence physiology and behavior, and behavior and microbiomes might be shaped by habitat, season, sex, or individual history. Still, the study shows that individuality is not only on the outside. It may extend through the body, into digestion, metabolism, and how a turtle approaches its environment.
This is where the gift of individuality becomes especially important for conservation. When we protect a population, we are not only protecting a group of animals. We are protecting variation, including different shell patterns, different behavioral tendencies, different physiologies, different genotypes, different life histories, and different ways of responding to the world.
For long-lived turtles, this is critical. A population with many adults but little recruitment may appear stable while losing hold of its future. A population fragmented by roads may retain some genetic memory of past connectivity while losing present-day mobility. A population reduced by collection, mowing, vehicles, disease, or habitat loss may lose both individuals and the variation that might be needed under future conditions.
Again, it’s important to recall that not every difference has utilitarian value. Variation is not a promise that adaptation will occur, but it does widen the possibility. Without variation, there is less material for selection to work with, less flexibility in response, and fewer ways for a population to meet uncertainty.
The Eastern Box Turtle’s gift of individuality also changes how we observe. A species account can tell us that males often have red eyes, that box turtles have hinged plastrons, that they are omnivorous, that they use forest-floor microhabitats. All of that is true and useful. But the animal in front of us is not the species account. It is one individual turtle, patterned and shaped, sexed and aged, stressed or calm, bold or shy, carrying its own microbial community and its own encounter history of the landscape.
To receive this gift well, we humans have to protect both the species and the variation within it. We must protect connected habitat mosaics so turtles can continue moving, breeding, nesting, dispersing, and encountering different conditions. We need to leave wild turtles in their home landscapes, because removing an individual also removes a particular set of traits and possibilities. We have to support long-term monitoring that can see more than presence or absence. And we can notice difference without forcing every difference into a story.
Individuality asks us to move from categorizing to offering our attention. It asks us to see the Eastern Box Turtle not only as a species with ecological value, but as a population of individuals with meaningful and varied lives. This recalls Thomas Berry’s rejoinder that the universe is “a communion of subjects, not a collection of objects” (Berry, 1999). In that spirit, the individual turtle reminds us that box turtles are not an objects of study, but subjects of their own life stories.
This ends our box turtle series. Please be on the lookout for the next series on the cuckoo family, a cosmopolitan group of birds ranging from road runners to the familiar cuckoos represented by European clocks.
References
Berry T. 1999. The Great Work: Our Way into the Future. New York (NY): Bell Tower.
Bolnick DI, Amarasekare P, Araújo MS, Bürger R, Levine JM, Novak M, Rudolf VHW, Schreiber SJ, Urban MC, Vasseur DA. 2011. Why intraspecific trait variation matters in community ecology. Trends in Ecology & Evolution. 26(4):183–192. https://doi.org/10.1016/j.tree.2011.01.009
Carlson BE, Klein K, Rhodes C. 2020. First report of rapid eye color change in a non-avian tetrapod. Ethology. 126:671–675.
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Gould SJ, Lewontin RC. 1979. The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme. Proceedings of the Royal Society of London. Series B, Biological Sciences. 205(1161):581–598. https://doi.org/10.1098/rspb.1979.0086
Harlow K, Service EK, Geiger JE, Carlson BE, Kimble SJA. 2025. The relationships between box turtle gut microbiomes and personality. PLOS ONE. 20(12):e0339132. https://doi.org/10.1371/journal.pone.0339132
Kimmerer RW. 2024. The Serviceberry: Abundance and Reciprocity in the Natural World. New York (NY): Scribner.
Maki E, Glimm T, Pramanik P, Chiari Y, Kiskowski M. 2025. New approaches for capturing and estimating variation in complex animal color patterns from digital photographs: application to the Eastern Box Turtle (Terrapene carolina). PeerJ. 13:e19690.
Preston SJ, Stengle AG, Sadeghi R, Harms HK, French SS. 2020. Behavioural and physiological responses to simulated predator-induced stress in the Eastern Box Turtle. Conservation Physiology. 8(1):coaa079. https://doi.org/10.1093/conphys/coaa079
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Warren CR. 2022. Bold or boxed?: Testing for morphological and physiological differences between Eastern Box Turtles (Terrapene carolina) with individual variation in boldness [master’s thesis]. Murfreesboro (TN): Middle Tennessee State University.
Webb, C. E. (2025). The arrogant ape: The myth of human exceptionalism and why it matters. Avery.
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